GFCI with enhanced surge suppression

• US 7,012,500 B2
• Filed: 03/19/2004
• Issued: 03/14/2006
• Est. Priority Date: 03/19/2004
• Status: Expired due to Fees

• Current Assignee: Leviton Manufacturing Company Incorporated
• Original Assignee: Leviton Manufacturing Company Incorporated
• Inventors: Chan, David Y., Bradley, Roger M., Power, John J.
• Primary Examiner(s): Easthom, Karl D.
• Application Number:
  US10/804,510
• Publication Number:
  US 20050206493A1
• Time in Patent Office: 725 Days
• Field of Search: 338/20, 338/21, 362/125, 362/127
• US Class Current: 338/20
• CPC Class Codes: H01C 7/126 Means for protecting against excessive pressure or for disconnecting in case of failure

Abstract

An MOV element is physically and electrically connected to a heat sensitive material which changes from a low impedance path to a high impedance path, such as a spark gap, when the temperature of the MOV element rises to a temperature below that at which the MOV will enter into its thermal runaway state. More specifically, the heat sensitive material is located on a surface of the MOV and is electrically connected in series with the MOV. In operation, as the MOV gets hot, it heats the heat sensitive material. As the heat sensitive material gets hot, it starts to separate from the surface of the MOV to form a spark gap which is electrically connected in series with the MOV element to help dissipate excessive voltage. The heat sensitive material on the surface of the MOV element can be a coating of epoxy which cracks and/or breaks away, at least partially from the surface of the MOV element during the occurrence of a high voltage transient surge, or it can be a solder that sputters to form an arc path during the occurrence of a high voltage transient surge. In operation, when a GFCI is subjected to a high voltage transient surge above a certain magnitude, the heat sensitive material forms a spark gap which is in series with the MOV and prevents the GFCI from going into its destructive thermal runaway condition. Thus, prior to the MOV entering its thermal runaway state, it goes from being only an MOV to an MOV in series with a spark gap which can be used to protect an up stream GFCI during the occurrence of a high voltage transient surge.

Claims

1. A protection device comprising:

a ground fault circuit interrupter (GFCI) having phase and neutral line side conductors for connection to a source of current and a load side for connection to a load, wherein said GFCI includes a circuit interrupting portion to automatically break a conductive path between said line side and load side upon detection of a ground fault, a reset portion to break and reset said conductive path, and a reset lockout portion to prevent said GFCI from being reset if said circuit interrupting portion is non-operational; and

a surge protection device coupled across said phase and neutral line side conductors of said GFCI, said surge protection device comprising;

a metal oxide varistor (MOV) which increases in temperature when subjected to a voltage spike;

a thermal fusible layer coupled to a surface of said MOV, said thermal fusible layer capable of conducting current and adapted to form a high impedance path by separating, at least partially, or cracking, or sputtering, or melting, from the surface of the MOV when the temperature of the MOV exceeds a predetermined temperature to form of a spark gap electrically connected in series with the MOV to help dissipate voltage surges;

a first conductor having a first end and a second end, said first end coupled directly to a first surface of said MOV and said second end coupled to one of said line side conductors of said GFCI; and

a second conductor having a third end and a fourth end, said third end coupled directly to said thermal fusible layer and said fourth end coupled to the other of said line side conductors of said GFCI wherein said first conductor, said thermal fusible layer and said MOV establish a spark gap there between when said thermal fusible layer forms a high impedance path due to heat provided by said MOV as it exceeds said predetermined temperature.

2. The protection device of claim 1 wherein said MOV has a first face and a parallel, spaced apart second face and said thermal fusible layer covers less than the full extent of said first face.

3. The protection device of claim 2 further comprising:

a layer of insulation on said thermal fusible layer; and

a connection tail extending from said thermal fusible layer onto said layer of insulation and said second conductor third end is coupled to said thermal fusible layer through said connection tail.

4. The protection device of claim 3 wherein said thermal fusible layer and said layer of insulation are generally concentric and circular.

5. The protection device of claim 1 wherein said thermal fusible layer is rectangular and covers less than the full extent of said surface of said MOV.

6. The protection device of claim 5 further comprising:

a rectangular layer of insulation upon said rectangular thermal fusible layer; and

a connection tail extending from said thermal fusible layer onto said layer of insulation and said second conductor third end is coupled to said thermal fusible layer through said connection tail.

7. The protection device of claim 1 wherein said MOV has a first face and a parallel, spaced apart second face and said thermal fusible layer is of a cruciform shape mounted adjacent said first face.

8. A protection device for a metal oxide varistor (MOV) which can protect a ground fault circuit interrupter (GFCI) comprising:

a GFCI having phase and neutral line side conductors for connection to a source of current and a load side for connection to a load, wherein said GFCI includes a circuit interrupting portion to automatically break a conductive path between said line side and load side upon detection of a ground fault, a reset portion to break and reset said conductive path, and a reset lockout portion to prevent said GFCI from being reset if said circuit interrupting portion is non-operational; and

a surge protection device coupled across said phase and neutral line side conductors of said GFCI, said surge protection device comprising;

a first semi-circular segment MOV defined by a first straight side edge and a first curved side edge;

a second semi-circular segment MOV defined by a second straight side edge and a second curved side edge;

said first semi-circular segment and said second semi-circular segment generally describing a circular MOV when said first straight side edge is held parallel with said second straight side edge;

said first semi-circular segment MOV and said second semi-circular segment MOV heat up when exposed to voltage spikes;

said first semi-circular segment having a first front surface and a first rear surface, said second semi-circular segment having a second front surface and a second rear surface;

a thermal fusible layer extending between said first semi-circular segment first straight edge surface and said second semi-circular segment second straight edge surface, said thermal fusible layer capable of conducting current there through and adapted to form a high impedance path by separating, at least partially, or cracking, or sputtering, or melting, from the first and second MOV segments when the temperature of the MOV exceeds a predetermined temperature to form a spark gap electrically connected in series with the MOV to help dissipate voltage surges;

a first conductor having a first end and a second end, said first end coupled to one of said first front or first rear surfaces of said first semi-circular segment and said second end coupled to one of said line side conductors of said GFCI; and

a second conductor having a third end and a fourth end, said third end coupled to one of said second front or second rear surfaces of said second semi-circular segments and said fourth end coupled to the other of said line side conductors of said GFCI whereby current is permitted to flow through said first straight edge surface of said first semi-circular segment and said second straight edge surface of said second semi-circular segment establish a spark gap there between when said thermal fusible layer forms a high impedance path due to the heat provided by said first and second MOV segments as it exceeds said predetermined temperature.

9. The protection device of claim 8 further comprising;

a layer of insulation surrounding said first front surface, said first curved side surface, said first rear surface, a rear surface of said thermal fusible layer, said second rear surface, said second curved side surface, said second front surface and a front surface of said thermal fusible layer.

10. The protection device of claim 9 wherein said layer of insulation has a top surface and a bottom surface.

11. The protection device of claim 9 further comprising:

an air gap extending from said layer of insulation top surface to said bottom surface along one side of said thermal fusible layer.