generators 4 poles switching

[Ed MacLaren]

Re: generators 4 poles switching

Chuck,
As Dereck has stated, without GFP installed at the service, the generator system can be SDS or non-SDS.

The determining factor is often the internal connections of the generator, specifically, whether the winding center-tap (neutral) is bonded to the frame or not.

Because small portable "stand-alone" generators are required to have the neutral-frame bond connection when used with cord-connected loads, the trouble arises when someone connects one of these, through a transfer switch, to a facility system, without switching the neutral, or removing the neutral-frame bond connection.

Ed

 

[Ed MacLaren]

Re: generators 4 poles switching

Chuck,
With regard to your question regarding Ground Fault Protection, this sketch may help illustrate what Dereck has stated above, about trying to use a non-SDS stand-by system with GFP.

While a section of a facility was on generator power, a ground fault in the generator feeder might trip out the main and black-out other sections of the facility.

Ed

 

[dereckbc]

Re: generators 4 poles switching

Thanks Ed for drawing it out. That is precisely what I was referring to.

 

[bennie]

Re: generators 4 poles switching

Connect the transfer switch and generator on the supply side of the service switch. Everything will be normal on both power sources.

 

[iwire]

Re: generators 4 poles switching

Bennie,
What if I do not want pick up the whole building on the generator?

 

[bennie]

Re: generators 4 poles switching

Operating a generator supplying part of the load, with both sources energized, in the transfer switch, is not a recommended long duration procedure.

The GFP will trip under normal power in the event of a fault.

Now show the switching neutral drawing.

 

[bennie]

Re: generators 4 poles switching

FPN No.1: 250.20 is a contradiction of the definition of a separately derived system.

The handbook description, of separately derived systems, is not in line with the description in the NEC archives.

The changes in the code book are by the same individuals that state every transformer is a separately derived system except an auto-transformer.

How about a grounded wye/grounded wye? There is an MGN connected to both windings.

How about an ungrounded wye auto-transformer? There is no grounded neutral.

How about an ungrounded delta auto-transformer? There is no grounded neutral

How about a grounded wye/grounded delta? There is a MGN conductor.