(12) United States Patent (10) Patent N0.: US 6,493,200 B1 Farmer et al. (45) Date of Patent: Dec. 10, 2002

Transcription

1 i US B1 (12) United States Patent (10) Patent N0.: US 6,493,200 B1 Farmer et a. (45) Date of Patent: Dec. 10, 2002 (54) COAXAL CABLE PROTECTON DEVCE Primary Examiner EdWard H. Tso _ Assistant Examiner Pia Tibbits (75) nventors: James 0. Farmer, Liburn; Keith Feming, Jonesboro, both of GA (US) (57) ABSTRACT (73) Assignee: Arris nternationa nc" Duuth GA This invention provides improved methods of protection (Us) required under the 1999 edition of the Nationa Eectric ( * ) Notice: Subject to any discaimer, the term of this Code, section NEC 830 requirement that if a drop coaxia patent is extended or adjusted under 35 cabe (usuay suppying an individua residence) carries U.S.C. 154(b) by 130 days. power above a certain votage, it must incude suf?cient protection from eectric shock for peope Who may come in (21) App- NO- 09/684,131 contact With it. A drop coaxia cabe Woud be carrying (22) Fied, Oct suf?cient power for NEC 830 protection if it Were suppying a cabe teephone interface box or other AC powered net Reated US- Appication Data Work interface devices. n one embodiment, the invention (60) Provisiona appication NO- 60/158353?ed on Oct- 8 utiizes the AC power signa from the drop cabe to operate an AC power sensing circuit. The circuit utiizes an upper (51) nt. C H02H 1/00 and ower Current range to determine Whether to activate a U-S- C Switch Operative to interrupt the power in the drop Cabe~ of Search , one Variation of the invention utiizes an Osciator gener_ 361/42, 45, 49, 93, 107, 108; 333/206 ated probe signa to determine if there is a vaid circuit (56) References Cited connection. Another variation of the invention utiizes an osciator driven AC power insertion circuit to determine if US PATENT DOCUMENTS there is a vaid circuit connection. The invention aows RF 5,768,084 A * 6/1998 Chaudhry et a /113 signas to continue transmitting unimpeded, 5,930,100 A * 7/1999 Gasque, Jr. et a /117 * cited by examiner 21 Caims, 8 Drawing Sheets Current (ma) Output to drop nput from t1 (drop S'de) 250 (tap side) Maximum currentdraw 200 (triac cosed) _ O Power Suppy 100 Threshod DUB 1 Detector 1 00 _ /. Triac Switch Minimum current draw triac cosed) Characteristic Chart Maximum and minimum, triac open (triac wi cose if current is between max and min.) Suppy Votage (vots)

2 U.S. Patent Dec. 10, 2002 Sheet 1 0f 8 US 6,493,200 B1 Output to drop 106. nput from tap E (drop sde) (tap side) 112 = - _ D 108 v AD ' T355213? T WT \122 / 124 \ Triac Switch v ) a : L_ca_o(up _ so) _L_ _, ' 120 : a e Power Suppy 100 _ J Fig. 1A

3 U.S. Patent Dec. 10, 2002 Sheet 2 0f 8 US 6,493,200 B1 Current (ma) 300 Characteristic Chart Maximum current draw 200 (triac cosed) 150 Tra_c remans cosed Minimum current draw (triac cosed) 0 4o / Maximum and minimum, triac open (triac wi cose if current is between max and min.) Suppy Votage (vots) Fig. 1B

4 U.S. Patent Dec. 10, 2002 Sheet 3 0f 8 US 6,493,200 B1 nput from tap (tap side) Power Suppy 100. : 218 fp trap ] 216 / (RF bypass) \ Triac Switch v. '/ (x 200 fp (probe signa generator) J SD2 WdO m 068 ham v0 Output to drop nr v A mo (drop side) W m To DMQZZ S wsm4 1 ht o mm J Fig. 2A

