3 Pole ATS's - OUCH

[cleveland]

Here is what we have:

One generator serves a Distribution Panel at 277/480 volt. Individual 4W feeders are run from the DP to 3 pole ATS's in different buildings. The grounded conductor is bonded/grounded at each building. Have we not tied the grounded conductor to ground at several locations? Shouldn't we have used 4 pole ATS's? If so, ouch! We are considering installing a delta-wye transformer at each building so we don't need the grounded conductor at all from the generator or the building service. I am open to other less costly interpretations! And/or solutions.

Thanks,


Jim

 

[raider1]

Are equipment grounding conductors run with the feeders?

Chris

 

[augie47]

and is it a new installation ? installed under what Code cycle ?

 

[chris kennedy]

Are equipment grounding conductors run with the feeders?

Chris

This is your main issue.

Shouldn't we have used 4 pole ATS's?

That is a design issue but I am curious to know if this is 1000 amps or higher.

 

[cleveland]

Equipment grounding conductors were installed as the feeders were in PVC where below grade. Usually these feeeders were in the 100 amp size. The original installation is about two code cycles back. We just added another building to the distribution. We are less than 1000 amps.

 

[augie47]

Ther equipment grounding conductor made life a lot easier.
Unless there is some engineering design need for a 4 pole, you are fine with a 3 pole ATS. The grounded-grounding connection needs to be removed and your grounding condcutor needs to connect to your grounding electrode system.
If your ATS is the 1st equipment at the building and it is not service rated, you need to take a look at 225.32 and the exceptions to see if you are in compliance.

 

[steve66]

Are there separate utility transformers at each building?

If so, I believe a good design should have included 4 pole ATS's at each building. Since you don't have those, there will be multiple neutral-ground bonds on the system, and the ground wires will essentially be in parallel with the neutral wires.

Not a good design, but I'm not sure this violates any code article.

Steve

 

[cleveland]

There are separate utility transformers at each building. When looking at just an outage in one building things looked okay but when we considered a total outage affecting numerous buildings we saw the multiple grounds on the neutrals. What about trying to eliminate the need for that neutral by using a delta-wye transformer at each building? The ATS's are not the 1st equipment in the building. We are only picking up emergency lighting circuits and fire alarm panels etc. in each building.

 

[steve66]

There are separate utility transformers at each building. When looking at just an outage in one building things looked okay but when we considered a total outage affecting numerous buildings we saw the multiple grounds on the neutrals. What about trying to eliminate the need for that neutral by using a delta-wye transformer at each building? The ATS's are not the 1st equipment in the building. We are only picking up emergency lighting circuits and fire alarm panels etc. in each building.

It sounds like you are saying the multiple grounds are only there when there is an outtage. That's not the case - at least not if I understand your setup. With mulitple services and 3 pole ATS's, there are always multiple N-G bonding points in the system, even when running on utility power. So some of your neutral current will always be running back on the ground wires.

I assume you would place a delta to wye transformer at the emergency input to each ATS, and treat it as a non-SDS system. I don't see a problem with that, but others might. I'm wondering if you have to bond the Neutral and ground at the stepdown transformers secondary.

 

[Strife]

Are you talking same service? same meter?
You can install a generator either as a separately derived system, or not. If it's as a separately derived system, you need a 4 pole ATS. If you installed a generator across 3 different meter, then it is a separately derived system, or least, that's how you'll get away on feeding one generator across 3 services. If there's only one service, the three subs shouldn't be bonded grounded to grounding. ????

Here is what we have:

One generator serves a Distribution Panel at 277/480 volt. Individual 4W feeders are run from the DP to 3 pole ATS's in different buildings. The grounded conductor is bonded/grounded at each building. Have we not tied the grounded conductor to ground at several locations? Shouldn't we have used 4 pole ATS's? If so, ouch! We are considering installing a delta-wye transformer at each building so we don't need the grounded conductor at all from the generator or the building service. I am open to other less costly interpretations! And/or solutions.

Thanks,


Jim

 

[cleveland]

It sounds like you are saying the multiple grounds are only there when there is an outtage. That's not the case - at least not if I understand your setup. With mulitple services and 3 pole ATS's, there are always multiple N-G bonding points in the system, even when running on utility power. So some of your neutral current will always be running back on the ground wires.

I assume you would place a delta to wye transformer at the emergency input to each ATS, and treat it as a non-SDS system. I don't see a problem with that, but others might. I'm wondering if you have to bond the Neutral and ground at the stepdown transformers secondary.

Steve,

Yes you are correct. I was trying to explain that we didn't see the problem until we stepped back a bit and looked at the overall site one-line. Just looking at one building you'd not notice the other grounded conductors. At least we didn't; like I said - OUCH! I think we'd want to/have to bond the grounds and neutral on the secondary side of the step down transformers. But wouldn't the delta connection on the primary eliminate the ground currents issue on the emergency distribution?

 

[steve66]

Steve,

Yes you are correct. I was trying to explain that we didn't see the problem until we stepped back a bit and looked at the overall site one-line.

Yes, it's a really tough problem to see, even with a complete one line.

