# GFCI Main Breaker



## uconduit (Jun 6, 2012)

did you mean gfi? gfi and gfci are different.


---
I meant gfp !!


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## MDShunk (Jan 7, 2007)

I think you mean GFP, and yeah, it's normal. I also guess someone set the dials with a guess.


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## Big John (May 23, 2010)

Ground fault protection is really common on large breakers with adjustable trip settings.

And on 277/480V services of 1kA or greater, it's actually a code requirement. 230.95

It's also a really good argument for not doing live-work in office buildings: Seen more than one guy take out the main for a whole building by shorting a 277V lighting circuit because the GFP isn't coordinated properly.


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## MDShunk (Jan 7, 2007)

Big John said:


> Ground fault protection is really common on large breakers with adjustable trip settings.
> 
> And on 277/480V services of 1kA or greater, it's actually a code requirement. 230.95
> 
> It's also a really good argument for not doing live-work in office buildings: Seen more than one guy take out the main for a whole building by shorting a 277V lighting circuit because the GFP isn't coordinated properly.


Yeah, that would be me in at least one instance. Took down part of a reasonably large shopping mall changing out a ballast live in a jewelry store in the 90's. oops. That's the kind of thing you really only need to do once to learn your lesson. At least in my case they seemed to be thankful that there was an electrician onsite when the one main tripped "for apparently no reason". lol. Nobody really needed to know otherwise.


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## Big John (May 23, 2010)

MDShunk said:


> ...At least in my case they seemed to be thankful that there was an electrician onsite when the one main tripped "for apparently no reason"....


 :thumbup: Awesome.

It's one of the reasons I'm real gun-shy about adjusting trip units when online. Turn a screwdriver 1/8" too far and suddenly everything goes dark.


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## MDShunk (Jan 7, 2007)

Big John said:


> :thumbup: Awesome.
> 
> It's one of the reasons I'm real gun-shy about adjusting trip units when online. Turn a screwdriver 1/8" too far and suddenly everything goes dark.


I don't even mess around with them. That's the job for a testing company at commissioning, or taken from the engineer's notes on the prints during the initial install, or from the Square D/Seimens/whoever design specs with the gear package. 

I also bet a lot of jobs get left with the dials the whole way up, such as some guys tend to do during the construction phase.


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## glen1971 (Oct 10, 2012)

Had one client that wouldn't believe me when I said their settings were wrong... Seemed the main would trip when one of the larger roof top units started (new building). Called me and I tried to explain it, but the building manager was an engineer and doubted how that could be.. When the tech from the testing company arrived he looked and they were all set at the minimum setting.. A quick adjustment, and things were running normally..


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## Blayney86 (Jan 18, 2013)

Yeah I know that is what is required but does anyone have any experience in a medical setting with large sterilizers? This building has three 60a 3 phase 240/480 sterilizers that seem to have problems every few months and shut the building down. Has anyone installed ground fault protection on equipment like this before? And in my head as long as I install a GFI that is more sensitive than the main to trip first this should fix the problem correct? I found a 60amp 3 phase GFI that I didn't know existed. Anyone seen or used one of these before??


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## Zog (Apr 15, 2009)

Blayney86 said:


> Yeah I know that is what is required but does anyone have any experience in a medical setting with large sterilizers? This building has three 60a 3 phase 240/480 sterilizers that seem to have problems every few months and shut the building down. Has anyone installed ground fault protection on equipment like this before? And in my head as long as I install a GFI that is more sensitive than the main to trip first this should fix the problem correct? I found a 60amp 3 phase GFI that I didn't know existed. Anyone seen or used one of these before??


You seem confused on the difference between a GFCI(or GFI) and GFP (Ground fault protection).


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## Blayney86 (Jan 18, 2013)

Maybe I am would you mind explaining the difference? I used to believe that the difference was GFI was 5mA and GFP was 30mA but right now I have a GFCI that has selectable settings of 6mA, 10mA and 30mA. As well as the main for the building says GFI on it. So what are the differences you are talking about. The only other thing I've heard is that GFI is people protection and GFP is equipment protection.


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## JRaef (Mar 23, 2009)

Blayney86 said:


> Maybe I am would you mind explaining the difference? I used to believe that the difference was GFI was 5mA and GFP was 30mA but right now I have a GFCI that has selectable settings of 6mA, 10mA and 30mA. As well as the main for the building says GFI on it. So what are the differences you are talking about. The only other thing I've heard is that GFI is people protection and GFP is equipment protection.


