Bonding/Generator

[alixenos]

Hi,

I've been working on a project that requires an emergency generator and my senior PM added a note that says " Generator is not considered a separately derived system and is to be grounded through the building electrode system. Do not bond generator neutral to generator frame"

Can anyone explains what he meant by this and where in the NEC this note fall to?

Thank you.

 

[ron]

It means that you will not be switching the neutral in the transfer switch along with no N-G bond at the generator. NEC 250.30

If it is a larger generator 480V and 1000A or more, you will need to deal with ground fault detection, and would want to reconsider if it is separately derived or not.

 

[Joe.B]

Article 100 - Definitions
Separately Derived System. An electrical source, other than a service, having no direct connection(s) to circuit conductors of any other electrical source other than those established by grounding and bonding connections. (CMP-5)

 

[Choice_Gorilla]

If it is a larger generator 480V and 1000A or more, you will need to deal with ground fault detection, and would want to reconsider if it is separately derived or not.

Not to high jack the thread, but can you expand on this a little if you don’t mind. I have I large generator job coming up.

 

[infinity]

I've been working on a project that requires an emergency generator and my senior PM added a note that says " Generator is not considered a separately derived system and is to be grounded through the building electrode system. Do not bond generator neutral to generator frame"

Also take a look at 250.35(B).

 

[ron]

Not to high jack the thread, but can you expand on this a little if you don’t mind. I have I large generator job coming up.

The code requires ground fault detection if it is an Article 700 or 701 generator and ground fault protection if it is an Article 702 generator, if it is 480V and 1000A or more per code. For accurate detection / trip, you don't want the neutral current willy/nilly returning to its source via any available path, you would want to switch the neutral at the transfer switch and bond the N-G at the generator.

Google 3 pole or 4 pole transfer switches. Here is an example https://resources.kohler.com/power/kohler/industrial/pdf/3_Pole_ATS_White_Paper.pdf

 

[qcroanoke]

Not to high jack the thread, but can you expand on this a little if you don’t mind. I have I large generator job coming up.

I understand that if utility and standby both have ground fault protection you will need to switch the neutrals in the ATS thus creating a separately derived system.