ATS netural transfer

[QES]

What is the benefit of having a ATS transfering the netural?
Beside NEC requirement of a separate derive system.

 

[chris kennedy]

A 4 pole ATS cost more, therefore overall job markup is higher.

 

[iwire]

It is needed when you have GFP ahead of the transfer switch or you can have nuisance tripping

 

[brian john]

It is a design issue, with a 4-pole ATS in a 3-phase 4-wire system you bond the neutral at the main service and at the generator. With a 3-pole ATS in the same distribution system you would only bond at the service.

A GFP would operate fine with either system assuming you keep the downstream neutrals free of all ground connections.

Many times when investigating grounding issues we find the neutral bonded at the generator with a 3-pole ATS in a 3-phase 4-wire system and not bonded with a 4-pole ATS.

 

[iwire]

A GFP would operate fine with either system assuming you keep the downstream neutrals free of all ground connections

Not sure of that, I have seen some diagrams showing how even wired properly the GFP can be tripped with the use of a solid neutral switch.

 

[iwire]

If a ground fault occurs while normal power is available
and the generator is supplying power to the load, a
potential exists for a trip of the GFP equipment at
the utility service.

From page 3 here http://www.cumminspower.com/www/literature/technicalpapers/PT-6006-GroundingAC-2.pdf

 

[hillbilly1]

I think it may be because the source voltage is not coming through the ground fault CT, but a fault on the generator supplied load would falsely trip the ground fault main if it is still energized, such as exercising under load. "isolating" the neutral would put the fault behind the CT, instead of through it, so the main would not see the fault of the other system, at least until the transfer :-? back to normal. :-?

 

[hillbilly1]

Hey! you beat me to it!

 

[weressl]

What is the benefit of having a ATS transfering the netural?
Beside NEC requirement of a separate derive system.

Well, let's think about it.

Does the neutral carry current?

If unswitched, how would the respective circuit be completed?

(There are a host of other comments that point to the need, but I think the above is the basic issue.)