Grounded Conductor Brought to Service Equip.

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ron

Senior Member
4 wire standby generator output and Y utility service is brought to a 3 pole XFER switch per 250.24(C). Does the XFER switch need to specified as 4 wire so there is an official place to terminate the grounded conductors?

Since the gen and utility will have a N-G bond at each source making them separately derived systems, does the ATS need to be 4 pole per 250.20(D) even though there are no 4 wire loads?
 

augie47

Moderator
Staff member
Location
Tennessee
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State Electrical Inspector (Retired)
ron, my though is that as long as you don't switch the neutral, they are NOT SDS's and I know of no requirement for you to switch the neutral.

On rare occasions, I have seen some engineering specifications for switched neutral ATS but am not knowledgeable as to why that was done.
 

ceb58

Senior Member
Location
Raeford, NC
4 wire standby generator output and Y utility service is brought to a 3 pole XFER switch per 250.24(C). Does the XFER switch need to specified as 4 wire so there is an official place to terminate the grounded conductors?

Since the gen and utility will have a N-G bond at each source making them separately derived systems, does the ATS need to be 4 pole per 250.20(D) even though there are no 4 wire loads?

There is no need for a 4 pole switch unless the service is getting over 1000amps with gfi protection. If it is for a lower amp service I would install a 3 pole ATS. They come with an isolated neutral bar in them. Then there is no need for bonding at the gen. Just bring the EGC from the service disco. and the gen. into the ATS and bond them to the can.
 

ron

Senior Member
ceb58,
The issue for me is that there are no 4 wire loads, so I don't need the 4 pole to have accurate GF detection because the neutral load will not go to the wrong place (because there is none).
I'm trying to figure out if there is a code requirement.
 

ceb58

Senior Member
Location
Raeford, NC
ceb58,
The issue for me is that there are no 4 wire loads, so I don't need the 4 pole to have accurate GF detection because the neutral load will not go to the wrong place (because there is none).
I'm trying to figure out if there is a code requirement.

You and me both. Will the ATS carry the full 3000amps? No 277v loads?
 

ceb58

Senior Member
Location
Raeford, NC
ceb58,
The issue for me is that there are no 4 wire loads, so I don't need the 4 pole to have accurate GF detection because the neutral load will not go to the wrong place (because there is none).
I'm trying to figure out if there is a code requirement.

Update. I spoke with one of our State inspectors and he stated that for your set up you would follow 250.30, 250.32 and 250.35A. So it seems that you would bond the neutral in the gen. Then bring your phase conductors,neutral conductor and an EGC to the gen. disco. at the transfer switch. From the gen. disco you can run the 3 phase conductors and an EGC to the transfer switch. This will eliminate the need for a 4 pole switch.
 
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