Do I need a 4 pole ATS?

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qcroanoke

qcroanoke

Sometimes I don't know if I'm the boxer or the bag
Location
Roanoke, VA.
Occupation
Sorta retired........
Have an installation where we have 120/208 3 phase service coming into the building. We also have a 200 kw genset with dual outputs 1- 400 amp output 1- 200 amp output.
Here's where it gets interesting. Generator output is 120/240 3 phase delta (high leg). 400 amp output will feed delta loads.
200 amp output will feed delta/wye transformer creating a SDS that will feed our loads through the ATS. We will most likely bond in the Xfmr. Thereby creating 2 bonded systems in the same ATS.
I'm pretty sure I already know the answer to this, but, do I need a 4 pole ATS to switch the neutrals to meet code?
Or is there an alternative to a 4 pole switch?
THANKS!
 
qcroanoke said:
Have an installation where we have 120/208 3 phase service coming into the building. We also have a 200 kw genset with dual outputs 1- 400 amp output 1- 200 amp output.
Here's where it gets interesting. Generator output is 120/240 3 phase delta (high leg). 400 amp output will feed delta loads.
200 amp output will feed delta/wye transformer creating a SDS that will feed our loads through the ATS. We will most likely bond in the Xfmr. Thereby creating 2 bonded systems in the same ATS.
I'm pretty sure I already know the answer to this, but, do I need a 4 pole ATS to switch the neutrals to meet code?
Or is there an alternative to a 4 pole switch?
THANKS!
Click to expand...

You already called it. If you bond gen you have to switch neutral to avoid parallel paths
 
qcroanoke said:
Have an installation where we have 120/208 3 phase service coming into the building. We also have a 200 kw genset with dual outputs 1- 400 amp output 1- 200 amp output.
Here's where it gets interesting. Generator output is 120/240 3 phase delta (high leg). 400 amp output will feed delta loads.
200 amp output will feed delta/wye transformer creating a SDS that will feed our loads through the ATS. We will most likely bond in the Xfmr. Thereby creating 2 bonded systems in the same ATS.
I'm pretty sure I already know the answer to this, but, do I need a 4 pole ATS to switch the neutrals to meet code?
Or is there an alternative to a 4 pole switch?
THANKS!
Click to expand...
If all the 200A output feeds is the delta/wye transformer's primary, you do not need a 4-pole ATS because you shouldn't even be running a grounded conductor. If you bond the genset's neutral tap. You have met the requirement for grounding this system. The transformer may also be a grounded SDS but it's secondary is electrically isolated from (i.e. not solidly interconnected with) the primary. Yes the two will be interconnected via their grounding but there is nothing wrong with that. It provides a path for ground fault current, for whichever system is the source of the fault.

Just to make sure we are covering all the bases, what is the service voltage and configuration, and where in the system are the ATS's being located?
 
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The OP will need a switched neutral in the transfer switch feeder circuit providing he is running a grounded conductor on the secondary side of the transformer because the system bonding jumper in the transformer and in the service main will put the neutral and ground in parallel. The transfer switch with only the 3-wire feeder only needs to be a solid neutral switch. Since both loads are 3-wire from the gen set it needs to be a SDS.
 
Pierre C Belarge said:
Why would he need the 4-pole switch?
Click to expand...
I don't know that he does. I'm of the [strong] impression he does not.

Pierre C Belarge said:
Why does he need to wire the generator as a separately derived system to start with?
Click to expand...
He doesn't... but the genset's output is req'd to be a grounded system, which can be accomplished by either a solid-connected-to-service-system grounding conductor?thereby NOT an SDS, and the neutral tap would not be bonded to ground at the generator?or by making it an SDS and bonding the neutral tap of the genset to it's GEC and having no grounded conductor run to the ATS's. In either case, a 4-pole ATS isn't req'd. In fact, a 4-pole ATS is never req'd. It is only when someone for some reason decides it is a better design to bond the grounded conductor at the generator. The reasoning behind that decision escapes me :)
 
Smart $ I agree with your post but as you stated we don?t know all the facts as to his setup. The OP did state the service was120/208 3 phase serving the building.
So I am going to toss this out and assume there are two transfer switches? If so, on the 200 amp feed wouldn?t the transfer switch have to be on the secondary side of the delta/wye transformer? Otherwise the transformer primary would be connected to the common terminal of the transfer switch, between the transfer switch and the load which would not work in this scenario. With the generator connected to the primary of the transformer we then have a generator to transformer to transfer switch to load with a grounded conductor between the transformer and transfer switch. In this case only a three pole switched would be required provided there is no GFPE in the system.
The 400 amp load in feeding only line to line loads. No grounded conductor to switch, again only a three pole switch. OC protection is not addressed in this post.
 
Mvillines said:
Smart $ I agree with your post but as you stated we don?t know all the facts as to his setup. The OP did state the service was120/208 3 phase serving the building.
So I am going to toss this out and assume there are two transfer switches? If so, on the 200 amp feed wouldn?t the transfer switch have to be on the secondary side of the delta/wye transformer? Otherwise the transformer primary would be connected to the common terminal of the transfer switch, between the transfer switch and the load which would not work in this scenario. With the generator connected to the primary of the transformer we then have a generator to transformer to transfer switch to load with a grounded conductor between the transformer and transfer switch. In this case only a three pole switched would be required provided there is no GFPE in the system.
The 400 amp load in feeding only line to line loads. No grounded conductor to switch, again only a three pole switch. OC protection is not addressed in this post.
Click to expand...


