GFCI Nusance Tripping?

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biggladant

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Just Installed a temporary service for a construction project and after I left the jobsite I started thinking about what I did. I Installed two Duplex GFCI receptacles in a 2-gang weatherproof box, each on its own circuit but I shared the nuetral. Becuse of this will I have unwanted tripping of the GFCI?
Thanks
 
Re: GFCI Nusance Tripping?

What you did will work perfectlly fine. I did the same thing 3 years ago and my X boss told me what an idiot I was. He drove 40 miles back to the job site to remove the joint I had made with the 2 neutral pigtails from each GFI plug. He said if you plugged a 5 amp drill in 1 plug and a 10 amp saw in another plug then the shared neutral would cause the GFI plugs to trip. He was wrong. I have done it many times without ever having a GFI plug trip.

[ May 14, 2004, 12:18 AM: Message edited by: iaspiretowire ]
 
Re: GFCI Nusance Tripping?

I agree with iaspiretowire. You are fine, and his ex-boss was wrong.

Current leaves the ?hot pin? of one receptacle, enters the 5 amp drill at the hot half of its plug, goes through the drill, returns to the neutral half of the plug, enters the neutral pin of the receptacle, and only then joins with any other current flowing through the shared neutral. Current leaves the ?hot pin? of the other receptacle, enters the 10 amp saw at the hot half of its plug, goes through the saw, returns to the neutral half of the plug, enters the neutral pin of the receptacle, and only then joins with any other current flowing through the shared neutral. Each of the two GFCI receptacles will see only the current flowing out of it and returning to it. So long as each GFCI sees the same current on each of its two legs, neither will trip. The existence of the shared neutral does not enter into the comparison that each GFCI receptacle makes between its hot current and its neutral current.
 
Re: GFCI Nusance Tripping?

I had a problem with this one time, although a little different, I used a 2 pole gfci, with two circuits and one neutral. It tripped all the time and I ended up having to run a second neutral. It happened with a group of receptacles I ran to lab tables at a school. After that I never ran one neutral again. I was under the impression it confused the electronics in some way. Also had a problem with running two gfci receptacles in parallel. Is this different that what you are decribing? thanks.
 
Re: GFCI Nusance Tripping?

If you use two GFI breakers THEN you would have a problem if you used a shared neutral to feed the receptacles supplied by them.

With GFI receptacles any shared neutral is BEFORE the current sensing (which is within the receptacles) and will be of no consequence. You do this all the time to feed kitchen countertop GFI's don't you?

I think you are confusing the two situations.

-Hal
 
Re: GFCI Nusance Tripping?

don't do much residential now, but I think I used to use a shared neutral with a feed through, but not two gfcis with one neutral.
 
Re: GFCI Nusance Tripping?

OP mentions two circuits. Should be on separate phases or will overload single neutral.

[ May 14, 2004, 06:12 PM: Message edited by: awwt ]
 
Re: GFCI Nusance Tripping?

I have shared neutrals on 3 GFI receptacles fed from a 3 phase panel in several restaraunts. Never have heard on nuisance tripping problems, and we still do maintenance and service calls on all theese restaraunts.
With GFI breakers you always have to run separate neutral to panel
 
Re: GFCI Nusance Tripping?

This may be related to the current topic: Can local GFCI reset control be provided with a pair of GFCI outlets to protect the gazebo's 110 outlets AND a 220v lake pump? It's a long hike back to the house to reset the panel circuit breaker when it trips.
 
Re: GFCI Nusance Tripping?

talla,
local GFCI protection is sometimes desirable and, may be possible in your case but you also must be concerned with the protection required of the entire circuit. For example: the branch circuit conductors from the loadcenter all the way out to the gazebo.
I most often deliberate to protect the entire circuit from the loadcenter with a GFCI circuit breaker. If there is any problem with nuisance tripping, then the only thing to do in my opinion is to eliminate all possible causes for nuisance tripping in the system and forget the hassles - forget the walk because it then becomes a non-issue.

I wouldn't replace a light bulb on a gazebo for a customer personally unless the entire circuit was protected. Have ran into it a number of times where the UF cable is run out there like the crow flies and, where buried, is buried less than required by NEC or common sense. Customers have wanted to bring me into a system to do just a little of something with it and that's it. They want it done they're way for what they are willing to pay. Bully me?! Right!
But I am a tradesman and as such am gonna do it the right way from beginning to end.
As a bonus point: nobody wants to find themselves explaining to the fire marshal, police, insurance carrier, AHJ, licensing board, or the customer's family members why they feel only partially responsible - feel only responsible for a part of the circuit they were working on.

[ June 04, 2004, 03:33 PM: Message edited by: grandpapastu ]
 
Re: GFCI Nusance Tripping?

I am a maintenance person at a University and have had the same problem with GFI breakers on two circuits and a shared neutral in prewired raceways. Running a second neutral eliminated that problem.
However, I have a related problem & am getting conflicting information from the contractor and others. Why does a small 2 prong appliance trip the GFI? I think it's because there is a problem in the wiring. The electrical contractor is telling me the GFI senses the potential difference between ground and neutral and a 2 prong appliance will always trip the GFI. Yet I use my 2 prong hair dryer at home on a GFI without problems. Another person is telling me the GFI senses between the hot and the neutral. Just a simple explaination from a uninterested party woul sure help me.
 
Re: GFCI Nusance Tripping?

An electrician is telling you that 2 wire appliances can not run from a GFCI?

Get a new 'electrician' now. :eek:

If a two wire appliance is tripping a GFCI that works fine for other appliances, the appliance has a fault that needs repair.
 
Re: GFCI Nusance Tripping?

Originally posted by ceyer:
Iwire,
That's what I thought & this guy has a masters license.
Click to expand...
cyer, a gfci simply compares current in the ungrounded conductor and grounded conductor. If there is a mis-match, not equal, it energizes the trip coil.
 
Re: GFCI Nusance Tripping?

A gfi receptacle has a sensing ring inside which is like a clamp meter it will open the circuit if I there is a difference between the hot and the neutral of (if I remember correctly)4 to 6 milliamps. First off it does not sense for potential difference which of course is voltage. The purpose of the gfi is for saftey if the hot is given another path to ground the hot and neutral will be unbalanced and the gfi will trip. thats why the test switch is a resistor in series with the neutral. With the receptacle the sensing is inside the device and just protects that one receptacle depending on line or load connection but a breaker senses all the way back in the panel which protects the whole circuit the neutral and hot will vary by two separate hots and one neutral returning to both circuits. Now your appliance could be bad or depending on the appliance if it contains any type of inrush current or basically non-linear it will trip the receptacle. In kitchens your receptacles are gfi protected but not if it is a set appliance or uneasily moved equipment ex: refrigerator because every time the fridge compressor kicked on the inrush would trip the gfi. Its late i typed real quick excuse errors in spelling and full explanation email back for anything not specified sorry its so sloppy and typed so quick
 
Re: GFCI Nusance Tripping?

Jeff,
if the hot is given another path to ground the hot and neutral will be unbalanced and the gfi will trip.
Click to expand...
The GFCI will also trip if the neutral on the load side of the device is given an second path.
thats why the test switch is a resistor in series with the neutral.
Click to expand...
The test load (resistor) is not in series with the neutral. It is connected with one end of the resistor on the neutral on the line side of the current coil and the other end of the resistor connected to the hot wire on the load side of the current coil. This connection causes the unbalanced condition because only the current on the hot wire is seen by the current coil.
Don
 
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