5 U.S. Patent Dec. 10, 2002 Sheet 4 0f 8 US 6,493,200 B1 fp trap nput from drop ' ' ' Td ND (drop side) (premse sde) / \. _ fp bandpass : :226 ' _ J 228 Fig. 2B

6 U.S. Patent Dec. 10, 2002 Sheet 5 0f 8 US 6,493,200 B1 _ RF Bypass nput from tap / (tap side) ' \ J :3 Triao Switch 3 * / 304 Microprocessor Output to drop (drop side) Fig. 3A

7 U.S. Patent Dec. 10, 2002 Sheet 6 0f 8 US 6,493,200 B1 nput from drop f! To ND (drop side) \ (premise side) Q Fig. 3B

8

9 U.S. Patent Dec. 10, 2002 Sheet 8 0f 8 US 6,493,200 B1 triac 400 A 410 m & Contro signa from dua 4' threshod detector V Fig. 4B

10 1 COAXAL CABLE PROTECTON DEVCE FELD OF NVENTON This invention reates to the?ed of eectrica circuits and, more speci?cay, to providing the protection required under the 1999 edition of the Nationa Eectric Code, section 830. This invention caims priority over provisiona appication No. 60/158,453?ed Oct. 8, BACKGROUND NEC830 deas With requirements for broadband commu nication systems, such as cabe teevision systems, Which provide powering on, or attached to, the coaxia cabe on Which signas are transmitted to bring, for exampe, teevi sion programs and other services to subscribers. Coaxia cabe usuay runs from a device caed a tap, Which extracts a portion of the power from the distribution coaxia cabe, to a subscriber s buiding or residence, hereinafter referred to simpy as the subscriber. This coaxia cabe is caed the drop. NEC830 requires that if the drop carries power above a certain votage, it must meet certain require ments for the protection of peope Who may come in contact With it. The most common reason the drop Woud be carrying power is to suppy a cabe teephone interface box, or network interface device (ND). The requirements of NEC830 are that the drop must meet certain physica requirements, or it must be protected by a UL isted faut protection device, to detect if a drop is either shorted or open and, in either case, interrupt power carried in the drop unti the faut has ceared. Broadband services, such as cabe teephony appications, may require AC power to be suppied from the tap cabe to the drop cabe. The coaxia cabe drop to the subscriber is therefore AC hot and subjects the instaer or other craftspersons Working With the cabe drop to potentia eectrica shock and/or eectrocution. An exampe of an NEC830 safety circuit for interrupting AC power on the drop cabe is described in US. Pat. No. 5,793,590 to Vokey et a. The device described in Vokey is a two-unit device having a tap unit and a premise unit. An independent DC power source is used to power the two-unit device and to provide a probe votage. A dua threshod detector compares a DC votage drop proportiona to the AC power transferred to the drop cabe With a probe votage to determine Whether there is a short or open condition at the junction of the tap and drop cabes. Whie Vokey is suitabe for its genera purpose, it utiizes an anaog methodoogy that can ack ong-term caibration dependabiity in harsh environmenta conditions. Aso, the imitations of monitor ing a DC votage drop proportiona to the AC power transferred to the drop cabe tends to make the Vokey methodoogy inaccurate because the monitored DC votage drop is merey an approximation of the actua AC power transferred to the drop cabe. n addition, the second (DC) power source creates certain inefficiencies. A capacitor must keep the DC power source separate from the AC power signas in the drop cabe and thus is critica for the operation of the safety device as a Whoe. This capacitor s necessariy arge physica size makes it cumbersome for circuit pack aging. Capacitors of this size are avaiabe, but aong With being arger than one