US20040160227A1 - Apparatus and method for determining the status of an electric power cable - Google Patents

An apparatus (100) and method (300) for determining the status of a electric cable (20) is provided. The apparatus (100) rigidly includes a probe (104) having coaxial contacts (150, 152) and including a melt unit (102) configured to melt an insulating jacket (32) of the cable (20), an instrumentation unit (106) coupled to the probe (104) and housing a cable analysis circuit (186), a status display unit (188) coupled to the instrumentation unit (106), an insulated shank (108) coupled to the instrumentation unit (106), and a hotstick adapter (110) coupled to the insulated shank (108). The cable analysis circuit (186) includes a connection determination circuit (200) configured to determine if an electrical connection between the probe (104) and the cable (20) is a valid connection, and a status determination circuit (222) configured to determine the status of the cable (20) while the electrical connection is a valid connection. The status display unit (188) includes a plurality of visual indicators (236) configured to impart connection condition and cable status to the user.

RELATED INVENTION

• The present invention claims benefit under 35 U.S.C. §119(e) to “Apparatus and Method for Determining if an Underground Cable Is Energized and for Identifying Its Phase,” U.S. Provisional Patent Application Serial No. 60/448,161 filed 18 Feb. 2003, which is incorporated by reference herein.

• The present invention also claims benefit under 35 U.S.C. §119(e) to “Apparatus and Method for Probing Jacketed Underground Distribution Cable,” U.S. Provisional Patent Application Serial No. 60/519,319 filed 12 Nov. 2003, which is incorporated by reference herein.

TECHNICAL FIELD OF THE INVENTION

• The present invention relates to the field of electric power distribution networks. More specifically, the present invention relates to determining the status of underground residential distribution power cables.

BACKGROUND OF THE INVENTION

• Electric power distribution networks are used by the electric utilities to deliver electricity from generating plants to customers. Although the actual distribution voltages will vary from utility to utility, in a typical network, three-phase power at high voltage (345,000 volts phase-to-phase) is delivered to multiple transmission substations at which transformers step this high voltage down to a lower three-phase voltage (69,000 volts phase-to-phase). This 69,000-volt three-phase power then feeds multiple distribution substations whose transformers further step down the voltage to the distribution voltage (12,470 volts phase-to-phase) and separate the power into three single-phase feeder cables. Typically, these feeder cables operate at 7,200 volts phase-to-ground. Each of these feeder cables branch into multiple circuits to power a plurality of local pole-mounted or pad-mounted transformers which step the voltage down to a final voltage of 120/240 volts for delivery to commercial and residential customers.

• In many cases, the final 7,200-volt distribution network utilizes underground (i.e., buried) cables. These cables are typically known as underground residential distribution (URD) cables. Typical URD cables are shown in FIGS. 1 and 2.

• In a

  typical URD cable

  20, a

  central conductor

  22 is surrounded by an

  inner semiconductor sheath

  24.

  Inner semiconductor sheath

  24 serves to relieve electrical stress by spreading out and making the electrical field more uniform.

• Inner semiconductor sheath

  24 is surrounded by an

  insulator

  26.

  Insulator

  26 has significant high-voltage insulating properties to minimize the overall size of

  URD cable

  20. Typically,

  insulator

  26 is formed of a polymeric material, such as polyethylene.

• Surrounding

  insulator

  26 is an

  outer semiconductor sheath

  28. Like

  inner sheath

  24,

  outer sheath

  28 serves to relieve electrical stress by making the electrical field more uniform. Making the electrical field more uniform protects

  insulator

  26, which would otherwise be more likely to break down.

• Outer semiconductor sheath

  28 is surrounded by a shield formed of a plurality of

  neutral conductors

  30.

  Neutral conductors

  30 together serve as a return line for

  central conductor

  22. In a typical three-phase system,

  neutral conductors

  30 carry current resulting from any imbalance among the three phases. In a mechanical sense,

  neutral conductors

  30 form a barrier to protect

  URD cable

  20 from casual penetration (as with a blunt shovel). In the event of a catastrophic penetration through

  neutral conductors

  30 and into or through

  central conductor

  22,

  neutral conductors

  30 serve to provide a short electrical path and thereby offer some protection to a worker wielding the penetrating object.

• Semiconductor layers

  24 and 28 prevent high stress electrical field lines from forming under each

  neutral conductor

  30. But as a side effect,

  semiconductor layers

  24 and 28 also impede detection of the electrical field from outside of

  layer

  28.

• URD cable

  20 may be an

  unjacketed URD cable

  20′ (FIG. 1). In

  unjacketed URD cable

  20′,

  neutral conductors

  30 form the outermost layer of the cable.

  Neutral conductors

  30 are therefore in contact with the Earth when

  unjacketed URD cable

  20′ is buried.

• URD cable

  20 may also be a jacketed

  URD cable

  20″. In jacketed

  URD cable

  20″,

  neutral conductors

  30 are surrounded by and embedded within an

  insulating jacket

  32. Whether

  URD cable

  20 is jacketed or unjacketed,

  neutral conductors

  30 need not be grounded, but usually are grounded at the ends.

• As new customers are added,

  URD cable

  20 is cut and an extension cable is spliced in to supply power to the new customer's transformer. This poses certain problems.

• One problem is that there are often

  multiple URD cables

  20 in a given trench, conduit, or raceway. Typically, one of these

  URD cables

  20 is de-activated prior to splicing. A problem exists in determining which of these

  multiple URD cables

  20 is de-energized (i.e., “dead”).

• Clamp-on ammeters are occasionally used in an attempt to determine if a

  URD cable

  20 is dead. Since each

  URD cable

  20 carries its own return, the ammeter is used to measure differential current. But a reading of zero current may result from two very different conditions. Either the cable is in-fact a dead cable, or the cable is live but nearly perfectly balanced. Since one of the goals of electrical distribution is to achieve perfect balance, the value of the test becomes more meaningless as this goal is more closely achieved. Consequently, many live cables are misdiagnosed as being dead.

• Another related problem is that, in a given dig, extraneous

  unmapped URD cables

  20 may be present. These

  extraneous URD cables

  20 may or may not be energized, and will often confuse ammeter measurements to the point where it is impossible to determine which of the

  URD cables

  20 is the de-energized

  URD cable

  20 to be cut and spliced.

• When a

  URD cable

  20 is to be cut and spliced, it is first spiked. That is, a “spike”is driven through the selected

  URD cable

  20 to short

  neutral conductors

  30 to

  center conductor

  22. If the

  spiked URD cable

  20 is live, then spiking will create a short circuit and trip the appropriate circuit breakers. This assures that the worker will not cut into a

  live URD cable

  20.

• The spiking of a

  live URD cable

  20 is undesirable for several reasons. First, spiking a

  live URD cable

  20 poses a risk to the worker, albeit a risk significantly less than the cutting of a

  live URD cable

  20. Second, tripping the circuit breaker causes an unnecessary power outage to all customers served by that

  URD cable

  20. Third, unnecessarily spiking a

  URD cable

  20 necessitates a repair of that

  URD cable

  20. Spiking a

  live URD cable

  20, therefore, is dangerous, costly, and time consuming.

• Various apparatus have been developed to identify the status, live or dead, of

  URD cables

  20. All of these apparatuses suffer from one or more deficiencies. When attempting to use such apparatuses to identify the status of a given

  URD cable

  20, there are four primary conditions:

• True-dead—identifying a given

  URD cable

  20 as dead when it is in fact dead;

• False-dead—identifying a given

  URD cable

  20 as dead when it is in fact live;

• True-live—identifying a given

  URD cable

  20 as live when it is in fact live; and

• False-live—identifying a given

  URD cable

  20 as live when it is in fact dead.

• A false-live result may cause the worker to backtrack and double-check the removal of power from the desired

  URD cable

  20, may cause additional and unnecessary excavation, and may cause further labor and paperwork. This may result in a waste of time and resources. But a false-dead result, on the other hand, may lead to misidentification of the

  specific URD cable

  20 to be cut and spliced. This is the worst possible scenario, in that the worker would then spike a

  live URD cable

  20, believing it to be dead. As previously mentioned, spiking a

  live URD cable

  20 is dangerous, costly, and time-consuming.

