Shared neutral between normal power and generator power

B

Brownetown

Member
Location
Va
Occupation
Electrican
I have a lighting upgrade of an older high school in process. Fixture for fixture. I came across that in one section of the building they pulled 12/3 one being generator power. One being normal SL power and then a shared neutral between the two. What are your thoughts on that. I know the neutral is obviously the same threw out the 480v/277 service coming in. But tech ally it’s freed from a different source.
 
I don't know if I fully understood the questions, but a shared neutral at the transfer is okay. If these lighting circuits, one regular and another back up, come from different subpanels then they should have their own neutrals. They seem to have pulled it like a multiwire branch circuit which would not be to code if they are fed from different panels/locations. Art. 700.19

You could check Art. 700.17 for more explanation.
 
I’ve never heard “Solid Netural” before. My concern is obviously, someone working on normal power lighting circuit. Turn off normal power and yet there is still a load coming from EM power. I do believe this situation is different than most multi wire branch circuits code. Am I wrong?
 
Brownetown said:
I’ve never heard “Solid Netural” before. My concern is obviously, someone working on normal power lighting circuit. Turn off normal power and yet there is still a load coming from EM power. I do believe this situation is different than most multi wire branch circuits code. Am I wrong?
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Multi wire branch circuits are not permitted for emergency lighting per code. Art. 700.19.

I don't know if that is what you have. I don't fully understand the set up. I would suggest looking at Art. 700.
 
Maybe I didn't understand the question.

What I was thinking is two sources of power generator and utility coming into a transfer switch the neutral from each supply goes on the neutral bar and is not switched. Same thing with a panel with a generator interlock
 
Eddie702 said:
Maybe I didn't understand the question.

What I was thinking is two sources of power generator and utility coming into a transfer switch the neutral from each supply goes on the neutral bar and is not switched. Same thing with a panel with a generator interlock
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Ya. You are right.

But I think the OP is referring to a set of lights fed like 1 hot from a back up panel and another hot from the normal source with a single neutral landed. That neutral would either be landed at the normal source panel or the back up source panel but not at both. Or a MWBC from only the back up panel. Both are not allowed.

It would need to be a 4 wire cable with independent neutrals.

Most of the time, these days, the lights are only feed from a normal source and have a battery pack in them for egress or exit signs.
 
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