Woud ike in this appication, getting one With an adequate current rating and good ong term reiabiity in an outdoor (but shetered) environment is dif?cut. Thus, for an ef?cient and reiabe safety device soution it Woud be desirabe to eiminate the need for arge vaue capacitors and to have a precise, rather than approximate, monitoring capabiity. US 6,493,200 B SUMMARY OF THE NVENTON The present invention overcomes the above-described probems in the prior art by providing a coaxia cabe safety device that utiizes the AC power aready present in a drop cabe as a powering and monitoring soution to provide a parameter indicative of such AC power. The present inven tion is a coaxia cabe protection system for a cabe media environment that incudes a primary cabe and a drop cabe having?rst and second conductors. The?rst and second conductors carry AC power and RF signas to a network interface device. The present invention incudes a?rst circuit component for aowing the RF signas to be trans mitted from the primary cabe to the?rst conductor of the drop cabe. A second circuit component features an active state for passing the AC power from the primary cabe to the?rst conductor of the drop cabe and a bocking state for seectivey bocking the passage of AC power to the?rst conductor. Asensor actuates the second circuit component to bock AC power from the?rst conductor if the current drawn between the?rst and second conductors is outside of a prescribed range. A variation of the present invention is a sensing circuit utiizing the resistance in a drop cabe. An osciator gener ates a probe frequency. A comparator compares the resis tance in a conductor With a known resistance. The known resistance is proportiona to the probe frequency. An actuator opens and coses a circuit component for bocking AC power from passing to the drop cabe based on the comparison of the drop cabe resistance provided by the comparator With the known resistance. Another variation of the present invention uses a fre quency generation and detection circuit that monitors the drop cabe for a tone signa. The drop cabe has a?rst end and a remote end. An osciator utiizes the AC signa from the drop cabe to generate a tone signa. Acircuit component actuated by the osciator Wi bock AC power in the drop cabe if the osciator does not generate a tone signa and Wi aow the AC power to pass if osciator generates a tone signa. BREF DESCRPTON OF DRAWNGS FG. 1A is a circuit diagram that iustrates an exempary environment suitabe for impementing various embodi ments of the present invention Which utiizes AC power from the drop cabe for an improved sensing technique. FG. 1B is a characteristic chart that iustrates an exem pary embodiment of the present invention. FG. 2A is a circuit diagram that iustrates an exempary environment suitabe for impementing various embodi ments of the present invention Which utiizes an osciator for an improved sensing technique. FG. 2B is a circuit diagram that iustrates an exempary environment suitabe for impementing various embodi ments of the present invention Which utiizes a bandpass?ter and trap circuit for an improved sensing technique. FG. 3A is a circuit diagram that iustrates another exempary environment suitabe for impementing various embodiments of the present invention Which utiizes AC power from the drop cabe for an improved sensing tech nique. FG. 3B is a circuit diagram that iustrates another exempary environment suitabe for impementing various embodiments of the present invention Which utiizes an osciator for an improved sensing technique. FG. 4A is a circuit diagram that iustrates an exempary environment suitabe for impementing a triac switch.