• The only good status results are then a true-live and a true-false. Only such results will properly identify the

  specific URD cable

  20 to be spiked, cut, and spliced, thereby safely, inexpensively, and efficiently allowing the work to proceed.

• Apparatuses intended to determine status almost invariably test to determine if a

  URD cable

  20 is live. No active test is performed to determine if

  URD cable

  20 is dead. The presumption is, of course, that if

  URD cable

  20 is not live, it is dead. This is a dangerous presumption.

• If such an apparatus determines a

  URD cable

  20 is live, it is often correct. That is, such an apparatus produces a reasonably reliable true-live result, with few false-live results. On the other hand, such an apparatus does not positively determine if

  URD cable

  20 is dead. The apparatus can therefore only determine if

  URD cable

  20 is “not-live”.

  URD cable

  20 may test not-live if it is dead, or if it is live and the test fails for whatever reason, including worker error. This form of test therefore exhibits a high incidence of false-dead results. This is the worst possible scenario, in that the worker would then spike a

  live URD cable

  20, believing it to be dead.

• Another problem with many apparatuses for determining the status of

  URD cables

  20 is that they are cumbersome to use. Often, an apparatus (or a portion of the apparatus) must be clamped to the

  URD cable

  20 under test. This requires the worker to get down into a trench or otherwise obtain direct access to and manipulate

  URD cable

  20.

• Many such apparatuses are usable only with

  unjacketed URD cables

  20′.

  Unjacketed URD cables

  20 suffer from corrosion and other factors that shorten their useful lifetimes. For this reason, the cable of choice for newer installations is almost invariably jacketed

  URD cable

  20″. In order to use an apparatus designed for

  unjacketed URD cable

  20′ with a

  jacketed URD cable

  20″, a portion of the insulating

  jacket

  32 must be cut away, drilled, or otherwise penetrated. This, too, requires that the worker obtains direct access to and manipulates

  URD cable

  20.

• Because the

  URD cables

  20 may carry high voltage (typically 7,200 volts), any procedure requiring direct manipulation of the cable is inherently dangerous. A faulty or misidentified cable may expose the worker to high voltage, and potentially precipitate injury or death. Additionally, all procedures requiring direct manipulation of the cable are cumbersome, costly, and time-consuming. This is especially true for a

  jacketed URD cable

  20″ being tested with an apparatus intended for an

  unjacketed URD cable

  20″. When a portion of the insulating

  jacket

  32 has been cut away and that

  URD cable

  20 is determined to not be the

  URD cable

  20 to be cut and spliced, then that

  URD cable

  20 must then be repaired to protect it from corrosion and other factors that would otherwise shorten its useful lifetime. This repair is itself cumbersome, costly, and time-consuming.

• Cumbersome and time-consuming procedures often inspire workers to shortcut the testing procedure. This may lead to injury or death, as well as expensive and time-consuming error.

• Even those apparatuses which do not require the worker to enter the trench often require the worker to insert the apparatus into the trench to make a measurement, then remove the apparatus from the trench to obtain the results. Such apparatuses are often difficult to maneuver from a distance. For example, one such apparatus has two probes more than 3 cm apart, and is configured to be attached to a hotstick. In order to establish a proper connection, the apparatus must be positioned so that the two probes are oriented longitudinally with the

  URD cable

  20 and the hotstick and apparatus are perpendicular to the URD cable. This requires careful manipulation on the part of the worker. Such careful manipulation is awkward and cumbersome to perform in the field, and inspires the worker to shortcut the testing procedure by making a minimum number of tests (often a single test, especially where a desired result is obtained) where a plurality of tests is required for positive results.

• Many apparatuses for determining the status of a

  URD cable

  20 do so by detecting the presence of an electric field in or around a

  live URD cable

  20. This field is very weak, on the order of a few millivolts at best. Since the URD cables carry high voltages at respectable currents, the environment in which the tests are performed is generally electrically noisy. The combination of low signal strength and a noisy environment creates a tendency for such apparatuses to indicate false-live statuses. This is especially true of those apparatuses having lengthy and or unshielded input lines. Of course, an apparatus may be designed to obtain fewer false-live readings at the expense of more false-dead readings. But this would only lead to a less usable apparatus. Since the false-dead condition is even worse than the false-live condition.

• Many apparatuses have a first portion contacting the

  URD cable

  20 under test and a second portion indicating the test results, where the first portion is naturally in the trench or raceway with the

  URD cable

  20 and the second portion is with the operator. Alternatively, many apparatuses derive power from a generator or work vehicle. In both cases, there is a cable or line extending from the URD cable to a person or object outside of the trench or raceway. This poses a significant hazard in that a

  defective URD cable

  20, or a penetration of an otherwise

  good URD cable

  20, may cause the high voltage to be conducted over the line to a point outside the trench or raceway. Once high voltage is out of the trench or raceway, there is a danger that an individual may come into contact with the high voltage and suffer injury or death as a result. In addition, this high voltage may find a path through equipment which may subsequently become damaged or destroyed.

SUMMARY OF THE INVENTION

• Accordingly, it is an advantage of the present invention that an apparatus is provided for determining the status of an underground residential distribution (URD) cable.

• It is another advantage of the present invention that an apparatus is provided that actively tests a URD cable for both a live and a dead status.

• It is another advantage of the present invention that an apparatus is provided that determines the status of a URD cable while the worker is safely at a distance from the URD cable.

• It is another advantage of the present invention that an apparatus is provided that displays results viewable at a distance.

• It is another advantage of the present invention that an apparatus is provided that determines a quality of connection to a URD cable while determining the status thereof.

• It is another advantage of the present invention that an apparatus is provided that determines the status of a URD cable in an easy and straightforward manner.

• The above and other advantages of the present invention are carried out in one form by an apparatus for determining the status of a URD cable in an electric power network operating at a line frequency. The apparatus includes a rigid probe with a common contact configured to contact a neutral conductor of the URD cable, and an input contact insulated from the common contact and configured to contact an outer semiconductor sheath of the URD cable. The apparatus also includes an instrumentation unit rigidly coupled to the probe, a cable analysis circuit housed within the instrumentation unit and electrically coupled to the common and input contacts, and a status display unit electrically coupled to the cable analysis circuit.

• The above and other advantages of the present invention are carried out in another form by an apparatus for determining the status of a URD cable in an electric power network. The apparatus includes a probe configured to establish an electrical connection with the URD cable, wherein the electrical connection consists of a common contact of the probe in contact with a neutral conductor of the URD cable, and an input contact of the probe in contact with an outer semiconductor sheath of the URD cable. The apparatus also includes a cable analysis circuit coupled to the probe. This circuit simultaneously determines if the electrical connection is a valid connection while determining the status of the URD cable. A status display unit is coupled to the cable analysis circuit and configured to indicate the status of the URD cable when the electrical connection is a valid connection.

