Nec 700.5(b)

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erickench

erickench

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Brooklyn, NY
I am preparing a power point presentation for licensed P.E.'s in New York for their continuing education requirements and I just need a little clarification. The last sentence in the above NEC section state's:

A portable or temporary alternate source shall be available whenever the emergency generator is out of service for major maintenance or repair.

Let's assume you have a system that is fed from a utility with an ATS that transfers over to an emergency generator upon sensing loss of power. This alternate source that the NEC 700.5(B) speaks of is it a third power source that's used to replace the emergency generator temporarily?
 
Has anyone ever seen such a case? I could understand if the emergency generator which itself is a back-up is taken off line for repairs. They would bring in a portable generator in case the ATS transfers over due to power loss at the utility service. I'm just wondering if this is the correct interpretation of the NEC and are such procedures common practice in the industry.
 
You bet, I cannot disable an emergency source in an occupied building unless I have another source.

This often means placing a temp unit outside and running temp cables into the ATS along with a the two wire start circuit.

I can't help but mention this temp setup cannot be done with many Generac ATSs as the brains for the ATS are actually located in the Genrac generator itself and it does not provide a simple two wire start circuit that the portable unit will need.
 
A portable or temporary alternate source shall be available whenever the emergency generator is out of service for major maintenance or repair.
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What is major maintenance?

I don't know, I would say shutting the unit down for simple fluid changes and normal maintenance would not require (and I have never seen it done) another available source.

Pulling an intake off to replace gaskets seems like we would wise to have another source available.

Replacing a crank shaft, no doubt in my mind you better have another source available.

In my humble opinion we should take into account how quickly the machine could be fired back up during a power failure while the technician is still on site.

Think of the issues of a pitch black occupied building, exit signs and egress lighting all out. Not a good situation, someone will get "hurt" and find a lawyer.
 
This is where you need to look at 708.


I can't help but mention this temp setup cannot be done with many Generac ATSs as the brains for the ATS are actually located in the Genrac generator itself and it does not provide a simple two wire start circuit that the portable unit will need
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I agree with Bob if it is a Generac set up and it has the HTS ATS it is a "dumb switch" with all the brains in the gen. controller. If it is an RTS or GTS ATS then the brains are in the switch. Ether way you could still have a portable unit on site and still run the load by physically wireing in the stand by and operating it manually.
 
ceb58 said:
Ether way you could still have a portable unit on site and still run the load by physically wireing in the stand by and operating it manually.
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Sure, but in most cases it is not economical to have guy standing by 24/7 waiting to flip a switch. :grin:
 
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