3 pole vs 4 pole ATS's

[mshields]

I have long been in the habit of specing 4 pole ATS's and treating the generator as a SDS; requiring that the contractor bond neutral to ground at the generator.

On a relatively small system I'm doing for a small 6 unit apt building, we're putting in a 208Y/120V generator for standby loads (they will still have EBU's for emergency lighting).

I speced, as is my habit a 4 pole ATS and showed a neutral to ground bond at the generator. I know this is fine, but I also know that 4 pole ATS's are more expensive.

Is there any reason not to go with a 3 pole ATS (so long as we don't bond N to G at the generator? The load is a mix of 3 phase motors and single phase lighting loads.

Thanks,

Mike

 

[chris kennedy]

I see no reason to spec a 4 pole unless 1000A @ 480V and over.

 

[mshields]

yeah -= thought so

yeah -= thought so

thanks,

Mike

 

[infinity]

I see no reason to spec a 4 pole unless 1000A @ 480V and over.

Chris can you explain why?

 

[chris kennedy]

GFP.

 

[Strathead]

I have long been in the habit of specing 4 pole ATS's and treating the generator as a SDS; requiring that the contractor bond neutral to ground at the generator.

On a relatively small system I'm doing for a small 6 unit apt building, we're putting in a 208Y/120V generator for standby loads (they will still have EBU's for emergency lighting).

I speced, as is my habit a 4 pole ATS and showed a neutral to ground bond at the generator. I know this is fine, but I also know that 4 pole ATS's are more expensive.

Is there any reason not to go with a 3 pole ATS (so long as we don't bond N to G at the generator? The load is a mix of 3 phase motors and single phase lighting loads.

Thanks,

Mike

Out of curiosity, why did you get in that habit in the first place? I often wonder why Engineers specify more expensive material and methods as a rule regardless of the project.

 

[ron]

I agree with Chris. I would add that if you need GFP AND you need a neutral downstream.

My habit is try to leave the neutral at the generator (N-G bond) if practical and then downstream I don't have to worry about 4 pole (or 3) XFER switches

 

[mshields]

Ron - not sure what you meant by that last one

Ron - not sure what you meant by that last one

If you bond at the generator, you need 4 pole switch

If you don't make that bond and you don't have ground fault at the generator (i.e. owing to 480V and 1000V), then only 3 pole is needed.

But what I don't see is a situation where you can bond or not bond at the generator and be safe with either a 3 pole or a 4 pole switch?

Thanks,

Mike

 

[ron]

If you bond at the generator, you need 4 pole switch

If you don't make that bond and you don't have ground fault at the generator (i.e. owing to 480V and 1000V), then only 3 pole is needed.

But what I don't see is a situation where you can bond or not bond at the generator and be safe with either a 3 pole or a 4 pole switch?

Thanks,

Mike

Mike, If you bond at the generator, and do not bring a neutral downstream in the power path (only phases and EGC), then there is never a need for a 4 pole switch, because there is no neutral to switch.

 

[iwire]

Mike, If you bond at the generator, and do not bring a neutral downstream in the power path (only phases and EGC), then there is never a need for a 4 pole switch, because there is no neutral to switch.

I must be misunderstanding you.

The fact a load may not use a neutral does not change the need for a four pole switch.

 

[infinity]

So if you have GFP at the generator switchboard then you would need a 4-pole ATS. Is it required for a generator?