BRIEF DESCRIPTION OF THE DRAWINGS

• A more complete understanding of the present invention may be derived by referring to the detailed description and claims when considered in connection with the Figures, wherein like reference numbers refer to similar items throughout the Figures, and:

• FIG. 1 shows a cross-sectional view of a typical prior-art unjacketed underground residential distribution (URD) cable;

• FIG. 2 shows a cross-sectional view of a typical prior-art jacketed URD cable;

• FIG. 3 shows a side view of a power-cable status determination apparatus in accordance with a preferred embodiment of the present invention;

• FIG. 4 shows a cross-sectional side view of a portion of the apparatus of FIG. 3 for use with an unjacketed URD cable in accordance with a preferred embodiment of the present invention;

• FIG. 5 shows an end view of the apparatus portion of FIG. 4 in accordance with a preferred embodiment of the present invention;

• FIG. 6 shows a cross-sectional side view of a melt unit for the apparatus of FIGS. 3 and 4 for use with a jacketed URD cable in accordance with a preferred embodiment of the present invention;

• FIG. 7 shows an end view of the melt unit of FIG. 6 in accordance with a preferred embodiment of the present invention;

• FIG. 8 shows a schematic view of the electrical characteristics of a URD cable in accordance with a preferred embodiment of the present invention;

• FIG. 9 shows a schematic view of an equivalent circuit of a URD cable in accordance with a preferred embodiment of the present invention;

• FIG. 10 shows a flow chart of a method for determining the status of a URD cable using the apparatus of FIG. 3 in accordance with a preferred embodiment of the present invention;

• FIG. 11 shows a cross-sectional side view of the apparatus of FIGS. 3 and 4 in contact with an unjacketed URD cable in accordance with a preferred embodiment of the present invention;

• FIG. 12 shows a cross-sectional side view of the apparatus of FIGS. 3, 4, and 5 in contact with a jacketed URD cable in accordance with a preferred embodiment of the present invention;

• FIG. 13 shows a schematic block diagram of a cable analysis circuit for the apparatus of FIG. 3 in accordance with a preferred embodiment of the present invention;

• FIG. 14 shows a plan view of a status display panel for the apparatus of FIG. 3 depicting no electrical connection in accordance with a preferred embodiment of the present invention;

• FIG. 15 shows a plan view of the status display panel of FIG. 14 depicting a “short” or low-resistance electrical connection in accordance with a preferred embodiment of the present invention;

• FIG. 16 shows a plan view of the status display panel of FIG. 14 depicting an “open” or high-resistance electrical connection in accordance with a preferred embodiment of the present invention;

• FIG. 17 shows a plan view of the status display panel of FIG. 14 depicting a “dead” or de-energized URD cable status in accordance with a preferred embodiment of the present invention;

• FIG. 18 shows a plan view of the status display panel of FIG. 14 depicting an “unknown” or indeterminate URD cable status in accordance with a preferred embodiment of the present invention; and

• FIG. 19 shows a plan view of the status display panel of FIG. 14 displaying a “live” or energized URD cable status in accordance with a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

• FIGS. 1 and 2 show cross-sectional views of typical underground residential distribution (URD)

  cables

  20, with FIG. 1 showing an

  unjacketed URD cable

  20′ and FIG. 2 a

  jacketed URD cable

  20″. FIG. 3 shows a side view of an

  apparatus

  100 that determines the status of a

  URD cable

  20 in accordance with a preferred embodiment of the present invention. FIG. 4 shows a cross-sectional side view and FIG. 5 an end view of a portion of

  apparatus

  100 for use with

  unjacketed URD cable

  20′ in accordance with a preferred embodiment of the present invention. FIG. 6 shows a side view and FIG. 7 an end view of a

  melt unit

  102 for

  apparatus

  100 for use with

  jacketed URD cable

  20″ in accordance with a preferred embodiment of the present invention. The following discussion refers to FIGS. 1 through 7.

• Status determination apparatus

  100 is a probing device configured to engage

  URD cable

  20 and determine the status thereof.

  Apparatus

  100 is a rigid structure made up of a

  probe

  104 to which is coupled an

  instrumentation unit

  106, to which is coupled an

  insulated shank

  108, to which is coupled a

  hotstick adapter

  110. By being rigid,

  apparatus

  100 allows the worker to couple

  apparatus

  100 to a hotstick and use the apparatus as an extension of the hotstick to contact

  URD cable

  20 from a distance. This allows the user to determine the status of

  URD cable

  20 without necessitating direct manipulation of

  URD cable

  20 by the worker. This significantly increases ease of use and overall safety.

• Hotstick adapter

  110 is a

  standardized hotstick adapter

  110 used in the industry to couple to a hotstick (not shown), which is an insulated extension pole. The use of a hotstick allows

  apparatus

  100 to be used at a distance from the worker, as in the bottom of a deep trench. This allows the worker to determine the status of a

  URD cable

  20 safely and conveniently from outside the trench.

• Insulated shank

  108 has an

  adapter end

  112 and an

  instrumentation end

  114 opposing

  adapter end

  112.

  Hotstick adapter

  110 is rigidly coupled to adapter end 112 of

  insulated shank

  108. When

  apparatus

  100 is used with a hotstick, the hotstick is coupled to

  hotstick adapter

  110, and

  insulated shank

  108 serves as an extension of the hotstick. When

  apparatus

  100 is used without a hotstick (as when

  URD cable

  20 is at the surface or in a raceway), then insulated

  shank

  108 serves as a short hotstick to provide ease of use while maintaining safety for the worker.

• Instrumentation unit

  106 has a

  probe side

  116 and a

  display side

  118 opposing

  probe side

  116.

  Instrumentation end

  114 of

  insulated adapter

  108 is rigidly coupled to

  display side

  118 of

  instrumentation unit

  106.

• Probe

  104 has an

  active end

  120 and an

  instrumentation end

  122 in opposition to

  active end

  120.

  Instrumentation end

  122 is rigidly coupled to probe

  side

  116 of

  instrumentation unit

  106. Together,

  probe

  104,

  instrumentation unit

  106,

  insulated shank

  108, and

  hotstick adapter

  110 form a rigid structure for

  apparatus

  100.

• The methodologies used to couple

  probe

  104 to

  instrumentation unit

  106,

  instrumentation unit

  106 to

  insulated shank

  108, and

  insulated shank

  108 to

  hotstick adapter

  110 are commonplace in the industry and well known to those of ordinary skill in the art. These methodologies are therefore not discussed herein.

• Probe

  104 is made up of

  melt unit

  102 and a

  probe body

  124. In the preferred embodiment,

  melt unit

  102 is detachably and rigidly coupled to probe

  body

  124 by female and

  male threads

  126 and 128, respectively. This allows

  melt unit

  102 to be removed from

  probe body

  124 when

  probe

  104 is to be used with

  unjacketed URD cable

  20′, and allows

  melt unit

  102 to be coupled to probe

  body

  124 when

  probe

  104 is to be used with

  jacketed URD cable

  20″.

• When

  melt unit

  102 is removed from

  probe body

  124,

  melt unit

  102 is typically still hot. An effective way of removing

  melt unit

  102 without risk of injury is to slip a pocket-like hot pad (not shown) over

  melt unit

  102. The hot pad may then be used to unscrew and remove

  melt unit

  102 from

  probe body

  124.

  Melt unit

  102 may then be stored within the hot pad until cool. A typical pocket-like hot pad for this use is the type universally sold for use over the handle of a cast-iron skillet. Any similar pocket-type hot pad will also work.

• Those skilled in the art will appreciate that it is not a requirement of the present invention that melt

  unit

  102 be detachable from

  probe body

  124. In an alternative embodiment,

  apparatus

  100 may be produced for use with

  unjacketed URD cable

  20′ only. In this embodiment,

  probe

  104 would lack

  melt unit

  102 completely. In another alternative embodiment,

  apparatus

  100 may be produced for use with

  jacketed URD cable

  20″ only. In this embodiment,

  probe

  104 might have

  melt unit

  102 fixedly and rigidly coupled to probe

  body

  124. The differences in the internal construction of probe 104 (discussed hereinafter) to effect these alternative embodiments would be obvious to one of ordinary skill in the art and are not discussed herein.

• When

  apparatus

  100 is used with

  unjacketed URD cable

  20′,

  melt unit

  102 is desirably omitted and probe 104 is made up solely of probe-

  body

  124. Probe

  body

  124 is made up of a cylindrical

  outer shell

  130 and a

  central input conductor

  132. Cylindrical

  outer shell

  130 is electrically conductive, but desirably somewhat resistive to thermal conduction. A typical material for

  outer shell

  130 is stainless steel.

• An

  insulator

  134 separates shell 130 and

  input conductor

  132. Desirably,

  outer shell

  130,

  insulator

  134, and

  input conductor

  132 are all coaxial. By being coaxial,

  probe body

  124 rejects extraneous noise during determination of the status of URD cable 20 (discussed in greater detail hereinafter). By being coaxial,

  probe body

  124 more easily establishes an electrical connection with

  URD cable

  20 than apparatuses having multiple non-coaxial probes (discussed in more detail hereinafter).

