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Discussion Starter · #1 ·
I've run into something new and maybe one of you gents smarter than me can help me understand.

I'm currently running a job that we are installing a generator and two ATS's in. One is a 3 pole with no neutral going to a UPS. The other is a 3 pole with solid neutral. I've done this before and you just can't install a system bonding jumper at the generator.

Here's the issue my inspector is bringing up. Apparently in the same building another tenet has just renovated and they've installed a generator that is 4 pole switched neutral, thus making system bonding necessary. I'm being told we cannot install a 3 pole w/solid neutral because they've installed a 4 pole switch and bonded their neutral.

I'm not understanding what the negative effect is on our, or their generator? Is there a relevant code section that addresses this?

Appreciate your time.
 

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Does each tenant have a service or is there one service and each tenant fed with a four wire sub? You said the UPS is fed with 3 phase, that must be a second service.
 

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Discussion Starter · #3 · (Edited)
Does each tenant have a service or is there one service and each tenant fed with a four wire sub? You said the UPS is fed with 3 phase, that must be a second service.
Other tenant installed their own service.

We have two loads on our generator, one that goes to a UPS 3-phase no neutral and another feed for a standby distribution 3-phase with neutral. UPS has a transformer so we'll be installing a system bonding jumper there.

Sorry for the confusion, I see where I worded it poorly.

His issue is that their generator ATS is switching the neutral, and ours is not. Theirs will have a system bonding jumper, ours will not. In his words, " Neither is wrong, but you can't do both. "
 

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Hackenschmidt
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His issue is that their generator ATS is switching the neutral, and ours is not. Theirs will have a system bonding jumper, ours will not. In his words, " Neither is wrong, but you can't do both. "
From your telling the inspector has an idea in his head but not an actual code citation.

If the ATS switches the neutral, you must bond EGC to neutral in two places, the usual one on utility power, one at the generator for when on generator power. If you don't bond at the generator, your EGC won't be bonded on generator power. If the ATS does not switch the neutral, you must NOT have a main bonding jumper EGC to neutral at the generator, because the main bond at the service is always there, and if you bond at the generator, the neutral and EGC are parallel paths for neutral current, and you'll have unwanted neutral current on the EGC between the generator and the utility main bonding jumper.

I am thinking since the other tenant has their own service and their own main bonding jumper, what happens at or downstream from your service disconnects doesn't affect each other - so you don't have to coordinate your ATS with your neighbors.

Is the UPS an SDS?
 

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Discussion Starter · #5 ·
From your telling the inspector has an idea in his head but not an actual code citation.

If the ATS switches the neutral, you must bond EGC to neutral in two places, the usual one on utility power, one at the generator for when on generator power. If you don't bond at the generator, your EGC won't be bonded on generator power. If the ATS does not switch the neutral, you must NOT have a main bonding jumper EGC to neutral at the generator, because the main bond at the service is always there, and if you bond at the generator, the neutral and EGC are parallel paths for neutral current, and you'll have unwanted neutral current on the EGC between the generator and the utility main bonding jumper.

I am thinking since the other tenant has their own service and their own main bonding jumper, what happens at or downstream from your service disconnects doesn't affect each other - so you don't have to coordinate your ATS with your neighbors.

Is the UPS an SDS?

UPS is an SDS, correct. I will be bonding at the UPS.

Everything you're saying is as I'm installing it, it's my understanding of code and correct installation. Yet, he plans on coming by on Tuesday and failing my ATS which has a neutral and doesnt switch it, because the other tenet's ATS switches their neutral.

I explained I wasn't going to bond my generator, he pointed out that the other tenet bonding their generator is going to be an issue for me. He was in a hurry and had to leave, but said we'd talk more about it when he came in again.

I am thinking since the other tenant has their own service and their own main bonding jumper, what happens at or downstream from your service disconnects doesn't affect each other - so you don't have to coordinate your ATS with your neighbors.
Yup, that's pretty much where I was at. I was at a loss of words when he said he'd fail my ATS when he came back. I guess I'll need to hear his argument and see if I can persuade him differently.
 
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