Electrical safety device with conductive polymer sensor

• US 5,862,030 A
• Filed: 06/02/1998
• Issued: 01/19/1999
• Est. Priority Date: 04/07/1997
• Status: Expired due to Fees

• Current Assignee: Electro-TK, Inc.
• Original Assignee: BPW, Inc.
• Inventors: Watkins, Kenneth S. Jr., Morris, Shelby J. Jr.
• Primary Examiner(s): Gaffin, Jeffrey
• Assistant Examiner(s): SHERRY, MICHAEL JUDE
• Application Number:
  US09/089,037
• Time in Patent Office: 231 Days
• Field of Search: 361/103, 361/106, 361/93, 219/110, 219/241, 219/485, 219/491, 219/494, 219/497, 219/510, 174/102 R, 174/103, 174/104, 174/105 R, 174/107, 174/110 R, 174/128.2, 174/138 J
• US Class Current: 361/103
• CPC Class Codes: H02H 5/043 the temperature dependent resistor being disposed parallel to a heating wire, e.g. in a heating blanket
• CPC Class Codes: H02H 7/228 for covered wires or cables

Abstract

An electrical safety device comprises a sensor strip disposed in the insulation of a wire or in the insulation of a sheath enclosing a bundle of insulated electrical conductors. The sensor strip comprises a distributed overtemperature sensing portion comprising a conductive polymer having a positive temperature coefficient of resistivity which increases with temperature sufficient to result in a switching temperature. A mechanical damage sensing portion comprises a strip disposed in the sheath in a mechanical damage sensing pattern which becomes damaged or open upon mechanical damage of the sheath before the bundle of conductors are damaged. The overtemperature sensing portion and the mechanical damage sensing portion may be the same sensing strip disposed in the sheath and arranged in a helical relationship with a longitudinal axis of the sheath.

Claims

1. A sheath for providing overtemperature and mechanical damage sensing for a of electrical conductors, the sheath comprising:

a layer of insulative material positionable to substantially surround said plurality of electrical conductors; and

at least one sensor strip in communication with the layer of insulative material and made of a conductive polymer material comprising a positive temperature coefficient of resistivity which increases with temperature, said at least one sensor strip extending a length of said plurality of electrical conductors and disposed between an outside surface of the sheath and said plurality of electrical conductors so that mechanical damage originating on the outside surface will result in mechanical damage to said at least one sensor strip before mechanical damage is sustained to said plurality of electrical conductors.

2. The sheath of claim 1 wherein the positive temperature coefficient of resistivity increases at a rate with temperature so as to result in a switching temperature.

3. The sheath of claim 2 wherein said at least one sensor strip is disposed in a helical pattern with respect to a longitudinal axis of the sheath.

4. The sheath of claim 2 wherein the layer of insulative material comprises a conduit and the sensor strip is disposed on an inside surface of the conduit.

5. The sheath of claim 2 wherein the layer of insulative material comprises an inner conduit portion and the sensor strip is disposed on an outside surface of the inner conduit portion.

6. The sheath of claim 2 wherein the layer of insulative material comprises a conduit extruded from a polymeric material and the sensor strip is coextruded in a wall of the conduit.

7. The sheath of claim 2 wherein the layer of insulative material comprises a conduit made of a flexible polymeric material and the conduit comprises a longitudinal slit providing access for said plurality of electrical conductors through the slit.

8. The sheath of claim 3 wherein the helical pattern comprises a pitch of at least one turn for each sheath length of 20 sheath diameters.

9. The sheath of claim 3 wherein the layer of insulative material comprises an inner wrapped layer of tape and an outer wrapped layer of tape and said at least one sensor strip is disposed between the inner wrapped layer of tape and the outer wrapped layer of tape.

10. The sheath of claim 3 wherein the layer of insulative material comprises an inner wrapped layer of tape, an intermediate wrapped layer of tape, and an outer wrapped layer of tape and a first sensor strip is disposed in a helical pattern between the inner wrapped layer of tape and the intermediate wrapped layer of tape and a second sensor strip is disposed in a helical pattern between the intermediate wrapped layer of tape and the outer wrapped layer of tape.

11. The sheath of claim 5 comprising an insulative coating over the inner conduit portion.

12. The sheath of claim 10 wherein the first sensor strip and the second sensor strip are connected at one end of the sheath.

13. The sheath of claim 10 wherein the first sensor strip and the second sensor strip form a two layer wrap continuous from a first end of the sheath to a second end and back to the first end.

14. A sheath for providing overtemperature and mechanical damage sensing for a plurality of electrical conductors, the sheath comprising:

a layer of insulative material positionable to substantially surround said plurality of electrical conductors; and

at least two sensor strips in communication with the layer of insulative material, each of said at least two sensor strips extending a length of said plurality of electrical conductors, a first of said at least two sensor strips made of a conductive polymer material comprising a positive temperature coefficient of resistivity which increases with temperature, and a second of said at least two sensor strips disposed between an outside surface of the sheath and said plurality of electrical conductors so that mechanical damage originating on an outside surface will result in mechanical damage to said second of said at least two sensor strips before mechanical damage is sustained to said plurality of electrical conductors.