• Input conductor

  132 is made up of a

  conductive spring

  138, a

  movable conductor portion

  140, and an

  input contact

  142. In the embodiment depicted in FIG. 4, a fixed

  conductor portion

  136 is fixedly coupled within

  insulator

  134.

  Movable conductor portion

  140 is movably coupled within

  insulator

  134.

  Conductive spring

  138 electrically couples fixed and

  movable conductor portions

  136 and 140.

  Input contact

  142 is coupled to

  movable conductor portion

  140. In another embodiment (not shown),

  movable conductor

  140 is a solid rod that extends entirely through

  probe body

  124. A flexible wire connects

  movable conductor

  140 to an electrical circuit, and

  spring

  138 is located inside

  instrument housing

  106.

  Spring

  138 then pushes against

  conductor portion

  140 but is substantially electrically isolated from the electronic signal conveyed by

  conductor portion

  140. Both embodiments allow

  input contact

  142 to be spring loaded, but this is not a requirement of the present invention.

• In one alternate embodiment,

  input contact

  142 may be detachably coupled to

  movable conductor portion

  140. This allows

  input contact

  142 to be changed if worn or damaged, but is not a requirement of the present invention. Those skilled in the art will appreciate that

  input contact

  142 may also be integral to

  movable conductor portion

  140 without departing from the spirit of the present invention.

• Outer shell

  130 of

  probe body

  124 incorporates a circular

  common contact

  144 and

  male threads

  128.

  Male threads

  128 allow

  probe body

  124 to couple to melt

  unit

  102 as required.

• Probe body

  124 has an

  instrumentation end

  146 and an

  active end

  148. When

  apparatus

  100 is used to determine the status of

  unjacketed URD cable

  20′, then melt

  unit

  102 is desirably omitted. Probe-

  body instrumentation end

  146 then serves as

  probe instrumentation end

  122, and probe-body

  active end

  148 serves as probe

  active end

  120. Probe-body input and

  common contacts

  142 and 144 then serve as probe input and

  common contacts

  150 and 152, respectively, and are located at probe

  active end

  120.

• Probe body

  124 has a

  length

  154 of not more than 32.0 cm, and desirably has a

  length

  154 of approximately 16.5 cm. In use,

  apparatus

  100 is typically attached to a hotstick (not shown) and placed into contact with a

  URD cable

  20 located in the bottom of a trench while the worker remains safely outside the trench. For use with

  unjacketed URD cable

  20′,

  probe

  104 desirably consists of

  probe body

  124, with

  instrumentation unit

  106 coupled to the

  instrumentation end

  122 of

  probe

  104. It is desirable, therefore, that

  probe body

  124 be long enough to allow the worker to see

  active end

  120 of

  probe

  104 around

  instrumentation unit

  106 as

  probe

  104 makes contact with

  URD cable

  20. Conversely, the

  longer probe body

  124 is, the more

  susceptible apparatus

  100 is to electrical noise (discussed hereinafter). A compromise is desirably reached between these two opposing requirements. A

  maximum length

  154 of 32.0 cm, and a

  desirable length

  154 of approximately 16.5 cm, for

  probe body

  124 successfully effects that compromise in the preferred embodiment.

• Additionally,

  probe body

  124 has a

  diameter

  156 of not more than 6.0 cm. This provides a

  distance

  158 between input and

  common contacts

  150 and 152 of not more than 3.0 cm. Desirably, probe body has a

  diameter

  156 of approximately 1.6 cm, providing a

  nominal distance

  158 between

  contacts

  150 and 152 of 0.8 cm. By having a

  single probe

  104 with two

  contacts

  150 and 152 separated by less than 3.0 cm, an electrical connection between

  probe

  104 and

  URD cable

  20 is greatly facilitated over multi-probe apparatuses having a greater distance between contacts.

• By having input contact 150 within and coaxial with

  common contact

  152, a significant increase in the ease of establishing an electrical contact between

  probe

  104 and

  URD cable

  20 is realized.

  Apparatus

  100 need only establish an electrical contact between

  common contact

  152 and any single

  neutral conductor

  30 of

  URD cable

  20, and need only establish an electrical contact between

  input contact

  150 and any point on

  outer semiconductor sheath

  28 of

  URD cable

  20.

  Common contact

  152 is configured as a ring or lip at the active end of

  probe

  104, and

  input contact

  150 is configured as a pin coaxial with

  common contact

  152. This two-point contact scheme allows

  probe

  104 to successfully establish electrical contact with

  URD cable

  20 while

  apparatus

  100 is off-center and non-perpendicular to

  URD cable

  20, i.e., while the worker holds the hotstick with

  apparatus

  100 attached at any of a wide variety of angles and

  contacts URD cable

  20 at any of a wide variety of on- and off-axis locations. This is in marked contrast to two-probe apparatuses that require a specific orientation to

  URD cable

  20 to effect contact.

• In addition, by having

  contacts

  150 and 152 separated by less than 3.0 cm, a significant reduction in electrical noise (discussed hereinafter) may be realized by

  apparatus

  100. This is especially true because, for

  probe body

  124,

  input conductor

  132 is coaxial with and shielded by

  outer shell

  130.

• Those skilled in the art will appreciate that probe-

  body

  124 may be produced with dimensions other than those given herein without departing from the spirit of the present invention.

• When

  apparatus

  100 is to be used with

  jacketed URD cable

  20″, then melt

  unit

  102 is coupled to probe

  body

  124, and probe 104 is made up of probe-

  body

  124 and melt

  unit

  102.

  Melt unit

  102 is made up of a

  thermal reservoir

  160, a

  thermal insulator

  162, and a

  coupling component

  164.

  Coupling component

  164 contains

  female threads

  126 and serves to couple

  melt unit

  102 to probe-

  body

  124.

• Thermal reservoir

  160 is made up of a thermally massive, thermally and electrically conductive cylindrical

  outer shell

  166 and a thermally and electrically conductive

  central input conductor

  168.

  Outer shell

  166 serves as the primary thermal component of

  thermal reservoir

  160. For this reason, outer shell is desirably fabricated of a thermally retentive material, such as aluminum or aluminum alloys.

• A thermally conductive

  electrical insulator

  170 separates shell 166 and

  input conductor

  168. Since

  outer shell

  166 serves as the primary thermal component of

  thermal reservoir

  160,

  insulator

  170 is preferably small in cross section in order to maximize the mass of

  outer shell

  166.

  Outer shell

  166,

  insulator

  170, and

  input conductor

  168 are all mutually coaxial.

• Input conductor

  168 is made up of a fixed

  conductor portion

  172 and an

  input contact

  174. In the preferred embodiment,

  input contact

  174 is detachably coupled to fixed

  conductor portion

  172. This allows

  input contact

  174 to be changed if a

  cable

  20″ with unusually large or small diameter

  neutral conductors

  30 is encountered of if

  input contact

  174 becomes worn or damaged. But this is not a requirement of the present invention. Those skilled in the art will appreciate that

  input contact

  174 may be integral to fixed

  conductor portion

  172 without departing from the spirit of the present invention.

• Melt unit

  102 has an

  active end

  178 and a

  body end

  180.

  Outer shell

  166 of

  melt unit

  102 incorporates a circular

  common contact

  176 configured as a ring or lip at

  active end

  178. The ring or lip projects outward only for a distance that is slightly greater than the distance between the outside surface of

  neutral conductors

  30 and the outside of

  jacket

  32 of

  cable

  20″, e.g., about 3.8 mm.

• When

  melt unit

  102 is used to establish electrical contact with

  jacketed URD cable

  20″,

  body end

  180 is coupled to

  active end

  148 of

  probe body

  124. Probe-

  body instrumentation end

  146 then serves as

  probe instrumentation end

  122, and melt-unit

  active end

  178 then serves as probe

  active end

  120. Melt-unit input and

  common contacts

  174 and 176 then serve as probe input and

  common contacts

  150 and 152, respectively, and are located at probe

  active end

  120.

