GFCI @ main service

[buck]

Question about requirement for Ground Fault Interrupter at service 1k and 150v to ground. If I have a service rated at 1k(bussing)but install an 800A main breaker(which is adequate for the load), would a GFCI and test still be required?

Thanks in advance

 

[iwire]

Re: GFCI @ main service

First to be clear it is GFP not GFCI, much different trip settings.

As to your question the answer is no, you could actually have a total of six 800 amp breakers as the service disconnect without needing GFP equipment.

 

[pierre]

Re: GFCI @ main service

230.95 Ground-Fault Protection of Equipment. Groundfault protection of equipment shall be provided for solidly grounded wye electrical services of more than 150 volts to ground but not exceeding 600 volts phase-to-phase for each
service disconnect rated 1000 amperes or more.

The rating of the service disconnect shall be considered to be the rating of the largest fuse that can be installed or the highest continuous current trip setting for which the actual overcurrent device installed in a circuit breaker is rated or can be adjusted.


It is not the size of the overcurrent device, it is the size of the DISCONNECT RATING.

A 1000 amp rated disconnect with an 800 amp fuse will require GFP protection and the test as per 250.95.

 

[George Stolz]

Re: GFCI @ main service

What does GFP for equipment accomplish again?

 

[iwire]

Re: GFCI @ main service

Originally posted by georgestolz:
What does GFP for equipment accomplish again?

Hi George, GFP prevents in the words of the handbook a 'burn down' of large services or feeders. With OCPD ratings above 1000 amps the breaker might not ever open when a ground fault happens. The conductor might just keep burning back toward the source kind of like a wick.

A typical GFP setting I see is about 25% of the service or feeder size. A 3000 amp service may have a GFP setting of 600 to 800 amps.

If the all the settings are not correct a simple 277 volt lighting circuit fault to ground can dump an entire building.

We had a super market that kept getting knocked out due to a small short in a chicken roaster and I personally caused a 2000 amp bus duct feeder to shut down when I turned on a 277 volt lighting circuit that had a ground fault. (I trusted the apprentices work. :roll: )

By the way, GFP can be used with fusible switches as well as breakers.

 

[don_resqcapt19]

Re: GFCI @ main service

In the case shown in the first post, no GFP would be required no matter how big the disconnect is, because the voltage it not greater than 150 volts to ground.
Don

 

[buck]

Re: GFCI @ main service

Thanks for the responses guys but I'm still alittle confused from the answers.
The service is 277/480Y and 800A breaker is the MAIN because the service supplies several remote panelboards(more than six which is why the main was installed).
Sounds thru Iwires answer I don't need GF but then thru Pierres I would? Thanks again...

 

[iwire]

Re: GFCI @ main service

As long as it is an 800 amp breaker frame you are all set.

What Pierre's post points out is that if you had a 1000 amp fused switch you would be required to provide GFP protection even if that 1000 amp switch had 800 amp fuses in it.

Or if you had a 1000 amp frame breaker it would need GFP even if you adjusted it down to 800 amps.

 

[buck]

Re: GFCI @ main service

Thanks iwire, I see the reasoning now. One of my concerns was if they decided to up the breaker to 1000A at a later date. But at this point I understand what your saying. Thanks again!

 

[jim dungar]

Re: GFCI @ main service

Bob,

Actually a 1000A frame breaker with an non-adjustable trip of 800A does not require GFP. But a 1000A frame with an adjustable trip unit does.