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Ground fault pickup test for 120V GFCI circuit breaker (How-to)

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    Ground fault pickup test for 120V GFCI circuit breaker (How-to)

    You can verify the pickup value of small GFCI circuit breakers using a control power source and a separate low current source. The test procedure is not much different than testing a switchboard ground fault relay with zero sequence CT, its just on a much smaller scale.

    In this example, we are using a single-pole, 120V, 20A GFCI circuit breaker with 5mA sensitivity.

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    Step 1: Apply 120V source across breaker to energize GFCI coil. Put your hot lead on the line side terminal of the circuit breaker, and your neutral lead on the curly tail. Verify that the relay has control power by using the push to test button, the circuit breaker should trip when the button is pushed.

    Step 2: Using a trip unit secondary test set (or relay set) and multimeter in series, connect a low-level current source from the neutral return to the curly tail on the circuit breaker. Its possible to safely push a separate current source despite having 120V control power on the breaker because there is no potential on the neutral terminals. Verify the absence of voltage on these terminals before connecting to them!

    Step 3: Slowly raise current on the test set and the breaker should trip at approximately 5mA. If you are having trouble finding the trip value you can use the MAX record function on your meter to hold the number.

    That’s all there is to it. I used an Amptector test set because there were no relay sets available. The Amptector was nice because you can easily clip jumpers onto the output terminals, but just about any secondary test set that you can tap onto should work.

    The procedure outlined above only tests the pickup value. You could always rig up some contacts and a timer or use a relay test set for a timing test but that would be overkill in my opinion (it should trip instantaneously).

    I couldn’t figure out a way to do a no trip because of the control power across the main contacts. In order to do a no trip you would need to series the test current through the breaker contacts and neutral sensor.

    I'm not exactly sure why the customer wanted to test these breakers. This was a first for our company and I was the one lucky enough to get the task. I had never tested these before, so it took a few attempts to get things working.

    Any feedback on this is appreciated. It was a fun experiment and I just wanted to share my findings with the community in hopes that it will help someone in the future with a similar situation.


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