  Input contact

  174 desirably projects beyond

  common contact

  176 by a distance roughly equal to or slightly greater than the diameter of a

  neutral conductor

  30, e.g., about 2.5 mm.

• When preparing

  melt unit

  102 to melt insulating

  jacket

  32 of

  jacketed URD cable

  20″,

  thermal reservoir

  160 is heated by applying heat from an external heat source 181 (FIG. 10).

  External heat source

  181 is a source of heat external to

  apparatus

  100. This allows

  apparatus

  100 to be self-contained without having to provide sufficient power to heat

  melt unit

  102. Typical

  external heat sources

  181 may be a torch or a heating unit powered by line or vehicular current.

• Thermal reservoir

  160 is desirably heated to a temperature suitable for melting insulating

  jacket

  32 of

  jacketed URD cable

  20″. This temperature is desirably around 200-250° C. To prevent overheating of

  thermal reservoir

  160, a thermometer 183 (FIG. 6) may be used to measure an inside temperature of

  thermal reservoir

  160. To facilitate this, a

  thermometer connector

  182 is provided in

  thermal reservoir

  160.

  Thermometer connector

  182, in its simplest form, need only be a hole into the end of

  thermal reservoir

  160 into which the sensing end of

  thermometer

  183 is inserted during heating.

• Thermal reservoir

  160 desirably has sufficient mass to maintain a temperature suitable to melt insulating jacket 32 a plurality of times. In the preferred embodiment, thermal reservoir has sufficient mass to maintain a melting temperature for at least five normal status determinations.

• Thermal insulator

  162 provides a barrier between

  thermal reservoir

  160 and

  coupling component

  164. This impedes the heat from thermal reservoir from traveling up

  probe

  104. Desirably,

  thermal insulator

  162 is configured of a non-thermally conducting material, such as polytetrafluorethylene (a.k.a. Teflon®) or lava rock.

• Electrical continuity between

  probe body

  124 and

  thermal reservoir

  160 is provided through fixed

  conductor portion

  172 and a

  conductive coupler

  184. Melt-

  unit input contact

  174 is electrically coupled to probe-

  body input contact

  142 through fixed

  conductor portion

  172. Melt-unit

  common contact

  176 is electrically coupled to probe-body

  common contact

  144 through thermal-reservoir

  outer shell

  166,

  conductive couplers

  184, and

  coupling component

  164.

• In the preferred embodiment,

  conductive couplers

  184 are screws or pins. This is not a requirement of the present invention, however, and other means of electrical coupling may be effected without departing from the spirit of the present invention.

• Mechanical connectivity between

  thermal reservoir

  160,

  thermal insulator

  162, and

  coupling component

  164 is desirably established though the use of

  conductive couplers

  184 in the form of small-diameter, stainless steel screws. Thus,

  couplers

  184 provide mechanical and electrical coupling. In addition, since

  couplers

  184 are small in diameter and made from stainless steel they also serve as thermal insulators. But the use of pins, adhesives (not shown) or other components or methodologies to couple

  thermal reservoir

  160,

  thermal insulator

  162, and

  coupling component

  164 to form

  melt unit

  102 does not depart from the spirit of the present invention.

• FIGS. 8 and 9 show schematic views of the electrical characteristics of

  URD cable

  20 and an equivalent circuit of

  URD cable

  20, respectively, in accordance with a preferred embodiment of the present invention. The following discussion refers to FIGS. 8 and 9.

• URD cable

  20 has a

  central conductor

  22. When

  URD cable

  20 is live,

  central conductor

  22 carries current at a high voltage E_L (typically 7,200 volts). This current is coupled through a cable capacitance C to

  outer semiconductor sheath

  28. A portion of this current therefore passes through a cable resistance R to form a line signal S_L. Line signal S_L has a line-signal amplitude that is normally either very small, on the order of a few millivolts (when

  URD cable

  20 is live) or nearly zero (when

  URD cable

  20 is dead). Naturally, line signal S_L is at line frequency (normally 50-60 Hz). Line signal S_L forms across cable resistance R. Line signal S_L is therefore present at

  input contact

  150.

• FIG. 10 shows a flow chart of a

  method

  300 for determining the status of

  URD cable

  20 using

  apparatus

  100 in accordance with a preferred embodiment of the present invention. FIGS. 11 and 12 show cross-sectional side views of

  apparatus

  100 in contact with

  unjacketed URD cable

  20′ (FIG. 11) and

  jacketed URD cable

  20″ (FIG. 12) in accordance with a preferred embodiment of the present invention. FIG. 13 shows a schematic block diagram of a

  cable analysis circuit

  186 for

  apparatus

  100 in accordance with a preferred embodiment of the present invention. FIGS. 14 through 19 show a plan view of a

  status display unit

  188 for

  apparatus

  100 depicting no electrical connection (FIG. 14), a “short” or low-resistance electrical connection (FIG. 15), an “open” or high-resistance electrical connection (FIG. 16), a “dead” or de-energized cable status (FIG. 17), an “unknown” or indeterminate cable status (FIG. 18), and a “live” or energized cable status (FIG. 19) in accordance with a preferred embodiment of the present invention. The following discussion refers to FIGS. 3 and 10 through 13.

• Initially, a task 302 (FIG. 10) determines, typically through observation by a worker, if

  URD cable

  20 to be tested is

  unjacketed URD cable

  20′ (FIG. 11) or jacketed

  URD cable

  20″ (FIG. 12).

• If

  task

  302 determines

  URD cable

  20 is

  unjacketed URD cable

  20′, then, if

  melt unit

  102 is attached to probe

  body

  124, a

  task

  304′ detaches melt

  unit

  102 from

  probe body

  124.

• Next, an

  optional task

  306′ cleans unjacketed

  URD cable

  20′. Desirably,

  task

  306′ cleans unjacketed

  URD cable

  20′ through the use of a hotstick with a cleaning device attached (not shown). In this manner, the worker stays safely away from

  unjacketed URD cable

  20′.

  Task

  306′ is considered optional because it may be skipped, particularly on the first attempt at determining cable status. A worker may decide to skip

  task

  306′ if an observation of

  cable

  20′ reveals neutral conductors that do not appear to be particularly corroded. But if cable status cannot be successfully determined on the first attempt, then subsequent iterations may include

  task

  306′.

• A

  task

  308′ then positions

  active end

  120 of

  probe

  104 over a desired contact location on

  unjacketed URD cable

  20′.

• A

  task

  310′ connects

  probe

  104 to

  unjacketed URD cable

  20′ by causing

  input contact

  150 to contact

  outer semiconductor sheath

  28 and

  common contact

  152 to contact at least one of

  neutral conductors

  30. The tip of probe-body input contact 142 (serving as probe input contact 150) is substantially flat or blunt to provide a significant amount of contact area and to minimize damage to

  outer semiconductor sheath

  28.

• A

  task

  314′ then determines if

  probe

  104 has successfully established an electrical connection with

  unjacketed URD cable

  20′ in

  task

  310′. That is,

  task

  314′ determines that

  input contact

  150 contacts either

  outer semiconductor sheath

  28 or one of

  neutral conductors

  30 at the same time

  common contact

  152 contacts one of

  neutral conductors

  30. The establishment of the electrical connection is evidenced by the illumination of an “on” indicator 198 (FIGS. 13 and 15 through 19).

• It will be appreciated that

  input contact

  150 may on occasion contact one of

  neutral conductors

  30. This constitutes a “short” electrical connection, and is discussed in detail hereinafter.

• Similarly, it will be appreciated that

  input contact

  150 may on occasion not effect a good contact with

  outer semiconductor sheath

  28. This constitutes an “open” electrical connection, and is discussed in detail hereinafter.

• Apparatus

  100 incorporates cable analysis circuit 186 (FIG. 13) housed within instrumentation unit 106 (FIG. 3) and electrically coupled to input and

  common contacts

  150 and 152.