But wouldn't the delta connection on the primary eliminate the ground currents issue on the emergency distribution?

Yes, it would. But see my comment below.

I think we'd want to/have to bond the grounds and neutral on the secondary side of the step down transformers.

With a three pole transfer switch, it seems like the transformer would be a non-SDS. In that case, wouldn't you just have the Neutral-Ground bond at the main utility service? Then the transformer would be using that bonding connection. I'm not sure if that's a code compliant installation? Maybe someone else knows? Can you install a transformer as a non-SDS?

On the other hand, if you do bond the N-G together at the stepdown transformer, you will still have 2 N-G bonds inside each building. One at the main utility service, and one at the stepdown xformer.

So within that building, you will still have the neutral and ground wires paralleled on the ATS feeders. You've eliminated the problems going back to the generator, and made things better, but there is still an issue inside each building.

Steve

 

[cleveland]

With a three pole transfer switch, it seems like the transformer would be a non-SDS. In that case, wouldn't you just have the Neutral-Ground bond at the main utility service? Then the transformer would be using that bonding connection. I'm not sure if that's a code compliant installation? Maybe someone else knows? Can you install a transformer as a non-SDS?

On the other hand, if you do bond the N-G together at the stepdown transformer, you will still have 2 N-G bonds inside each building. One at the main utility service, and one at the stepdown xformer.

So within that building, you will still have the neutral and ground wires paralleled on the ATS feeders. You've eliminated the problems going back to the generator, and made things better, but there is still an issue inside each building.

Steve

Hmmmmmmmm........ If we install the delta-wye transformer we should eliminate the need for a 4 pole ATS. Now the neutral current and connections are being resolved on the SDS
of the transformer secondary. The neutral current is resolved right there. Isn't this a typical dry-type step down transformer connection we use everyday? Yes we have the neutral bonded to ground and bonded to building steel and yes we have utility transformers upstream. But we can do this.

 

[RUWired]

Then the transformer would be using that bonding connection. I'm not sure if that's a code compliant installation? Maybe someone else knows? Can you install a transformer as a non-SDS?

On the other hand, if you do bond the N-G together at the stepdown transformer, you will still have 2 N-G bonds inside each building. One at the main utility service, and one at the stepdown xformer.


Steve

Steve the transformer would go between the transfer switch and the load panel at each additional building, not between the generator distribution panel and the transfer switch.

Rick

 

[steve66]

Hmmmmmmmm........ If we install the delta-wye transformer we should eliminate the need for a 4 pole ATS. Now the neutral current and connections are being resolved on the SDS
of the transformer secondary. The neutral current is resolved right there. Isn't this a typical dry-type step down transformer connection we use everyday? Yes we have the neutral bonded to ground and bonded to building steel and yes we have utility transformers upstream. But we can do this.

With a 3 pole ATS, you normally bond the Neutral and Ground only at the service entrance. Not at the generator.

Now you are basically proposing to replace the generator with a step down transformer. But the transformer will have the N-G bond that isn't allowed at the generator. It doesn't seem quite right to me. But not bonding the N-G at a stepdown transformer doesn't feel right either. Does that mean a 4 pole ATS is always required when the generator voltage runs through an xformer?? I'm not sure.

Steve the transformer would go between the transfer switch and the load panel at each additional building, not between the generator distribution panel and the transfer switch.

Rick

I'm not sure how that would help any grounding issues, so I am assuming the OP means the xformer is on the emergency input to the ATS??? If you are right, what I'm saying wouldn't apply at all.

Oh, and sorry - I started calling it a stepdown xformer, when we are all really talking about 1:1 xformer.

Steve

 

[RUWired]

Steve, if the transformer is placed on the generator output, the system bonding jumper would place the equipment ground and grounded conductor in parallel once again like you said in post 12.

If the transformer is placed on the load side of the ATS in each additional building, the parallel N/G would be eliminated because the secondary transformer bonding jumper is not directy tied to any downstream N/G connections.

The grounded conductor from the generator output to the ATS that was causing the parallel N/G connection would not be needed.

Rick

 

[steve66]

Steve, if the transformer is placed on the generator output, the system bonding jumper would place the equipment ground and grounded conductor in parallel once again like you said in post 12.

If the transformer is placed on the load side of the ATS in each additional building, the parallel N/G would be eliminated because the secondary transformer bonding jumper is not directy tied to any downstream N/G connections.

The grounded conductor from the generator output to the ATS that was causing the parallel N/G connection would not be needed.

Rick

I'm following what you are saying now. Yes, you are probably right - that's what the OP is probably planning on doing. It hadn't occured to me that since the xformer doesn't need the grounded conductor, the grounded conductor doesn't need to be landed on the the xfer switch.

But I mentioned a few posts ago that I was assuming the xformer was on the emergency input to the ATS, and the OP didn't correct me. But maybe the OP just missed that comment.

Steve

 

[cleveland]

Sorry, I got spirited away for a few days. The delta-wye transformer will be the first device on the load side of the 3 pole ATS. Both normal and now the emergency will be 480 volt 3 phase 3 wire plus equipment ground.