11 3 FG. 4B is a circuit diagram that iustrates another exempary environment suitabe for impementing a triac switch. DETALED DESCRPTON Referring now in detai to the drawings in Which ike numeras refer to ike parts throughout the severa views, FG. 1A is a circuit diagram that iustrates an exempary environment suitabe for impementing various embodi ments of the present invention Which utiizes AC power from the drop cabe for an improved sensing technique. FG. 1A shows the?rst teaching of this discosure Which utiizes the AC power aready present in a drop cabe to power a safety circuit. n this impementation, the current being drawn by the ND is measured by the device, Which is programmed for a reasonabe spread over and above the known current consumption range of the device. The actua current consumed is measured, and if it does not fa Within a WindoW of acceptabe vaues, a triac switch 110 is opened. f the triac switch 110 is opened, then a sma current is provided through a resistor 108 to permit sensing, so that the circuit Wi know When to cose the triac switch 110 again. Acapacitor 106 serves as an RF bypass, and has no effect on the powering issues. PoWer passes through inductor chokes 102 and 104 and normay through the triac switch 110 on its Way to the drop. The current aso passes through the primary of a current sense transformer 112. Those skied in the art know that if one buids such transformer 112 With a high turns ratio and terminates it correcty With a resistor 114, the votage on the secondary Wi be proportiona to the current in the primary, yet there Wi be itte votage drop on the primary. (Though not shown, it is sometimes desirabe to use a capacitor in the secondary to tune the transformer to the ine frequency. Those skied in the art understand the subteties.) This votage on the secondary is converted to DC by a diode 116 and capacitor 118 combination, and the DC anaog is suppied to a?rst anaog-to-digita (A/D) converter 122, Which ideay is interna to the microcontroer 120. Because the current consumption pro?e of the ND is a function of the input votage eve, it is aso necessary to measure the input votage, Which typicay can be between 40 and 90 vots AC. This measurement is made in the diode and capacitor circuit combination, 130 and 132 respectivey, and inputted to the second A/D converter 124. The micro controer 120 thus has two pieces of information on Which to base a decision to open the triac switch 110 or not. One piece of information is the current being drawn by the ND, converted in the?rst A/D converter 122, and the other is the suppy votage, converted in the second AD converter 124. FG. 1B is a characteristic chart that iustrates an exem pary embodiment of the present invention. The character istic chart 130 shows a current vs. votage pro?e for a typica four ine voice port ND. Four ine voice port NDs interface one to four teephone ines in a house to the drop cabe. More current is drawn When the phones are ringing than When they are on-hook and not being used. The difference between the maximum and minimum current curves on the characteristic chart 130 is the difference between a four ines ringing one phone each, and a four ines being on-hook (not being used). The ook-up tabe component in the microcontroer 120 reads the suppy votage, the horizonta axis in the charac teristic chart 130. From that, it is programmed to provide the appropriate imits of the maximum and minimum curves to a dua threshod detector 128, Which is impemented in software in this embodiment of the invention. So ong as the US 6,493,200 B current measured and converted by the A/D converter 122 is Within this range, the triac