  Cable analysis circuit

  186 includes a

  power supply

  190 configured to automatically provide power to the remainder of

  cable analysis circuit

  186 when

  task

  310′ establishes the electrical connection between

  probe

  104 and

  URD cable

  20.

• Power supply

  190 contains a

  battery

  192, a

  contact detector

  194 coupled between

  battery

  192 and

  input contact

  150, and a

  gated regulator

  196.

  URD cable

  20 has cable resistance R between the point on

  outer semiconductor sheath

  28 where

  input contact

  150 makes contact and the

  neutral conductor

  30 where

  common contact

  152 makes contact. Therefore, when a electrical connection has been made, there is a complete circuit through

  battery

  192,

  contact detector

  194,

  input contact

  150, cable resistance R,

  common contact

  152, and back to

  battery

  192. When this complete circuit occurs, current flows though

  contact detector

  194, and a signal is sent to

  gated regulator

  196.

  Gated regulator

  196 then turns on and supplies regulated power to the remainder of

  cable analysis circuit

  186. This results in an “on”

  indicator

  198 of

  status display unit

  188 being activated (FIGS. 13 and 15 through 19). This auto-on feature simplifies and thereby encourages the use of

  apparatus

  100, and also prevents accidentally leaving

  apparatus

  100 turned on and unnecessarily draining

  battery

  192.

• In addition,

  battery

  192 is preferably tested prior to the use of

  apparatus

  100 to prevent errors. The auto-on feature allows

  battery

  192 to be tested by simply shorting input and

  common contacts

  150 and 152 together with a coin, a key, a tool, or any other handy piece of metal. A

  good battery

  192 will result in a “short” indication (FIG. 15) of status display unit 188 (discussed in detail hereinafter).

• Those skilled in the art will appreciate that other methods of turning on

  apparatus

  100 may be incorporated. The use of any such method, including but not limited to a simple switch, does not depart from the spirit of the present invention.

• If

  task

  314′ (FIG. 10) determines that

  probe

  104 has not established the electrical connection, i.e., “on”

  indicator

  198 is not lit, then the process flow passes back to

  task

  308′, and probe 104 is repositioned at a different contact location on

  unjacketed URD cable

  20′.

  Tasks

  308′, 310′, and 314′ are repeated.

• If

  task

  314′ determines that

  probe

  104 has established the electrical connection. i.e., “on”

  indicator

  198 is lit, then a

  task

  316′ then determines if the electrical connection is a “short” connection.

• Cable analysis circuit

  186 incorporates a connection determination circuit 200 (FIG. 13).

  Connection determination circuit

  200 is a form of dynamic ohmmeter configured to compare cable resistance R against predetermined resistance thresholds. A

  signal injector

  202 injects a trace signal S_T into

  input contact

  150. Trace signal S_T is divided between an output resistance (not shown) of

  signal injector

  202 and cable resistance R. Trace signal S_T therefore has a trace-signal amplitude that is a function of the value of cable resistance R.

• Signal injector

  202 produces trace signal S_T at a frequency different from the line frequency (usually 50 or 60 Hz) of the electric distribution system of which

  URD cable

  20 is a part. This frequency is typically higher, and is nominally 32 kHz in the preferred embodiment. Those skilled in the art will appreciate that the use of other frequencies for trace signal S_T does not depart from the spirit of the present invention.

• Trace signal S _T is amplified by a

  preamplifier

  204 and passes to the inputs of a

  first filter

  206 configured to pass trace signal S_T and a

  second filter

  208 configured to block trace signal S_T. In the preferred embodiment the

  pass filter

  206 is a high-pass filter configured to pass signals at the trace frequency (32 kHz) and block signals at the line frequency (50-60 Hz), and the

  block filter

  208 is a low-pass filter configured to block signals at the trace frequency and pass signals at the line frequency. Trace signal S_T therefore passes through high-

  pass filter

  206.

• Trace signal S _T is then applied to a pair of threshold detectors. A lower-

  threshold detector

  210 determines if the trace-signal amplitude is less than a predetermined lower trace threshold. That is, since the trace-signal amplitude is a function of the cable resistance R,

  lower threshold detector

  210 determines if cable resistance R is less than a predetermined lower resistance threshold. In the preferred embodiment, this predetermined lower resistance threshold is greater than 75 Ω, and preferably approximately 100 Ω.

• A cable resistance R of less than the lower resistance threshold results in a “short” connection, and a “short”

  indicator

  212 of status display unit 188 (FIGS. 13 and 15) is activated. Such a condition indicates that

  input contact

  150 is contacting either one of

  neutral conductors

  30 or is contacting a local shorted area of

  outer semiconductor sheath

  28.

• In either case,

  task

  316′ (FIG. 10) determines that the electrical connection is a “short” connection, i.e., the “short”

  indicator

  212 is lit. The process flow passes back to

  task

  308′ and

  apparatus

  100 is repositioned at a different contact location on

  unjacketed URD cable

  20′.

  Tasks

  308′, 310′, 314′, and 316′ are repeated.

• If

  task

  316′ determines that the electrical connection is not a “short” connection, i.e., “short”

  indicator

  212 is not lit, then a

  task

  318′ determines if the electrical connection is an “open” connection.

• A higher-threshold detector 214 (FIG. 13) determines if the trace-signal amplitude is greater than a predetermined higher trace threshold. That is, if cable resistance R is greater than a predetermined higher resistance threshold. In the preferred embodiment, this predetermined higher resistance threshold is less than 50 kΩ, and preferably approximately 30 kΩ.

• A cable resistance R of greater than the higher resistance threshold results in an “open”

  indicator

  216 of status display unit 188 (FIGS. 13 and 16) being activated. Such a condition may indicate that

  input contact

  150 is making a poor contact with

  outer semiconductor sheath

  28, or is contacting a local contaminated area of

  outer semiconductor sheath

  28, or that

  common contact

  152 is making a poor contact with

  neutral conductors

  30.

• In any of these situations,

  task

  318′ (FIG. 10) determines that the electrical connection is an “open” connection, i.e., the “open”

  indicator

  216 is lit. The process flow passes back to

  task

  306′, unjacketed URD cable is cleaned or re-cleaned, and

  apparatus

  100 is optionally repositioned at a different contact location on

  unjacketed URD cable

  20′.

  Tasks

  308′, 310′, 314′, 316′, and 318′ are repeated.

• If

  task

  318′ determines that the electrical connection is not an “open” connection, i.e., “open”

  indicator

  216 is not lit, then the electrical connection is a “good” connection, i.e., is a valid connection. The electrical connection can be a valid connection only when the electrical connection is neither a “short” nor an “open” connection, i.e., when neither “short”

  indicator

  212 nor “open”

  indicator

  216 is lit. This occurs when lower-

  threshold detector

  210 determines the trace-signal amplitude is greater than the lower trace threshold and higher-

  threshold detector

  214 determines the trace-signal amplitude is less than the higher trace threshold, i.e., cable resistance R is greater than the lower resistance threshold and less than the higher resistance threshold. In this condition a

  logic gate

  218 causes an optional “good”

  indicator

  220 of status display unit 188 (FIG. 13) being activated.

• An output of

  logic gate

  218 is used to provide condition information elsewhere in

  cable analysis circuit

  186.

• Cable analysis circuit

  186 incorporates a

  status determination circuit

  222.

  Status determination circuit

  222 is a form of a gated comparator configured to compare line signal S_L against predetermined signal thresholds. Line signal S_L is amplified by

  preamplifier

  204 and passes to the inputs of

  first filter

  206 configured to block line signal S_L and

  second filter

  208 configured to pass line signal S_L. In the preferred embodiment the

  block filter

  206 is a high-pass filter configured to block signals at the line frequency and pass signals at the trace frequency, and the

  pass filter

  208 is a low-pass filter configured to block signals at the trace frequency and pass signals at the line frequency. Line signal S_L therefore passes through the low-

  pass filter

  208.

