Generator and Fire Pump - SDS or not?

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lkdiaZ

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Virgin Islands
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Electrical Contractor
When wiring the generator side of a 3ph/3w Fire Pump Controller we would normally carry 3 phase wires and an EGC to the FPC. We wouldn't carry the neutral to the FPC from the generator because it doesn't require one. However by doing so are we not automatically causing the generator to be an SDS? The normal side of the fire pump controller is a service with 3 phase wires and the neutral brought in as required. If this is the case then wouldn't the generator require that any other load it serves such as a building load be done through the use of a 4 pole ATS and the appropriate bond of N-Gnd at the generator?
 

lkdiaZ

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Location
Virgin Islands
Occupation
Electrical Contractor
Is there an EGC between the fire pump and generator?
There is an EGC between the generator and the Fire Pump Controller.

Here's the point I'm trying to get feedback on. The application is a generator. It has two breakers. One generator breaker feeds the building load via a 3 pole ATS, the other breaker backs up a fire pump. The fire pump is 3ph/3w so it does not need a neutral and one is not brought in from the generator. By not bringing in the neutral of the generator and solidly connecting it to the neutral of the normal source of power at the FPC which in this case is a utility service, the generator is now by definition an SDS. Because it is an SDS we have to bond the neutral and ground at the generator. HOWEVER - if we do this bond at the generator, then we cannot use a 3 Pole ATS for the other generator breaker which feeds a normal building load because you cannot use a 3 pole ATS for a 3ph/4w system with an SDS and therefore the building ATS MUST BE a 4 pole ATS.
 

lkdiaZ

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Location
Virgin Islands
Occupation
Electrical Contractor
Unless I am misunderstanding what you are describing you have no way to isolate the Fire Pump Controller from the utility when the generator comes on line. That would mean another transfer switch is needed.
The fire pump controller is an ATS in itself. It switches between the utility service and the generator.
 

lkdiaZ

Member
Location
Virgin Islands
Occupation
Electrical Contractor
Is there a utility grounded/neutral at the fire pump controller?
Yes.

From utility transformer there are 3 phase wires and a grounded (neutral) conductor running directly to the fire pump controller and from the generator there are 3 phase wires and an equipment ground conductor (EGC) running from one of the generator breakers to the fire pump controller.
 

ActionDave

Chief Moderator
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Durango, CO, 10 h 20 min from the winged horses.
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Licensed Electrician
So what's the reason not to bring a neutral from the generator to the fire pump controller? If you are using metal conduit make that your equipment ground and use your fourth wire as a neutral.

Electrically speaking, since you don't have any neutral loads at the fire pump you could bond your fourth wire at the fire pump and it would function fine but not be code compliant.
 
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