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by **RunsWithCrouse-Hinds** on Thu May 09, 2013 3:04 pm

Do GFCI outlets always have issues with the line filters in cabinets? I recently tried to turn on a 20+ year old NEMA TS1 cabinet the other day on a GFCI circuit, and every time I turned on the main cabinet power the outlet would trip (not the breaker). I'm pretty confident it's because of the line filter, but I just wanted to ask here before I went to the trouble of bypassing it. It's also got lighting arrestors and other stuff of course so I wanted to see what my main culprit might be.

Thanks for your thoughts!

by **Mike80** on Thu May 09, 2013 3:28 pm

It is probably due to the line filter. Line filters usually have capacitors tied between each line and ground (metal case of the line filter). Small amounts of current will flow through the capacitors due to the 60 Hz power frequency and the frequencies of any other noise being generated. The GFCI outlet compares the current flowing from the hot side and back to the neutral side. If it sees a current imbalance above a threshold, it will trip because the current is flowing elsewhere. This is how GFCI outlets protect people in wet locations because if the current isn't going back to the outlet, it is probably going through you directly to ground.

by **notMUTCDcompliant** on Thu May 09, 2013 5:52 pm

Agree, line filter

by **TacomaJoe** on Thu May 09, 2013 9:07 pm

It's the line filter, same thing with Easy's cabinet. The capacitor in the line filter passes enough current to make the GFCI think that you are being electrocuted so it tries to save your life.

The solution is to isolate the filter from the cabinet so that the metal shell of the filter isn't in contact with the metal of the cabinet (connect filter case terminal to neutral). This was the first generation filter. The newer ones have an isolated post that goes to neutral presenting no issues to the GFCI.

The test is to wire the cabinet with just the hot and neutral connected, then measure the voltage between the hot and the cabinet. Should be zero.

by **Macsignals** on Fri May 10, 2013 6:20 am

Yep it's the line filter, and/or the neutral being bonded to the cabinet itself somewhere. Like Mike and Joe explained, if even a small amount (it used to 6 milliamps I believe it's 3 now) of current flows back on the ground(ing) wire, the GFCI will trip due to the imbalance. On my NYC Eagle cabinet it was both, the line filter and the neutral bus was bonded to the cabinet.

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