• Line signal S _L is then applied to a pair of gated threshold detectors. The gate of each of these gated threshold detectors is coupled to

  logic gate

  218 of

  connection determination circuit

  200. This means that each of the gated threshold detectors can produce an output only if

  connection determination circuit

  200 determines that the electrical connection between

  probe

  104 and

  URD cable

  20 is a valid electrical connection, i.e., is a “good” connect wherein either optional “good”

  indicator

  220 is lit and/or both “short”

  indicator

  212 and “open”

  indicator

  216 are not lit.

• No determination of the status of

  URD cable

  20 is made unless

  connection determination circuit

  200 is simultaneously determining that the electrical connection between

  probe

  104 and

  URD cable

  20 is a valid electrical connection. This logic severely limits the potential for either a false-dead or a false-live status indication.

• If

  task

  318′ (FIG. 10) determines that the electrical connection is not an “open” connection, i.e., “open”

  indicator

  216 is not lit, then a

  task

  320′ determines if the status of

  unjacketed URD cable

  20′ is “dead” or de-energized.

• A gated lower-

  threshold detector

  224 determines if the line-signal amplitude is less than a predetermined lower signal threshold. A line-signal amplitude less than the lower signal threshold results in a “dead”

  indicator

  226 of status display unit 188 (FIGS. 13 and 17) being activated. Such a condition indicates that

  URD cable

  20 is dead, i.e., de-energized.

• This constitutes a positive test for a “dead” status for

  URD cable

  20. Such a positive dead test, where a

  de-energized URD cable

  20 is positively determined to be dead, is superior to a negative live test, where a

  de-energized URD cable

  20 is determined to be not live. A positive dead test eliminates many possible false-dead indications (where a

  live URD cable

  20 is falsely reported to be dead), whereas a negative live test does not. A false-dead status is the worst of all possible indications and creates the potential for injury or death should the worker spike or cut a

  live URD cable

  20.

• If

  task

  320′ (FIG. 10) determines that the status of

  unjacketed URD cable

  20′ is “dead” or de-energized, then flow routes to a

  terminal task

  322 wherein

  unjacketed URD cable

  20′ is indicated to be dead, i.e. “dead”

  indicator

  226 is lit (FIGS. 13 and 17).

• If

  task

  320′ determines that the status of

  unjacketed URD cable

  20′ is not “dead” or de-energized, i.e., “dead” indicator is not lit, then a

  task

  324′ determines if the status of

  unjacketed URD cable

  20′ is “live” or energized.

• A gated higher-threshold detector 228 (FIG. 13) determines if the line-signal amplitude is greater than a predetermined higher signal threshold. A line-signal amplitude greater than the higher signal threshold results in a “live”

  indicator

  230 of status display unit 188 (FIGS. 13 and 19) being activated. Such a condition indicates that

  URD cable

  20 is live, i.e., energized.

• This constitutes a positive test for a “live” status for

  URD cable

  20. A positive live test, where an

  energized URD cable

  20 is positively determined to be live, eliminates many possible false-live indications (where a

  dead URD cable

  20 is falsely reported to be live).

• If

  task

  324′ (FIG. 10) determines that the status of

  unjacketed URD cable

  20′ is “live” or energized, then an

  optional task

  326′ determines, usually by observation, if

  unjacketed URD cable

  20′ is clamped.

• Under certain conditions, a dead unjacketed URD cable will pick up enough electrical noise, perhaps in the form of stray ground currents flowing in

  neutral conductors

  30, to produce a false-live or unknown status indication. This can occur when

  neutral conductors

  30 loosely contact

  outer semiconductor sheath

  28, or when sufficient corrosion of

  neutral conductors

  30 has set in so as to cause a poor contact between

  neutral conductors

  30 and

  outer semiconductor sheath

  28 at the contact location. This condition may be improved by clamping

  neutral conductors

  30 to

  outer semiconductor sheath

  28 to break through the corrosion and otherwise short any stray ground currents to

  semiconductor sheath

  28.

• The preferred method of clamping is to use one or two hotsticks with one or two “hotstick clamps” affixed to the ends of hotsticks. In this manner, the worker stays safely away from

  unjacketed URD cable

  20′. If one clamp is used, it is desirably positioned as close to the probing area as possible. More preferably, two clamps are used, and the two clamps are positioned roughly 30 cm apart, on opposing sides of the probing area. The clamps shunt or short circuit any stray current flow down the outside of

  semiconductor sheath

  28 around the area being probed. Thus, any voltage measured in the probed area between the clamps originates from current flow at the

  center conductor

  22, via capacitance “C” (FIGS. 8-9), to

  semiconductor sheath

  28, and then to

  neutral conductors

  30. But if the cable is live, the clamps do not interfere with the measurement.

• If

  task

  326′ determines that

  unjacketed URD cable

  20′ is not clamped or that it may be inadequately clamped, then in a

  task

  328′ unjacketed URD cable is clamped or re-clamped as discussed above. Flow then passes to

  task

  308′, where

  probe

  104 is repositioned at a contact location on

  unjacketed URD cable

  20′ proximate the clamp or clamps.

  Tasks

  308′, 310′ 314′, 316′ 318, 320, 324′, and 326′ are repeated.

• If

  task

  326′ determines that

  unjacketed URD cable

  20′ is adequately clamped and indicating a live condition, then process flow routes to a

  terminal task

  330, wherein

  unjacketed URD cable

  20′ is simply indicated as being live, i.e. “live”

  indicator

  230 is lit (FIGS. 13 and 19).

• If

  task

  324′ determines that the status of

  unjacketed URD cable

  20′ is not “live” or energized, i.e., “live”

  indicator

  230 is not lit, then in a

  task

  332′ the status of

  unjacketed URD cable

  20′ cannot be determined, i.e., is “unknown” or indeterminate.

• When gated lower-

  threshold detector

  224 determines the line-signal amplitude is greater than the lower signal threshold and gated higher-

  threshold detector

  228 determines the line-signal amplitude is less than the higher signal threshold, then a

  logic gate

  232 results in an “unknown”

  indicator

  234 of status display unit 188 (FIGS. 13 and 18) being activated. Such a condition indicates that the status of

  URD cable

  20 is indeterminate. In this case, the process flow passes back to

  tasks

  326′ and 328′ where

  unjacketed URD cable

  20′ is clamped or re-clamped as discussed above.

  Tasks

  308′, 310′ 314′, 316′ 318′, 320′, 324′, and 326′ are then repeated. Presumably, a worker will repeat the above-discussed tasks as needed until a clear indication of either a “dead” or “live” cable is obtained.

• If

  task

  302 determines

  URD cable

  20 is jacketed

  URD cable

  20″, then, if

  melt unit

  102 is not attached to probe

  body

  124, a

  task

  304″ attaches

  melt unit

  102 to probe

  body

  124.

• A

  task

  306″ heats melt

  unit

  102 to the desired temperature by applying heat from

  external heat source

  181.

• A

  task

  308″ positions

  active end

  120 of

  probe

  104 over a desired contact location on

  jacketed URD cable

  20″.

• A

  task

  310″ connects

  probe

  104 to

  jacketed URD cable

  20″ by causing input and

  common contacts

  150 and 152 to melt through insulating

  jacket

  32 of

  jacketed URD cable

  20″ so that

  input contact

  150 contacts

  outer semiconductor sheath

  28 and

  common contact

  152 contacts at least one of

  neutral conductors

  30. The tip of melt-unit input contact 174 (serving as probe input contact 150) is a blunt point, but sharper than probe-

  body input contact

  142, to allow melting through

  jacket

  32 and a partial melt into the outermost portion of

  outer semiconductor sheath

  28.