I also agree, but with limited knowledge of what this install really looks like.

Again, it would be easier to relay info if there was/is some kind of drawing.
Othewise we are just guessing at the installation.

Most times, the generator wiring is not installed as a separately derived install. I wonder if the install has any engineering behind it???
 
Pierre C Belarge said:
This is where a drawing would really help.
Click to expand...

Surely would. I considered drawing one up but I would like my question regarding service configuration and ATS location answerd first.

Another question needs answered, too. Is this a dual output or split output genset? The OP uses the term dual output. To me, dual output is two separate sources... whereas a split output is a single source supplying more than one OCPD.
 
Mvillines said:
...The OP did state the service was120/208 3 phase serving the building.
Click to expand...
Ooops! ...missed that. :rolleyes:

Mvillines said:
So I am going to toss this out and assume there are two transfer switches? If so, on the 200 amp feed wouldn’t the transfer switch have to be on the secondary side of the delta/wye transformer?
Click to expand...
Well he said, "200 amp output will feed delta/wye transformer creating a SDS that will feed our loads through the ATS." On first read, I took that to mean the 200A output fed the xfmr through the ATS. Now that I re-read it, I'm not so sure.

Mvillines said:
Otherwise the transformer primary would be connected to the common terminal of the transfer switch, between the transfer switch and the load which would not work in this scenario.
Click to expand...
Your quite right ;) [...and that leads to my last few questions below]


Mvillines said:
With the generator connected to the primary of the transformer we then have a generator to transformer to transfer switch to load with a grounded conductor between the transformer and transfer switch. In this case only a three pole switched would be required provided there is no GFPE in the system.
Click to expand...
Well, at least we're back to a 4-pole ATS not being req'd... but I have to ask why we would need one if there was GFPE in the system?

Mvillines said:
The 400 amp load in feeding only line to line loads. No grounded conductor to switch, again only a three pole switch. OC protection is not addressed in this post.
Click to expand...
Well both outputs are feeding only 3? 3W loads... but here is where I have to ask is there not a xfmr on the 400A output? If not, that would be mixing two different voltage systems, right? ...and are all connected loads [now and in the future] dual rated 208/240?

Sounds like somebody ordered the wrong generator!!! Either that or they are trying to make use of one already on hand.
 
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Pierre C Belarge said:
Here is an ECM article about this topic.
You can probably scroll to the bottom of the article first.
Click to expand...

Well I went to the bottom and couldn't believe my eyes... references to FPN's under a requirement for sevices. So I went up further and I see why...

Note Figures 1 and 2 have both a solidly-connected grounding conductor AND a bonded neutral terminal at the genset [and calling the genset an SDS, yet the article says a genset with a solidly-connected grounding conductor is not an SDS... talk about contradiction!!!]. Who bonds at the genset when running a solidly-connected-to-service-system grounded conductor??? Don't they know they are creating a parallel neutral current path??? That wasn't even mentioned in the article AFAICT!!!
 
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I think you gentlmen missed the jest of what is was saying about the requirement of the transfer switch. The key is the placement of the transformer. If the OP puts the transformer before the transfer switch (as he stated) the system bonding jumper of the transformer and the service main jumper will put the neutral and ground in parallel, thereby requiring the 4-pole switch. If the OP installs the transformer after the transfer switch, a solid neutral switch will be ok.
Rick
 
RUWired said:
I think you gentlmen missed the jest of what is was saying about the requirement of the transfer switch. The key is the placement of the transformer. If the OP puts the transformer before the transfer switch (as he stated) the system bonding jumper of the transformer and the service main jumper will put the neutral and ground in parallel, thereby requiring the 4-pole switch. If the OP installs the transformer after the transfer switch, a solid neutral switch will be ok.
Rick
Click to expand...

The above is what we are doing. The xfmr will be before the transfer switch.
I guess I could have been a little more clear on what we are doing. Also I said dual output of the generator not split output. To clarify both outputs are 240 delta. The 400 amp output will feed delta loads.
The 200 amp output will feed the xfmr to OCP to the ATS to the 120/208 3 phase loads.
Building incoming service is 200 amp 120/208 3 phase.
The reason for the delta generator is our building will be located in a water plant and they
want the generator to supply their loads as well as ours. I assume they will install their own ATS for their loads. That is not my concern.
My concern is do I or do I not have to switch the neutral in our ATS?
Hope this answered your questions.
 
RUWired said:
I think you gentlmen missed the jest of what is was saying about the requirement of the transfer switch. The key is the placement of the transformer. If the OP puts the transformer before the transfer switch (as he stated) the system bonding jumper of the transformer and the service main jumper will put the neutral and ground in parallel, thereby requiring the 4-pole switch. If the OP installs the transformer after the transfer switch, a solid neutral switch will be ok.
Rick
Click to expand...

If the generator feeds the transformer, and the transformer feeds a 3 pole switch: then I don't see why you would bond the transformer ground and neutral. The neutral (at the transformer) would be solidly connected to the service neutral, and the ground (at the transformer) would be solidly connected to the service ground.

Seems to me the N-G bond at the service would be the only one required.

Steve
 
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