Your original understanding would be correct. If you have something calling itself a "GFCI" and it is adjustable above 6mA, it cannot be a Class A GFCI. If it is a GFP, and offers a trip setting below 30mA, that's fine, you can do what you want. But you cannot call that a Class A GFCI. What is it?

By the way, be careful. There are a few IEC vendors selling what THEY call "RCDs" (Residual Current Devices), but some of the bottom feeders try to pass them off as "GFCIs" for use here. You CANNOT use those, they are NOT UL Listed as Class A GFCIs. The trick they pull is to get them UL listed under UL1077 as "Supplemental Protection". You can use them, but ONLY if you have a UL489 listed breaker ahead of them anyway, which means they are redundant.


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## Zog (Apr 15, 2009)

Blayney86 said:


> Maybe I am would you mind explaining the difference? I used to believe that the difference was GFI was 5mA and GFP was 30mA but right now I have a GFCI that has selectable settings of 6mA, 10mA and 30mA. As well as the main for the building says GFI on it. So what are the differences you are talking about. The only other thing I've heard is that GFI is people protection and GFP is equipment protection.


The GFP on the 1000A main breaker you are discussing is for sensing a ground fault high enough to damage equipment, it is either a function on the trip unit or an external relay with a shunt trip on the main breaker. Probally set somewhere around 100-200A. Many different ways this ground current can be measured (Brian John has a nice sticky on this site regarding those methods). 

Chances are pretty good the main breaker in your building is the only breaker in the system with GFP, so any ground fault on equipment can easily trip the main breaker. You need to test the GFP system (Hire a testing company for that) and possibly add GFP to some feeder breakers (Then have it coordinated, hire an engineer for that)


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## brian john (Mar 11, 2007)

A little diddy I wrote some time ago

http://www.electriciantalk.com/f2/addressing-ground-fault-issues-483/


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## brian john (Mar 11, 2007)

Most likely as has been noted the GFP settings are too low.
You could very easily put GFP on the equipment causing the issue, a CT, Current sensor and a shunt trip CB.

Lastly you say 240/480 the system is most likely a 480/277 VAC system.

What voltage are the sterilizers? If they are 208/120 VAC you have bigger issues there is a cross connected neutral between the two systems.
(MOST LIKELY)

There are several things that need to be performed.

1. I would measure for neutral ground current on the main service bond and at all distribution transformers neutral ground bonds.
2. During a scheduled outage lift the neutral ground disconnect link and Megger the downstream neutral to ground.
3. Obtain the proper GFP settings from the electrical engineer (HE WON'T HAVE A CLUE).
4. Adjust the GFP and test PROPERLY.


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## Blayney86 (Jan 18, 2013)

Yes I did mean 277/480 system. These 70-80hr weeks start messing with my head. and the sterilizers are 277/480.


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## erics37 (May 7, 2009)

MDShunk said:


> Yeah, that would be me in at least one instance. Took down part of a reasonably large shopping mall changing out a ballast live in a jewelry store in the 90's. oops. That's the kind of thing you really only need to do once to learn your lesson. At least in my case they seemed to be thankful that there was an electrician onsite when the one main tripped "for apparently no reason". lol. Nobody really needed to know otherwise.


I knocked out half a Walmart doing that once :clap:


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## brian john (Mar 11, 2007)

MDShunk said:


> Yeah, that would be me in at least one instance. Took down part of a reasonably large shopping mall changing out a ballast live in a jewelry store in the 90's. oops. That's the kind of thing you really only need to do once to learn your lesson. At least in my case they seemed to be thankful that there was an electrician onsite when the one main tripped "for apparently no reason". lol. Nobody really needed to know otherwise.


Had an EC do that 5 times in a building during a remodel. Last time he took a trip to the hospital, burnt his hands.

We had previously repaired the GFP and they tried to blame us for the tripping. 

Typically job 6 insurance adjusters, 8 lawyers, property managers, electrical inspector and building engineer all watching us test the GFP. The EC did not show up.


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## Zog (Apr 15, 2009)

brian john said:


> Typically job 6 insurance adjusters, 8 lawyers, property managers, electrical inspector and building engineer all watching us test the GFP. The EC did not show up.


Yep, typical. Someone is always late and you have to wait for them to witness something they have no idea what they are witnessing.


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