switch 110 remains cosed, suppying power to the ND. f the current fas outside of this range, then either there is a short circuit or there is an open circuit, so the microcontroer 120 opens the triac switch 110, removing power from the drop. f the triac switch 110 is open, then some sma current is deveoped through the probe resistor 108. This is necessary in order to probe the drop circuit, so that the system Wi know When the drop is propery connected and triac switch 110 shoud be cosed. ShoWn at the bottom of the charac teristic chart 130 are two curves Which de?ne the maximum and minimum current range expected When the triac switch 110 is open and some current has been deveoped through the probe resistor 108. When the current fas between these two curves, then the microcontroer 120 concudes that the circuit is propery made, and it coses the triac switch 110. After that, it monitors Within the upper curves of the characteristic chart 130, to make sure the current stays Within the prescribed imits. t is possibe to impement this embodiment Without using a microcontroer, but the simpicity and versatiity inherent in microcontroer contro makes the microcontroer very attractive. Using the microcontroer, it is feasibe to provide additiona features such as opening the switch quicky if a very arge over-current is detected, but opening after a deay for a sma over-current. This Woud protect against a situation Where a phone ine With many phones Was ringing. Aso, a sow start feature can be programmed, in Which once the current enters the triac open range, power is not appied for severa seconds. This Wi protect against appying power When a craftsperson is sti making connections. FG. 2A is a circuit diagram that iustrates an exempary environment suitabe for impementing various embodi ments of the present invention Which utiizes an osciator for an improved sensing technique. Asigna is generated and suppied to a ND-end circuit, and the resuting current is measured to determine if there is a vaid circuit connection. This embodiment uses a reativey high frequency signa, Which can be bocked With sma inductors and capacitors. Suitabe frequencies ie between roughy 1 khz and 1 MHZ. An osciator, 200, generates a probe signa at frequency fp. This signa is?tered in the fp bandpass?ter 202, and appied to the output of the drop. t?ows through the primary of the current sense transformer 204. This trans former is identica in function and simiar in construction to that of the transformer 112 in FG. 1A. The difference is that it operates at a much higher frequency, so it can be made even smaer. As described above, the transformer 204 is constructed With a high ratio of secondary to primary turns. The secondary output votage appearing across the resistor 206 is proportiona to the probe-frequency current in the drop (fp). The secondary of the transformer 204 may or may not be tuned to fp. The AC votage across the resistor 206 is demoduated in the synchronous detector 208. t is possibe to use an enveope detector as in FG. 1A, but the synchro nous detector 208 aows simper?tering of the recovered signa. The synchronous detector 208 is driven from a sampe of the output of the osciator 200. The resistor 206 and the capacitor 212 provide?tering on the detected signa. The DC votage appearing across the capacitor 212 is thus proportiona to the current in the drop due to the osciator s 200 excitation of the drop at a frequency of fp. A dua threshod detector 214 is used to determine if the current is Within prescribed imits. f so, then the dua threshod detector 214 coses the triac switch, aowing power to be appied to the ND. f the current is not Within

