3 Phase 3 Wire Generator

Dsg319

Senior Member
Location
West Virginia
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Journeyman Electrician
I know this doesn’t answer your question? But out of curiosity, is genset the only source of power, or is there grid power present to. Genset floating or bonded? Or is it straight ungrounded delta wound generator no neutral... I don’t even know if that is such a thing but.. figured I’d ask.
 
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mbrooke

Batteries Not Included
Location
United States
Occupation
Electricity
I know this doesn’t answer your question? But out of curiosity, is genset the only source of power, or is there grid power present to. Genset floating or bonded? Or is it straight ungrounded delta wound generator no neutral... I don’t even know if that is such a thing but.. figured I’d ask.

Grid power. Bonded neutral. Wye connection.
 

Dsg319

Senior Member
Location
West Virginia
Occupation
Journeyman Electrician
Do you have a neutral solidly connected through your ATS or just an EGC from the genset with straight 3wire delta loads fed from it?
 

Dsg319

Senior Member
Location
West Virginia
Occupation
Journeyman Electrician
EGC, all loads are 3 wire. No noodle.
I would venture to say no grounding electrodes needed. Being that it’s grounded at the service and you are not altering/ switching the the grounded conductor in the ATS, it would be considered a non-SDS.

We’ll see what others have to say. But that’s my take.

The only questionable thing I have is being bonded both at the service and the generator, BUT being that there is no neutral pulled from the genset and no line to neutral loads. I don’t see a way for objectionable current to ever be present.
 

mbrooke

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Location
United States
Occupation
Electricity
I would venture to say no grounding electrodes needed. Being that it’s grounded at the service and you are not altering/ switching the the grounded conductor in the ATS, it would be considered a non-SDS.

We’ll see what others have to say. But that’s my take.
Thanks. Curious to see what others think.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
On the opening question: I don't see the generator as requiring it's own grounding electrodes, however I would expect the metal frame of the unit to be connected to an egc, thereby bonding it to the building grounding electrode system.

Separate question: if you have a 3 phase 3 wire generator and a 3 phase grounded wye utility source connected to the ATS, don't you have the problem of being a grounded system on utility power but ungrounded on generator power?

Jon
 

Dsg319

Senior Member
Location
West Virginia
Occupation
Journeyman Electrician
On the opening question: I don't see the generator as requiring it's own grounding electrodes, however I would expect the metal frame of the unit to be connected to an egc, thereby bonding it to the building grounding electrode system.

Separate question: if you have a 3 phase 3 wire generator and a 3 phase grounded wye utility source connected to the ATS, don't you have the problem of being a grounded system on utility power but ungrounded on generator power?

Jon
Correct me if I’m wrong, (very good chance I am) but the genset is indeed bonded-neutral to case. Grounded through the EGC or SSBJ which ever it is in his scenario connecting to grid system neutral solidly.

3phase genset with capability of utilizing a neutral but all loads are straight 480v line to line loads so no need in pulling the neutral? So technically still grounded system on generator?
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
Correct me if I’m wrong, (very good chance I am) but the genset is indeed bonded-neutral to case. Grounded through the EGC or SSBJ which ever it is in his scenario connecting to grid system neutral solidly.
I probably misread, but I heard '3 phase 3 wire generator' and heard 'delta' in my head. Though I expect you are actually correct and that the generator has a wye alternator. I presume it could be bonded or not, though for this application it should be bonded.

Jon
 

Dsg319

Senior Member
Location
West Virginia
Occupation
Journeyman Electrician
I probably misread, but I heard '3 phase 3 wire generator' and heard 'delta' in my head. Though I expect you are actually correct and that the generator has a wye alternator. I presume it could be bonded or not, though for this application it should be bonded.

Jon
Yep. I understand what you mean as when you see 3phase 3wire your mind automatically wants to go to ungrounded delta lol.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
Electricity
I probably misread, but I heard '3 phase 3 wire generator' and heard 'delta' in my head. Though I expect you are actually correct and that the generator has a wye alternator. I presume it could be bonded or not, though for this application it should be bonded.

Jon

Yes, wye alternator. 277/480, but no 277 volt loads.

However, not that you say it, what if the windings were delta or high impedance grounded?
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
IMHO it is preferable that the grounding of the alternative source match that of the primary source. But I don't think this is a requirement.

If your main supply is grounded wye but your generator ungrounded delta, then you would need to comply with things like ground fault detection requirements.

And I imagine there are loads that play differently with different source grounding. Eg. VFDs with input surge protection or systems that are faulted but functional with one type of grounding.

Jon
 

mbrooke

Batteries Not Included
Location
United States
Occupation
Electricity
IMHO it is preferable that the grounding of the alternative source match that of the primary source. But I don't think this is a requirement.

If your main supply is grounded wye but your generator ungrounded delta, then you would need to comply with things like ground fault detection requirements.

And I imagine there are loads that play differently with different source grounding. Eg. VFDs with input surge protection or systems that are faulted but functional with one type of grounding.

Jon

Lets say both were ungrounded- where would the ground detector be?
 
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