N-G bond location

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SMB

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I have two 4-wire generators feeding an ATS with an un-switched neutral. All the neutrals connect to a neutral buss at the bottom of the ATS. From the ATS, I go to an MDP. Can I locate my N-G bond prior to the ATS, inside the ATS or does it have to be downstream since the neutral in unswitched? Is this explained in the NEC somewhere? Thanks for any and all responses.
 

augie47

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Location
Tennessee
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State Electrical Inspector (Retired)
You should already have a neutral-ground/bond in your service equipment. Since your neutral is unswitched by the ATS, that is all you need.
The generator neutrals will still be bonded thru the service bond.
Any other connection would violate 250.24(A)(5)
 

raider1

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Location
Logan, Utah
I agree with Gus.

The gererators in the original post are not seperatly derived and should not have a neutral to ground connection.

Where is the electrical service in relation to the gererators?

Chris
 

SMB

Member
Let me re-phrase. They are not in place yet. Currently there is a shore power source with the N-G bond in a disconnect external to the ATS shelter (this is a portable shelter). It is going to be shipped and then the two generators are going to be added as sources of power. The genests neutrals will be brought to the ATS. I was going to put the N-G bond outside in an external connection box before the ATS where the genset cables will land (large terminal strip). However, I'm being told since the ATS is unswitched, this is not correct and must be after the ATS. I believe it has something to do with circulating currents going back to the non-operating genset on the neutral if unswitched since they will be all connected together.

Thanks

Let me add the shore power will go away so the original N-G bond will also go away.[/B]
 
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raider1

Senior Member
Staff member
Location
Logan, Utah
Is the ATS listed for use as service equipment?

You will need to have a service disconnecting means installed at the structure, this is where your main bonding jumper must be located.

Chris
 

SMB

Member
Yes it is and there is an MDP in a panel next to the ATS with a 400A MCB. I can put the bond in the ATS enclosure since it is service rated and the MCB is readily accesible.
 

raider1

Senior Member
Staff member
Location
Logan, Utah
I can put the bond in the ATS enclosure since it is service rated and the MCB is readily accesible.

Yes, if the ATS is listed for use as a service disconnecting means and the overcurrent device for the service is located immediately adjacent to the ATS.

Chris
 

RUWired

Senior Member
Location
Pa.
It would be my opinion that either of the two gen sets would be the stand alone power plant making either of the two a SDS and thereby requiring the system bonding jumper to be made at the source or the first disconnect or ocpd. That would in all likeliness put the jumper in either of the two gen sets if equiped with a disconnect or breaker. After establishing the main power plant, the second gen set would be a non sds when using a solid neutral switch.

Rick
 
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