Ground Fault Circuit Interrupter with Solid State Relay-Controlled Electromagnetic Contactor and Self-Test End of Life (STEOL) Circuits for High-Current Applications

A ground fault circuit interrupter system for protecting a 240-volt, 60-ampere AC circuit, the system comprising:

• a toroidal sense transformer through which a first line conductor and a second line conductor pass, the sense transformer further comprising a sense winding and a self-test winding wound on the toroidal core, all magnetically coupled, and wherein the system does not comprise a second sense transformer;
• a ground fault detection integrated circuit connected to the sense winding, configured to detect current imbalances indicative of a ground fault;
• a silicon-controlled rectifier (SCR) having its gate connected to an output of the ground fault detection integrated circuit;
• a pair of optically-isolated solid state relays, each having an LED input and a MOSFET output, the LED inputs connected in series in a circuit controlled by the SCR;
• a 240-volt, 60-ampere rated electromagnetic contactor having a coil connected in series with the MOSFET outputs of the pair of solid state relays, and having a first normally-open contact on the first line conductor and a second normally-open contact on the second line conductor;
• a relay synchronized switch circuit configured to maintain energization of the electromagnetic contactor coil and the pair of solid state relays during each self-test event;
• a self-test circuit comprising a periodic stimulus generator and the self-test winding, configured to periodically inject a simulated ground fault signal into the sense transformer at intervals determined by circuit parameters;
• and
• an end-of-life circuit configured to accumulate a monitored quantity responsive to self-test cycle activity, to compare the monitored quantity against a predetermined end-of-life threshold, and to permanently deny power to the load when the monitored quantity exceeds the end-of-life threshold.

A ground fault circuit interrupter (GFCI) for interrupting the flow of current through a pair of lines, wherein one of the pair of lines extends between a first line input and a first line output and the other line extends between a second line input and a second line output, the GFCI comprising:

• A 240-volt, 60-ampere rated electromagnetic contactor having a coil and a first normally-open switch connected between the first line input and the first line output and a second normally-open switch connected between the second line input and the second line output;
• at least one solid state relay (SSR) having an optically-isolated input and a switched output, the switched output connected in series with the electromagnetic contactor coil such that de-energizing the SSR input causes the switched output to open and de-energize the contactor coil;
• a capacitor bus configured to supply operating current to the SSR input, the capacitor bus being charged from a power supply connected across the first and second line inputs;
• a power-on delay circuit configured to inhibit energization of the SSR input until the capacitor bus voltage has risen to a predetermined operating threshold, thereby ensuring controlled turn-on of the electromagnetic contactor upon application of line voltage;
• and
• a fault detection circuit configured to de-energize the SSR input upon detection of a ground fault current imbalance between the lines.