Automatic Transfer Switch

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woodduder

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West Central FL.
I am wiring a building with a 277/480v 3PH 4W service with a 1200 amp GFI main disconnect. It also has an emergency generator to supply lighting for life safety purposes. Is there any reason I would be required to provide a 4 pole transfer switch, creating a separately derived system or would a 3 pole be OK? I can not find anything in NEC that would require a separately derived system.
 
Re: Automatic Transfer Switch

Originally posted by woodduder:
I am wiring a building with a 277/480v 3PH 4W service with a 1200 amp GFI main disconnect. It also has an emergency generator to supply lighting for life safety purposes. Is there any reason I would be required to provide a 4 pole transfer switch, creating a separately derived system or would a 3 pole be OK? I can not find anything in NEC that would require a separately derived system.
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Contact the Engineer who designed the system.
 
Re: Automatic Transfer Switch

It is a matter of choice. But the choice should be made on technical merits, not merely on costs. If the plans presently call for 4-way switching, you don't get to "value engineer" it to a 3-way, just to save money. There are reasons that are more important than costs.
 
Re: Automatic Transfer Switch

I am wiring a building with a 277/480v 3PH 4W service with a 1200 amp GFI main disconnect
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In most cases this fact (GFP) will require the use of a 4 pole transfer switch.
Don
 
Re: Automatic Transfer Switch

I want to provide a little more info on this question. The engineer did not supply any specs on the transfer switches or generator itself nor did he specify on the riser drawing 3 pole or 4 pole transfer switches, therefore my generator supplier simply provided the most cost effective item to the customer. We submitted the 3 pole transfer switch and he turned it down even though there is nothing on the plans or specs to indicate 4 pole.
 
Re: Automatic Transfer Switch

If you have ground fault protection, then the a 3 pole or solidly grounded neutral will effect the ground fault sensing. The IEEE orange book has diagrams to show how this works.
 
Re: Automatic Transfer Switch

No specs?
That sounds as bogus as "provide smoke detection per NFPA 72", "Provide sprinkler protection per NFPA 13" and "Provide lightning protection per NFPA 780".
Sounds like a big change order is coming your way, due to poor contract documents.
 
Re: Automatic Transfer Switch

Hey Ron, What exactly did you mean about the "bogus" statement? I always run into having the burden of designing electrical(or parts of) systems because there has been NO engineering of the electrical system, and would like some good arguments to give the Contractor/Owner.
Thanks
 
Re: Automatic Transfer Switch

It's "bogus" in the sense that it is an attempt (by the owner or by the engineer acting on the owner's behalf) to lay the burden on the contractor, without having to do any actual work of their own. But I don't see it as an opportunity for a change order. If you leave something out, and if the cited reference says that it belongs in, then you won't get paid to add it back in.
 
Re: Automatic Transfer Switch

Dave, it stands for "Ground Fault Protection", (of equipment) see article 100 definition and then read 230.95

Roger

[ January 18, 2006, 04:25 PM: Message edited by: roger ]
 
Re: Automatic Transfer Switch

Originally posted by davedottcom:
What does GFP stand for and why are they used on commercial Mains?
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Ground fault protection and it is sometimes required.

230.95 Ground-Fault Protection of Equipment.
Ground-fault 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.
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215.10 Ground-Fault Protection of Equipment.
Each feeder disconnect rated 1000 amperes or more and installed on solidly grounded wye electrical systems of more than 150 volts to ground, but not exceeding 600 volts phase-to-phase, shall be provided with ground-fault protection of equipment in accordance with the provisions of 230.95.
Exception No. 1: The provisions of this section shall not apply to a disconnecting means for a continuous industrial process where a nonorderly shutdown will introduce additional or increased hazards.
Exception No. 2: The provisions of this section shall not apply to fire pumps.
Exception No. 3: The provisions of this section shall not apply if ground-fault protection of equipment is provided on the supply side of the feeder.
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At these voltage and current levels the breaker may never open during a ground fault, the metal involved in the ground fault might just keep 'blowing out of the way'.
 
Re: Automatic Transfer Switch

Originally posted by iwire:
At these voltage and current levels the breaker may never open during a ground fault, the metal involved in the ground fault might just keep 'blowing out of the way'.
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But why is this issue unique to a wye system? Why would a delta system not require GFP?
 
Re: Automatic Transfer Switch

Originally posted by peter d:
But why is this issue unique to a wye system? Why would a delta system not require GFP?
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Pete that is a good question and I wish I had a good answer.

I suspect the answer is the same reason why we can not protect the secondary side of a Wye transformer with the primary OCP.
 
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