Commercial Kitchen Eq. Trip gfi

[SilverEagle]

I am an electrician with several years experience, and now maintain commercial kitchen equipment in a large hotel. We have remodeled and put in all new equipment. Of coarse, we now have all GFI receptacles. We started experiencing nusiance tripping after the first few months of operation, in all areas of the new kitchens, on several types of eq. from food warmers to convection ovens and refrigeration eq. I have suggested that those circuits that have shared nuetrals should be rewired, and of coarse it was pointed out that this is allowed in the code. However, I have been reading the threads on this subject, and I see that there may be other problems. Nusiance tripping in comm. kit. eq. seems to be common. Does anyone support my idea that shared nuetrals is part of the problem? And what other things might be causing this? Motor starting? Heating elements turning on? I'm thinking inductive reactance in these might cause a problem for a GFI. Most importantly, does anyone have a solution? :-?

 

[ultramegabob]

shared neutrals would be a problem, motors can be a problem, cheap chinese GFCIs can be a problem, as long as the heating element isnt shorting to ground, I dont think that would be an issue....

 

[ultramegabob]

as I understand how a GFCI recept. works, it is basically a small ammeter that is connected to a solinoid and set of contacts. the ammeter is coiled around the power and neutral and as long as their is a equal flow of current in and out of the device it reads zero and the solinoid stays closed, if current is somehow diverted to ground and there is less flowing out on the neutral than what is flowing in on the hot, it triggers the solinoid and opens the contacts inside the device. If you share a neutral between circuits there can be diffent amounts of current on the neutral than what is on the hot side of the GFCI depending when things get turned on and off on those two circuits, causing a nusance tripping situation. I hope this makes some sense....

 

[jerm]

as I understand how a GFCI recept. works, it is basically a small ammeter that is connected to a solinoid and set of contacts. the ammeter is coiled around the power and neutral and as long as their is a equal flow of current in and out of the device it reads zero and the solinoid stays closed, if current is somehow diverted to ground and there is less flowing out on the neutral than what is flowing in on the hot, it triggers the solinoid and opens the contacts inside the device. If you share a neutral between circuits there can be diffent amounts of current on the neutral than what is on the hot side of the GFCI depending when things get turned on and off on those two circuits, causing a nusance tripping situation. I hope this makes some sense....

sharing a neutral on the feeder (line) side of the gfi will have no effect on the gfi's operation. you can't share a neutral on the load side.

if you ruled out cheap chinese gfi's, and your gfi's are tripping, then your current is going to ground someplace, and not all of it is returning on the neutral.

I hope that makes sense. It's getting very late here.

 

[ultramegabob]

sharing a neutral on the feeder (line) side of the gfi will have no effect on the gfi's operation. you can't share a neutral on the load side.

)

http://www.passandseymour.com/knowhowfaq/showquestions.cfm?faqcategory=National+Electrical+Code

read the complete answer to the first question on the Pass and Seymour website...

 

[mdshunk]

If the GFCI is tripping, I would suggest you invest in a megger and meg your equipment hot to ground and see for yourself that it's tripping due to a good reason. Leakage within the appliance. The shared neutral issue, as long as it's on the line side of any GFCI's, is not a problem. There is no such thing as nuisance tripping. There is, however, "reason tripping".

 

[ultramegabob]

some other things to think about....

some other things to think about....

how do they clean this kitchen? do they spray the walls down? open boxes to check for moisture, if so, try installing w.p. in use covers.

is it excessively steamy to where there could be condensation building up inside the recepts? if so, you may need to add exhaust hoods for dishwasher equipment ect.....

 

[ultramegabob]

. The shared neutral issue, as long as it's on the line side of any GFCI's, is not a problem.

I understand that sharing a neutral before the device "shouldnt" be a problem, as all the neutrals are combined together in the panel anyway, but if it doenst make a differnce, why would the manufacture say not to do it?

 

[jerm]

why would the manufacture say not to do it?

Thats the craziest thing I've ever read... Are they suggesting that you take your neutral all the way back to the transformer? I mean, what about the shared neutral at the service?

The gfi has no way of knowing where your line side neutral becomes shared. And it makes no difference. It's not tripping because of that.

 

[augie47]

I think they are simply confirming that you can not share a neutal "downstream" of a GFCI.

 

[jerm]

I think they are simply confirming that you can not share a neutal "downstream" of a GFCI.

But is says on the P&S page "[SIZE=-1]As always, a GFCI can not be installed on a circuit utilizing a shared neutral." They are making a case that your neutral doesn't need to be pigtailed because it won't be on a mwbc. That's just plain wrong. What next, they going to spec a minimum service size? They can't be having any say in what is upstream. slippery slope.
[/SIZE]

 

[Lxnxjxhx]

to further confuse. . .

to further confuse. . .

A toroidal transformer inside the GF device senses the difference between current going out and current returning. If this difference exceeds 4 mA for several seconds it will trip.
If I understand what you're saying, I think shared neutrals will hardly ever have the same current in the neutral as in the hot line.

Look on page 6 of this datasheet
http://www.national.com/ds/LM/LM1851.pdf

 

[electricalperson]

one of these could help proove the appliance has leakage that causes the GFCI to trip

 

[mdshunk]

one of these could help proove the appliance has leakage that causes the GFCI to trip

I have one of those, actually. Works very well for that. The europeans have a similar tool they call a "PAT tester".

 

[iwire]

But is says on the P&S page "[SIZE=-1]As always, a GFCI can not be installed on a circuit utilizing a shared neutral."

I think you are reading it wrong.

If that was the case you could not use it at all. All circuits are supplied by a 'shared' neutral. (The feeders, the services)

I also think it was written by a marketing person, the use of 'shared' in place of common or multi wire branch circuit is a tip off.

 

[mdshunk]

Since they havn't made the Slater tester in probably 20-25 years, the only options we're stuck with are the Simpson 228/229 (which both suck) or the Megger 235303 which is pretty good, but expensive.

Image use by permission of M,M&I

 

[Lxnxjxhx]

Do any GF testers measure AC leakage?

 

[cschmid]

interesting problem..you have some leakage on equipment I do agree..In a commercial kitchen we would of not used shared neutrals and would use GFCI breakers. maintenance is cheaper and the breakers seem to be more reliable than the cheap outlets..it is also safer to reset breaker than outlets, employees will try and reset outlet with wet hands going to panel requires then to dry there hands and environment is better..lucky owner has not removed GFCI outlet to solve their problem..

edited for spelling..

 

[iwire]

On the other hand we always use GFCI receptacles at each point of use.

This is usually per the drawings, one piece of equipment per GFCI.

Mutiliwire branch circuit work fine as well.

 

[480sparky]

...and would use GFCI breakers. maintenance is cheaper and the breakers seem to be more reliable than the cheap outlets....

As well as being far more accessible. Many receps in a commercial kitchen end up buried behind the equipment they serve. Moving some of that stuff can be a real headache, and you don't want to have a GFI trip problem every other day.