ATS Closed transition Neutral switching

[faresos]

For 1200A @ 480/277V, service entrance with Bypass-isolation switch, Closed transition; I spoke to a vender and he recommended to use solid neutral type, my understanding for this application, since we have GFP for the breaker at the ATS, we need to use 4-Pole ATS (switched neutral) in lieu of 3-pole to avoid nuisance tripping. (The generator will be separately derive system). Any thoughts ? Thanks,

 

[iceworm]

For 1200A @ 480/277V, service entrance with Bypass-isolation switch, Closed transition; I spoke to a vender and he recommended to use solid neutral type, my understanding for this application, since we have GFP for the breaker at the ATS, we need to use 4-Pole ATS (switched neutral) in lieu of 3-pole to avoid nuisance tripping. (The generator will be separately derive system). Any thoughts ? Thanks,

One thought: Why make the gen an SDS? Remove the N-G bond and feed a 3 pole ATS 5 wire.

Then again, I don't know what a "service entrance with Bypass-isolation switch" is, so maybe I don't understand.

I deal with a lot of multiple generator or generator/utility systems. Never use a 4 pole ATS. If fact rarely use an ATS - almost always 3pole CBs in a switchboard for each feed.

ice

 

[brian john]

I THOUGT the 4 pole ATS that were close transistion had an over lapping neutral for transfers?

The other option is as noted above is lift the neutral ground bond at the generator. You should verify the neutral is not grounded in either system including downstream from the ATS and the GFPE will not have a tripping issue ( from multiple grounds on the neutral).

 

[ron]

If the gen will have GFP, then I suggest a 4 pole ATS. In order to use a 4 Pole ATS, you need the gen to be a SDS.

 

[steve66]

The last generator seminar I was at, they said you should use a 4 pole ATS if you have GFP.

Otherwise, your risk either desentizing the GF, or causing nuicense trips. Even if you only have a single N-G bond.

I'm not 100% sure they were correct. It may well depend on the type of GF sensor you have.

 

[brian john]

The last generator seminar I was at, they said you should use a 4 pole ATS if you have GFP.

Otherwise, your risk either desentizing the GF, or causing nuicense trips. Even if you only have a single N-G bond.

I'm not 100% sure they were correct. It may well depend on the type of GF sensor you have.

They'd have a lot of drawing and answering for that statement before I'd accept it. Maybe their firm only sells 4-pole ATS's?

 

[iceworm]

If the gen will have GFP, then I suggest a 4 pole ATS. In order to use a 4 Pole ATS, you need the gen to be a SDS.

The last generator seminar I was at, they said you should use a 4 pole ATS if you have GFP.

Otherwise, your risk either desentizing the GF, or causing nuicense trips. Even if you only have a single N-G bond.

I'm not seeing the need for a 4 pole. here is my reasoning:
Keep in mind I work industrial exclusively. Rarely use transfer switches - almost always use two CBs in switchgear.

View attachment 3 pole non-sds.pdf
The only issue is the utility generally mandates an N-G bond at the xfm (if it is their xfm). One has to arrange the N-G bond is ahead of the GF window. And that would be an issue even if one used a 4pole.

If I'm screwed up, help me out. What am I missing?

ice

 

[ATSman]

For 1200A @ 480/277V, service entrance with Bypass-isolation switch, Closed transition; I spoke to a vender and he recommended to use solid neutral type, my understanding for this application, since we have GFP for the breaker at the ATS, we need to use 4-Pole ATS (switched neutral) in lieu of 3-pole to avoid nuisance tripping. (The generator will be separately derive system). Any thoughts ? Thanks,

http://cumminspower.com/www/literature/technicalpapers/PT-6006-GroundingAC-2-en.pdf

 

[iceworm]

http://cumminspower.com/www/literature/technicalpapers/PT-6006-GroundingAC-2-en.pdf

Yes, that is an interesting paper. Amazingly, it pretty well supports my position:

From the Cummins paper
.

“Where ground fault protection is provided for the
service disconnecting means and interconnection
is made with another supply system by a transfer
device, means or devices may be needed to
assure proper ground fault sensing by the ground
fault protection equipment.”
—NEC Article 230-95(C) Fine Print Note No. 3​

.

The Fine Print Note calls attention to the need for a
4-pole transfer switch (a transfer switch with a switched
neutral pole) or if 3-pole transfer switches are used that
the generator neutral should not be grounded a second
time at the generator on the load side of the normal
service disconnecting means.​

.
Definitely one bond - one place, no more. Yes, the NEC occasionally insists on multiple bonding connections - which result is neutral current paralleled over the grounding interconnections. I don't know what to say about that. (actually I do know what to say - but i won't. :rant

And, there are a few places where a 4-pole switch is required. This is not one.

Still, I'm listening - today is a good day to learn.

ice

 

[steve66]

They'd have a lot of drawing and answering for that statement before I'd accept it. Maybe their firm only sells 4-pole ATS's?

I knew you would be skeptical I'm not sure I'm sold either.

But no, they don't just make 4 pole ATS's. The person who made that statement was from Cummins - it might have even been Jim Iverson who is listed the paper ATSman posted a link to, but I don't remember his name.

However, I notice the paper makes a specific reference to zero squence GF protection, and recommends 4 pole ATS's anytime that is a possibility. At the seminar, they didn't really have time to go into details about the 2 different types of GF protection.

 

[ATSman]

I knew you would be skeptical I'm not sure I'm sold either.

But no, they don't just make 4 pole ATS's. The person who made that statement was from Cummins - it might have even been Jim Iverson who is listed the paper ATSman posted a link to, but I don't remember his name.

However, I notice the paper makes a specific reference to zero squence GF protection, and recommends 4 pole ATS's anytime that is a possibility. At the seminar, they didn't really have time to go into details about the 2 different types of GF protection.

I would just like to add here there are actually 3 types of GFR protection systems used in the US:

Zero Sequence: One CT around all current carrying conductors
Residual: Separate CTs " " " " "
Ground Return or Ground Strap: One CT around the neutral to ground bond (strap.)

The 3 are described in this link starting on P. 5 :

http://www.geindustrial.com/publibr...7?TNR=Application and Technical|GEI-48907|PDF

Tony