No Neutral at Generator - 480/277 system w/ 1-phase loads?

S

Sjohns4

Member
Location
Huntington WV
Occupation
Engineer
I’m looking at an existing installation. We have a 480v Wye service to the building. Basically the HVAC and sewer pump are 480/3, then we have a 120/208 transformer for outlets, and two separate 480V sub panels full of 1-pole light circuits. There as a 3-pole manual transfer switch with generator conductors ran from an enclosure with lugs for a generator connection. However I’m just seeing 3 phase conductors and the EGC lugs.

Seems to me we’re missing the neutral??

Pretty sure there has never been a generator hooked up.

Is there a scenario where only hooking up 3 phase conductors and the EGC to the generator will allow the lights & transformer (if it’s Wye primary) to work correctly?

Thanks,

Mike
 
Thanks. Wanted a sanity check before I raised the issue in case the original installer knew something I didn’t.

Just for curiosity sake though: what would happen to the voltage on the secondary side of the transformer? Would it be out of whack corresponding to the load on each phase?
 
augie47 said:
Don, if there is no neutral load despite the service being wye, would the generator not be sufficient without a neutral ??
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There are 480 volt line to neutral loads.
"and two separate 480V sub panels full of 1-pole light circuits."
I am not aware of any way to supply 480 volt lighting loads from single pole breakers without a neutral.
 
Sjohns4 said:
Is there a scenario where only hooking up 3 phase conductors and the EGC to the generator will allow the lights & transformer (if it’s Wye primary) to work correctly?
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Even in the rare case of the transformer the supplies the 208Y/120 volt system having a wye primary, it is not a common practice to connect the neutral on the primary.
 
Sjohns4 said:
Is there a scenario where only hooking up 3 phase conductors and the EGC to the generator will allow the lights & transformer (if it’s Wye primary) to work correctly?

Thanks,

Mike
Click to expand...

Are you sure you have 3 hots and the EGC, and not 3 hots plus a grounded conductor serving as both neutral and fault current path?

I'm not up on the current code requirements for generators, so this might not be legal, but if the generator is connected like a service then it would be capable of supporting 277V L-N loads.
 
don_resqcapt19 said:
One pole breakers are only used for line to neutral loads except in the case of a corner grounded system, and there is nothing to suggest that the service is a corner grounded system.

"and two separate 480V sub panels full of 1-pole light circuits."
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And voltage for for line/N single poles loads off a 480/277 wye is what?
 
fastline said:
And voltage for for line/N single poles loads off a 480/277 wye is what?
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It is 277 requiring a neutral from the generator to supply those loads. The issue is that the OP says the generator is intended to supply those 277 volt loads, but there is no neutral from the generator to the transfer switch.
 
winnie said:
Are you sure you have 3 hots and the EGC, and not 3 hots plus a grounded conductor serving as both neutral and fault current path?

I'm not up on the current code requirements for generators, so this might not be legal, but if the generator is connected like a service then it would be capable of supporting 277V L-N loads.
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I think that you would still need an EGC between the generator and the transfer switch.
However if it is connected like a service, it would work. Just can't think of a way to make code compliant.
 
don_resqcapt19 said:
It is 277 requiring a neutral from the generator to supply those loads. The issue is that the OP says the generator is intended to supply those 277 volt loads, but there is no neutral from the generator to the transfer switch.
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I was just making that point. Any of those 1 pole loads prove 277V connections, thus neutral, thus a neutral from the generator is required. As you said. But you said 480V, which gets people confused.
 
But if the generator is feeding to primary side of the transformer, no neutral would be needed, correct?

The neutral would be derived on the secondary side of the xfmr.

And I assumed the “480 panels” are 3 phase panels with 277v lighting loads, which require a neutral.
 
Seven-Delta-FortyOne said:
But if the generator is feeding to primary side of the transformer, no neutral would be needed, correct?

The neutral would be derived on the secondary side of the xfmr.

And I assumed the “480 panels” are 3 phase panels with 277v lighting loads, which require a neutral.
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Primary side? Like utility primary? You ever seen that?

The service entrance is 480/277. Can't have 277 WO neutral, thus genny neutral is required.
 
Seven-Delta-FortyOne said:
But if the generator is feeding to primary side of the transformer, no neutral would be needed, correct?

The neutral would be derived on the secondary side of the xfmr.

And I assumed the “480 panels” are 3 phase panels with 277v lighting loads, which require a neutral.
Click to expand...
The transformer is 480 to 208Y/120 as I understand the installation.
 
fastline said:
Primary side? Like utility primary? You ever seen that?

The service entrance is 480/277. Can't have 277 WO neutral, thus genny neutral is required.
Click to expand...
All transformers have a primary and secondary side, unless you are talking about an autotransformer.
All of my posts have said a neutral conductor from the generator to the transfer switch is required.
 
fastline said:
Like utility primary? You ever seen that?
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Yes, I have worked on a number of services where the service point was on the utility medium voltage circuit with a customer owned transformer to get down to 480 volts.
In one case it was a 10MVA 34.5 KV to 4.16 KV customer owned transformer, with 4.15 KV distribution through out the panel and 4.16 KV to 480 volt transformers supplying the various building, and a few 4.16 KV motor loads. The plant transformers varied from 750 KVA to 2500 KVA.
 
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