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GFCI more trouble? #4455
09/28/01 03:40 PM
09/28/01 03:40 PM
glenn35  Offline OP
Joined: Jul 2001
Posts: 40
I have a GFI that hums. Is this normal or could it be defective? It seems to work OK. It trips when I hit the test button and does not have a nuisance tripping problem.

This is a different GFCI than in my previous post.


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Re: GFCI more trouble? #4456
09/28/01 03:44 PM
09/28/01 03:44 PM
Bill Addiss  Offline
Joined: Oct 2000
Posts: 3,905
I've heard Breakers hum, but not GFCI's. Maybe it's on the verge of tripping. I'd try changing it out, it can't mean anything good.


Re: GFCI more trouble? #4457
09/28/01 05:50 PM
09/28/01 05:50 PM
Tom  Offline
Joined: Jan 2001
Posts: 1,044
Shinnston, WV USA
Been awhile since I've taken a GFCI receptacle apart, but there are probably 2 wire coils & possibly a relay that could be making the hum.

GFI receptacles are cheap enough, if you have any doubts about it, replace it.


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Re: GFCI more trouble? #4458
09/28/01 11:27 PM
09/28/01 11:27 PM
johnd24  Offline
Joined: Jul 2001
Posts: 62
could be on with a lighting circuit and getting noise from ballast

Re: GFCI more trouble? #4459
09/29/01 10:06 AM
09/29/01 10:06 AM
Scott35  Offline
Broom Pusher and
Joined: Oct 2000
Posts: 2,720
Anaheim, CA. USA
Sounds to me that you got one with a "Loose" CT [Current Transformer]. The CT is obviously vibrating against it's own mounting means.
Could also be caused from "Noise" on the AC system. That would make a loosely wound or loosely mounted CT hum, along with possibly having humming sounds created by the control circuitry [Diac, trigger, SCR, etc.].

If the sound is faint [barely audible] and the device tests out properly, it's most likely just "Nuisance Noise" - a result of cheap design or sloppy assembly by the manufacturer.

If the sound is loud [easilly audible] and the device has difficulty test tripping, I would suspect the triggering SCR has a few too many charges passing from Cathode through the Gate [semi-shorted SCR].
In that case, remove the GFCI, place it in the Recycle bin, then install a new GFCI [Linked Image]

I have noticed a few GFCI Receptacles which hummed slightly [<5dB], and some that the vibrations can be felt when placing your palm across it. They functioned properly when tested, using various techniques [external loads and/or test button]. These were on Commercial projects with Conduit systems [metallic boxes, conduits, cables and raceways] and Steel Studs, so I figured the sound was more prevailant with all the metal to vibrate through.

As mentioned by others, it wouldn't hurt to replace the device if you do not feel comfortable about the audible humming.

P.S. Is this a GFCI Receptacle, or GFCI Breaker??? If it's a GFCI Breaker, that humming could be the normal contact vibrations of the breaker frame, the trip spring inside the breaker's frame, or the contact points inside the breaker's frame.
Some of these symptoms are normal and not an immediate danger. Some of them can be signs of hidden trouble.
If the humming increases linearally with load, but dissappears with no load, check the mounting and Line [bus] contacting points. Tap the breaker lightly with the back of a screwdriver's handle just in front and behind the handle [on the upward facing surface] to see if the humming varies.
Check the voltage drop across the breaker at various levels of hum. If the VD changes with humming, suspect poor contact seating inside the frame.

BTW: The contact seating pressure situation could be another source of hum in the GFCI Receptacle! Once again, checking the voltage drop across the device [both "Hot" and "Neutral"] with some light tapping can verify this one.
The problem is you need to work with a Live circuit and exposed Receptacle terminals. BE VERY CAREFULL!!!

If you are by any means unfamiliar to working live circuits and techniques to isolate your body from ground / grounded parts of the structure, PLEASE DO NOT ATTEMPT THESE TESTS!!!
Just purchase a new device and replace the noisy one. The $10 - $20 spent is absolutely nothing compared to your life and well being!!!

Scott SET

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Re: GFCI more trouble? #4460
10/02/01 11:09 PM
10/02/01 11:09 PM
Steve Miller  Offline
Joined: Aug 2001
Posts: 329
Bruceton Mills, WV
Trash it, they're a lousy $8.00 and yours is soon to die. Unfortunately it will still pass power but it won't be protected.


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