15. The sheath of claim 14 wherein the positive temperature coefficient of resistivity increases at a rate with temperature so as to comprise a switching temperature.

16. The sheath of claim 15 wherein the insulative material is a conduit and said at least two sensor strips are spaced radially about a longitudinal axis of the conduit.

17. The sheath of claim 15 comprising at least four sensor strips disposed in the conduit and spaced radially about a longitudinal axis of the conduit.

18. A preformed harness for providing overtemperature and mechanical damage sensing for a plurality of electrical conductors, the harness comprising:

a molded body comprising a feed end, a main distributor end and an auxiliary distributor end;

a plurality of conductors disposed in the molded body, at least one conductor exiting each of said feed end, main distributor end, and auxiliary end;

at least one sensor strip disposed in the molded body in a mechanical damage sensing pattern between said feed end, said main distributor end, and said auxiliary end whereby mechanical damage occurring from the outside surface of the molded body will open the sensor strip before at least one of said plurality of conductors is damaged, and wherein at least a portion of the sensor strip comprises a material having a temperature coefficient of resistivity which increases with temperature.

19. The harness of claim 18 wherein the positive temperature coefficient of resistivity increases at a rate with temperature so as to comprise a switching temperature.

20. The harness of claim 19 wherein said mechanical damage sensing pattern is a helical pattern with respect to said plurality of electrical conductors.

21. A method for forming a mechanical damage and overtemperature sensing sheath over a plurality of electrical conductors, the method comprising the steps of:

assembling said plurality of electrical conductors in a bundle;

positioning at least one sensor strip in a mechanical damage sensing pattern over the bundle, said at least one sensor strip extending over a first substantial length of the bundle and comprising a positive temperature coefficient of resistivity which increases with temperature, the magnitude of increase in positive coefficient of resistivity sufficient to provide a switching temperature and wherein the mechanical damage sensing pattern over the bundle provides a mechanical damage sensing function by opening said at least one sensor strip upon mechanical damage occurring outside the bundle before said plurality of conductors in the bundle are damaged.

22. The method of claim 21 wherein positioning at least one sensor strip in a mechanical damage sensing pattern over the bundle comprises wrapping said at least one sensor strip in a helical pattern with respect to a longitudinal axis of said plurality of conductors.

23. The method of claim 22 comprising the additional step of wrapping at least one layer of insulative tape around the bundle in a helical pattern and extending a second length of the bundle, the additional step performed before the positioning of said at least one sensor strip.

24. The method of claim 22 comprising the additional step of wrapping at least one layer of insulative tape around said at least one sensor strip in a helical pattern and extending a second length of the bundle, the additional step performed after the positioning of said at least one sensor strip.

25. The method of claim 22 comprising the additional step of wrapping at least one layer of a first insulative tape around the bundle in a helical pattern, the first insulative tape extending a second substantial length of the bundle and before the positioning of said at least one sensor strip and comprising the second additional step of wrapping at least one layer of a second insulative tape around said at least one sensor strip in a helical pattern, the second insulative tape extending a third substantial length of the bundle, and after the positioning of said at least one sensor strip.

26. The method of claim 22 wherein the helical pattern comprises a pitch of at least one turn for each sheath length of 20 sheath diameters.

27. The method of claim 22 wherein the helical pattern comprises a pitch of at least one turn for each sheath length of 10 sheath diameters.

28. The method of claim 22 wherein the helical pattern comprises a pitch of at least one turn for each sheath length of 5 sheath diameters.

29. The method of claim 22 wherein the helical pattern comprises a pitch of at least one turn for each sheath length of 2 sheath diameters.

30. The method of claim 25 wherein the helical pattern comprises a pitch of at least one turn for each sheath length of 20 sheath diameters and the first substantial length is at least 10 percent of the sheath length.

31. A method for forming a mechanical damage and overtemperature sensing sheath over a bundle of insulated electrical conductors, the method comprising the steps of:

disposing at least two sensor strips in a mechanical damage sensing pattern in an insulative conduit, each of said at least two sensor strips extending over a first length of the conduit and at least one of said at least two sensor strips comprising a positive temperature coefficient of resistivity which increases with temperature, the magnitude of increase in positive coefficient of resistivity sufficient to provide a switching temperature; and

inserting a bundle of insulated electrical conductors into the conduit;

whereby the pattern in the insulative conduit provides a mechanical damage sensing function by opening upon mechanical damage occurring outside the bundle before said plurality of conductors in the bundle are damaged.

32. The method of claim 31 wherein the mechanical damage sensing pattern comprises at least four sensor strips spaced radially about a longitudinal centerline of the conduit.