12 5 prescribed imits, indicating either a short or open on the drop, the triac switch is opened and power does not How to the ND. The fp trap 216 isoates the suppy circuit coming from the tap, from the probe signa. n FG. 1A the probe signa is a DC signa, Whereas in FG. 2A it is a high frequency signa. To isoate it, the fp trap 216 is a parae L-C circuit resonate at fp. This provides a high frequency of fp, Whie providing a ow impedance at the much ower power frequency. TWo inductors, 218 and 220, are sma radio frequency chokes used to keep the RF signas being couped through the capacitor 222 from the probe circuitry. This heps improve return oss through the circuit. FG. 2B is a circuit diagram that iustrates an exempary environment suitabe for impementing various embodi ments of the present invention Which utiizes a bandpass?ter and trap circuit for an improved sensing technique. FG. 2B shows the circuitry at the ND-end of the drop. The fp trap 224 isoates the probe signa from the ND, and fp bandpass 226 coupes the probe signa to the Resistor 228, Which sets the probe current vaue. Thus, this embodiment uses sma L-C circuits Which offer no materia impedance to the power current on the drop. This increases the votage reaching the ND, improv ing ef?ciency With switching power suppies. n addition, space and cost are saved, and the reiabiity of the circuit is enhanced by removing the need for arge eectroytic capaci tors carrying fairy substantia current. FG. 3A is a circuit diagram that iustrates another exempary environment suitabe for impementing various embodiments of the present invention Which utiizes AC power from the drop cabe for an improved sensing tech nique. n this embodiment, a customer premises equipment (CPE) termina 306 and a tap equipment (TE) termina 300, Which are connected to the subscriber side and tap side of the drop cabe. An exampe of a CPE termina 306 circuit that can be used in impementing the present invention is shown in FG. 3B beow. The TE termina 300 receives AC power from the coaxia cabe upstream of the TE termina 300 and generates a DC votage that is put on the drop cabe and detected by the osciator 308 of the CPE termina 306. The osciator 308 of the CPE termina 306 detects the DC votage and generates a tone that is put on the center conductor of the drop cabe. The TE termina 300 detects and monitors the tone on the center conductor of the drop cabe provided by the osciator 308 in the CPE termina 306. A controer 304 in the TE termina 300 monitors the ampitude of the frequency signa for step changes in ampitude that is indicative of a faut condition of the drop cabe. The controer 304 in the TE termina 300 is preferaby an inexpensive microprocessor used for detection of the frequency signa and for controing the triac switch 302. f the drop cabe is disconnected from the CPE termina 306, the frequency signa is no onger present, so the TE termina detects no tone and the micro processor 304 contros a triac switch 302 to turn off the AC votage on the drop cabe. f the drop cabe is shorted out anywhere aong its ength, the frequency signa is no onger present, so the TE termina 300 detects no tone and the microprocessor 304 contros a switch to turn off the AC votage on the drop cabe. f the drop cabe is opened anywhere aong its ength, the frequency signa is no onger present, so the TE termina 300 detects no tone and the microprocessor 304 contros a switch to turn off the AC votage on the drop cabe. The microprocessor 304 aso detects changes in the ampitude of the tone signa to aow US 6,493,200 B the monitoring of ma step changes of the insertion oss of the drop cabe, Which indicates a faut condition of the drop cabe. The microprocessor 304 may aso monitor the DC current on the drop cabe to detect step changes in current that indicates a faut condition has occurred, but this is not necessary for the operation of the invention as described above. FG. 3B is a circuit diagram that iustrates another exempary environment suitabe for impementing various embodiments of the present invention Which utiizes an osciator for an improved sensing technique. The CPE termina 306 has a circuit for directing a DC votage, generated by the TE termina 300 and provided over the drop cabe, to a ow frequency osciator 308 Whie bocking the AC signa and Whie bocking the RF payoad information signa on the drop cabe. The indicators and capacitors shown in the CPE termina 306 accompish this function. When the osciator 308 receives the DC votage, it produces a frequency tone that is paced on the drop cabe. The tone is set at a ow frequency, such as 10 khz for exampe, athough any other suitabe frequency can be used. FG. 4A is a circuit diagram that iustrates an exempary environment suitabe for impementing a triac switch. When it is desired to cose the triac switch 110, current is suppied to an LED 406, Which is part of opto-isoator 408. This current causes an optica emission from the LED 406, Which excites an optica triac 402. n turn this optica triac 402 suppies a switching votage to another triac 400, Which is the actua device that coses to permit power to pass. FG. 4B is a circuit diagram that iustrates another exempary environment suitabe for impementing a triac switch. FG. 4B shows Where an osciator 414, for exampe, the fp generator of FG. 2A, drives the triac 400 directy through a transformer 410. A variation of this is to use a bocking osciator. Frequenty an extra feedback Winding on the transformer 410 is used to provide feedback to the osciator. Other means of achieving the switch function Wi be obvious to those skied in the art. One particuary advan tageous switch means is to use a mechanica atching reay. The reay Wi not exhibit any votage drop in the signa path, and atching reays don t consume power When they are in a set state. Furthermore, reiabiity is improved because if circuitry fais, the reay Wi remain in its ast position. Whie this invention has been described in detai With particuar reference to preferred embodiments thereof, it Wi be understood that variations and modi?cations can be effected Within the scope of the invention as de?ned in the appended caims. What is caimed is: 1. A coaxia cabe protection system incuding a primary cabe and a drop cabe having?rst and second conductors for carrying AC power and RF signas to a network interface device, said system comprising: a?rst circuit component for passing the RF signa from said primary cabe to the?rst conductor of said drop cabe; a second circuit component With an active state for passing the AC power from said primary cabe to the?rst conductor of said drop cabe and a bocking state for seectivey bocking the passage of the AC power to the?rst conductor of said drop cabe; and a sensor operative to actuate the second circuit component to bock AC power from said primary cabe to the?rst conductor of said drop cabe if the current drawn between the?rst conductor and the second conductor of said drop cabe is outside of a prescribed range.