  Probe

  104 is pressed against

  jacketed URD cable

  20″ until the lip or rim of

  common contact

  176 contacts one or two

  neutral conductors

  30. Due to the projection of input contact 174 a predetermined distance beyond

  contact

  176,

  input contact

  174 will only slightly penetrate into

  semiconductor sheath

  28 when

  contact

  176 abuts

  neutral conductors

  30. With

  contact

  176 projecting around 2.5 mm beyond

  common contact

  174, sufficient, but not excessive, penetration into

  semiconductor sheath

  28 results when

  cable

  20″ has 10-14 gage

  neutral conductors

  30. When larger or smaller diameter

  neutral conductors

  30 are encountered, then input

  contact

  174 is replaced by a longer or

  shorter input contact

  174, as needed.

• A

  task

  312″ determines, typically through observation, if

  task

  310″ successfully melted

  melt unit

  102 into insulating

  jacket

  32, i.e., if

  melt unit

  102 was hot enough.

• If

  task

  312″ determines that

  melt unit

  102 was not hot enough (i.e., there was a bad melt), then the process flow passes back to

  task

  306″ and

  melt unit

  102 is reheated.

  Tasks

  306″, 308″, 310″, and 312″ are repeated.

• A

  task

  314″ then determines if

  probe

  104 has successfully established an electrical connection with

  jacketed URD cable

  20″ in

  task

  310″ as discussed hereinbefore for

  task

  314′.

• If

  task

  314″ determines that

  probe

  104 has not established the electrical connection, i.e., “on”

  indicator

  198 is not lit, then the process flow passes back to

  task

  308″ and probe 104 is repositioned at a different contact location on

  jacketed URD cable

  20″.

  Tasks

  308″, 310″, 312″, and 314″ are repeated.

• If

  task

  314″ determines that

  probe

  104 has established the electrical connection. i.e., “on”

  indicator

  198 is lit, then a

  task

  316″ determines if the electrical connection is a “short” connection as discussed hereinbefore in connection with

  task

  316′.

• If

  task

  316″ determines that the electrical connection is a “short” connection, i.e., the “short”

  indicator

  212 is lit, then the process flow passes back to

  task

  308′ and

  apparatus

  100 is repositioned at a different contact location on

  jacketed URD cable

  20″.

  Tasks

  308″, 310″, 312″, 314″, and 316″ are repeated.

• If

  task

  316″ determines that the electrical connection is not a “short” connection, i.e., “short”

  indicator

  212 is not lit, then a

  task

  318″ determines if the electrical connection is an “open” connection as discussed hereinbefore in connection with

  task

  318′.

• If

  task

  318″ determines that the electrical connection is an “open” connection, i.e., the “open”

  indicator

  216 is lit, then the process flow passes back to

  task

  308″ and

  apparatus

  100 is repositioned to a different contact location on

  jacketed URD cable

  20″.

  Tasks

  308″, 310″, 312″, 314″, 316″, and 318″ are repeated.

• If

  task

  318″ determines that the electrical connection is a “good” or valid connection, then a

  task

  320″ determines if the status of

  jacketed URD cable

  20″ is “dead” or de-energized as discussed hereinbefore in connection with

  task

  320′.

• If

  task

  320″ determines that the status of

  jacketed URD cable

  20″ is “dead”, then flow routes to

  terminal task

  322 wherein

  jacketed URD cable

  20″ is indicated to be dead, i.e. “dead”

  indicator

  226 is lit.

• If

  task

  320″ determines that the status of

  jacketed URD cable

  20″ is not “dead” or de-energized, i.e., “dead” indicator is not lit, then a

  task

  324″ determines if the status of

  jacketed URD cable

  20″ is “live” or energized as discussed hereinbefore in connection with

  task

  324′.

• If

  task

  324″ (FIG. 10) determines that the status of

  jacketed URD cable

  20″ is “live” or energized, then flow routes to a

  terminal task

  330 wherein

  jacketed URD cable

  20″ is indicated to be live, i.e. “live”

  indicator

  230 is lit.

• If

  task

  324″ determines that the status of

  jacketed URD cable

  20″ is not “live” or energized, i.e., “live”

  indicator

  230 is not lit, then in a

  task

  332″ the status of

  jacketed URD cable

  20″ cannot be determined, i.e., is “unknown” or indeterminate as discussed hereinbefore. In this case, the process flow passes back to

  task

  308″ and

  apparatus

  100 is repositioned to another contact location on

  jacketed URD cable

  20″.

  Tasks

  308″, 310″, 312″, 314″, 316″, 318″, 320″, and 324″ are repeated.

• Terminal tasks

  322 and 330, for “dead” and “live” statuses respectively, represent the end or termination of a successful status determination effort. However, even though

  apparatus

  100 is carefully structured to minimized the possibility of either a false-dead or a false-live status indication, there is always a chance that such an error might occur. The presence of such an error, especially a false-dead indication, may pose a hazard and incur a risk of injury or death. To further reduce any chance of injury or death,

  terminal tasks

  322 and 330 should be followed by a

  task

  334 wherein the entire

  status determination method

  300 is repeated with

  apparatus

  100 positioned at a different contact location on

  URD cable

  20. After a plurality of such status determination procedures, the assurance that

  URD cable

  20 is truly dead or live approaches certainty. The ease with which

  apparatus

  100 may be used to perform

  status determination method

  300 encourages repeated performances of

  method

  300.

• The following discussion refers to FIGS. 3 and 13 through 19.

• Status display unit

  188 contains a plurality of indicators 236 coupled to

  display side

  118 of

  instrumentation unit

  106.

• By using a plurality of indicators 236, sufficient information is imparted to the worker to make an informed and safe decision regarding the status of

  URD cable

  20. In the preferred embodiment, indicators 236 include “on”

  indicator

  198 to indicate an electrical connection is established between

  probe

  104 and

  URD cable

  20, “short”

  indicator

  212 to indicate that the electrical connection is a “short” connection and not a valid connection, “open”

  indicator

  216 to indicate that the electrical connection is an “open” connection and not a valid connection, “dead”

  indicator

  226 to indicate that

  URD cable

  20 is de-energized when the electrical connection is a valid connection, “live”

  indicator

  230 to indicate that

  URD cable

  20 is energized when the electrical connection is a valid connection, and “unknown”

  indicator

  234 to indicate that the status of

  URD cable

  20 cannot be determined. In an alternative embodiment, “good” indicator may be used in conjunction with or in lieu of “short” and “open”

  indicators

  212 and 216 to indicate that the electrical connection is a valid connection.

• Indicators 236 are placed on

  display side

  118 of

  instrumentation unit

  106 so as to be in the worker's line of sight while the worker is establishing contact with and determining the status of

  URD cable

  20. In the preferred embodiment, indicators 236 are visual indicators, preferably light-emitting diodes.

• In the preferred embodiment, indicators 236 are patterned in two rows or lines. A first line of indicators 236 contains “short”

  indicator

  212, “on”

  indicator

  198, and “open”

  indicator

  216, i.e., those indicators 236 associated with

  condition determination circuit

  200. A second line of indicators 236 contains “dead”

  indicator

  226, “unknown”

  indicator

  234, and “live”

  indicator

  230.

• In the preferred embodiment, “dead”

  indicator

  226 is of a first color, preferably green, “live” indicator is of a second color different from the first color, preferably red, and the remaining indicators 236 are of a third color different from either the first or second colors, preferably yellow. By using this color scheme, instantaneous and distinct interpretation of the indicated status of

  URD cable

  20 by the worker is possible.

• In addition, “short”

  indicator

  212, “open”

  indicator

  216, and “unknown”

  indicator

  234 are oriented relative to “on”

  indicator

  198 so that again instantaneous and distinct interpretation by the worker is possible.

• In summary, the present invention teaches an

  apparatus

  100 for determining the status of an underground residential distribution (URD)

  cable

  20.

  Apparatus

  100 actively determines status for both a live and a

  dead URD cable

  20.

  Apparatus

  100 determines status for both unjacketed and

  jacketed URD cables

  20′ and 20″. Apparatus displays results viewable and instantly interpretable at a distance. Apparatus determines a quality of connection to

  URD cable

  20 while determining the status thereof.

• Although the preferred embodiments of the invention have been illustrated and described in detail, it will be readily apparent to those skilled in the art that various modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.