Definition of Dual-Fed Service

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JesseETG

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I'm studying up on the code book and after reading 250.24 (A) (3) I'm confused of what exactly is considered a dual-fed service. Does anyone know the true definition of a dual-fed service ?
 
I am not certain but what about a generator feed as well as a utility feed. Or perhaps a solar and utility feed.
 
Generators and solar feeds would not be services though.

It does mention secondary ties, which would be covered by 450.6

However I don't believe anything there is service related, so not sure why the word service is included in what is mentioned in 250.24(A)(3). Any such tie on service sources wouldn't really be under the scope of NEC anyway, so maybe should have been worded differently? Service is a word in NEC that pretty much means supplied by the utility in some way or another.

I could see "double ended service" being something that maybe is applied more so with 1000 volts and higher services?

Need to do some digging to figure this out, especially on the higher voltages as I am not very familiar with what might be common with those.
 
A dual-fed service is two services that are interconnected with a tie-breaker.

240.24(A)(3) says that that instead of needing a separate grounding electrode conductor connected to the grounded conductor at each of the two services, a single grounding electrode conductor connection can be made to the grounded conductors of each service at the tie point.
 
david luchini said:
A dual-fed service is two services that are interconnected with a tie-breaker.

240.24(A)(3) says that that instead of needing a separate grounding electrode conductor connected to the grounded conductor at each of the two services, a single grounding electrode conductor connection can be made to the grounded conductors of each service at the tie point.
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I kind of thought it probably was two interconnected "services". Yet about only information on tie circuits I could come up with was in 450.6, and am sort of presuming that would need to be something on customer side of service point to apply and anything on utility side would be outside scope of NEC, or that there would be some details in art 230 if you could have both the utility feeds to some "service gear' and ties between them.
 
kwired said:
or that there would be some details in art 230 if you could have both the utility feeds to some "service gear' and ties between them.
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I'm not sure what art 230 would say. Each service already has to meet the requirements of Art 230 independently. The decision to tie the two services together is more of a design issue.
 
david luchini said:
I'm not sure what art 230 would say. Each service already has to meet the requirements of Art 230 independently. The decision to tie the two services together is more of a design issue.
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Yet is not really the same thing as secondary ties on non service transformers. Tie them together ahead of the service point and from art 230 perspective you have nothing different than if you had parallel conductors from a single source.

Only other thing I can maybe see is the two sources aren't so much for increased capacity but for more reliability/continuity of service, but that don't make much sense if both fed from same primary conductors either so there must be two primary circuits of some sort involved to be worth any such effort I would think. Maybe places you might see it is critical operations that can't be shut down unless done in an orderly fashion, emergency call/response centers, etc. and even those likely still have on site standby source as well.
 
kwired said:
Yet is not really the same thing as secondary ties on non service transformers.
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You've lost me...250.24(A)(3) doesn't say anything about non service transformers...or transformers at all.

kwired said:
Tie them together ahead of the service point and from art 230 perspective you have nothing different than if you had parallel conductors from a single source.
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They're not tied together ahead of the service point. They're tied together after the service point.
 
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