13 7 2. The coaxia cabe protection device of caim 1, Wherein the sensor is an AC power sensing circuit Which utiizes the AC power signa from the drop cabe to power said AC power sensing circuit. 3. The coaxia cabe protection device of caim 1, Wherein the sensor incudes a prescribed upper and ower current range, said current range and the AC power signa from the drop cabe utiized by said sensor to determine if the current drawn between the?rst conductor and the second conductor of said drop cabe is outside of said current range. 4. The coaxia cabe protection device of caim 1, Wherein the sensor is a microprocessor impementing a dua thresh od detector Which utiizes the AC power signa from the drop cabe. 5. The coaxia cabe protection device of caim 1, Wherein the second circuit component is a triac switch. 6. A method for seectivey bocking AC power from being transferred from a source to a conductor, said method comprising: providing AC power from said source to the conductor; measuring said AC power in said conductor to determine a measured vaue; comparing said AC power in said conductor With a predetermined range; terminating the transfer of said AC power to said con ductor if said measured vaue is outside of said prede termined range; and enabing said AC power to transfer to said conductor if said measured vaue is Within said predetermined range. 7. Asensing circuit, Wherein the resistance in a conductor can be obtained to seectivey bock an AC power signa in said conductor, said sensing circuit comprising: a comparator operabe to compare the resistance in said conductor With a known resistance utiizing the AC power signa from said conductor; and an actuator operabe to open and cose a circuit compo nent to bock the AC power signa in said conductor based on said comparison of the resistance in said conductor provided by said comparator With said known resistance. 8. The sensing circuit of caim 7, Wherein the comparator utiizes a dua threshod detector to compare the resistance in a conductor With a known resistance. 9. The sensing circuit of caim 7, Wherein the comparator utiizes a ook-up tabe to compare the resistance in a conductor With a known resistance. 10. The sensing circuit of caim 7, Wherein such circuit is impemented by a microprocessor. 11. The sensing circuit of caim 7, Wherein the actuator is impemented by an opto-isoator. 12. A method for bocking AC power in a conductor utiizing the resistance in said conductor, said method com prising: measuring the resistance in said conductor; comparing the resistance in said conductor With a known resistance utiizing the AC power signa from said conductor; and actuating a circuit component to bock the AC power signa in said conductor based on said comparison of the resistance in said conductor provided by said com parator With said known resistance. 13. A sensing circuit for bocking AC power in a conductor, utiizing the resistance in said conductor, said sensing circuit comprising: an osciator operabe to generate a probe frequency; a comparator operabe to compare the resistance in a conductor With a known resistance proportiona to said probe frequency; and US 6,493,200 B an actuator operabe to open and cose a circuit compo nent based on said comparison of the resistance in said conductor provided by said comparator With said known resistance. 14. The sensing circuit of caim 13, Wherein the com parator utiizes a prescribed upper and ower current range, said current range and the probe frequency utiized by said comparator to determine if the current drawn between the?rst conductor and the second conductor of said drop cabe is outside of said current range. 15. The sensing circuit of caim 13, Wherein the actuator is driven by said osciator. 16. A method for bocking AC power in a conductor utiizing the resistance in said conductor, said method com prising: generating a probe frequency; comparing the resistance in said conductor With a known resistance proportiona to said probe frequency; and actuating a circuit component based on said comparison of the resistance in said conductor provided by said comparator With said known resistance. 17. A tone sensing circuit, Wherein a drop cabe is monitored for a generated tone signa, comprising: an osciator, driven by the AC power from said drop cabe, operabe to generate a tone signa; a controer operabe to monitor said drop cabe for said generated one signa; and an actuator operabe to open and cose a circuit compo nent to bock AC power in said drop cabe based on Whether said controer detects a tone signa. 18. The tone sensing circuit of caim 17, Wherein the controer is operabe to detect a change in ampitude of said generated tone signa. 19. The tone sensing circuit of caim 17, Wherein the actuator is operabe to open and cose a circuit component to bock AC power in said drop cabe based on Whether said controer detects a change in ampitude of said generated tone signa. 20. A method for detecting a faut condition in a conductor, said method providing a conductor having a?rst end and a remote end, said method comprising: transferring AC power aong said conductor from the?rst end to the remote end; ocating an osciator at the remote end of said conductor operabe to utiize said AC power for generating a tone signa; detecting said generated tone signa; and actuating a circuit component to bock said AC power in said conductor When said generated tone signa is not detected. 21. A method for seectivey bocking AC power from being transferred from a source to a conductor, said method comprising: providing AC power from said source to the conductor; measuring a parameter indicative of said AC power in said conductor to determine a measured vaue; comparing said parameter indicative of said AC power in said conductor With a predetermined range; terminating the transfer of said AC power to said con ductor if said measured vaue is outside of said prede termined range; and enabing said AC power to transfer to said conductor if said measured vaue is Within said predetermined range.