Do I need a 4 pole ATS?

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Good job on the diagrams Smart$. That really helps.

I have always been under the impression that the N-G bonding determines if you have an SDS. If it shares the utility N-G bond, it is NOT a SDS. If it has its own N-G bond, then it is an SDS.

I'm not 100% sure if that is correct. But I think I have developed that idea from reading posts from other forum members. I'm supprised that a few of them haven't expressed their view on this subject.

Steve
 
Let?s see if we come to a consensus on a 3 pole switch vs. 4 pole switch.

Typically a transformer is a SDS because we bond the neutral to ground, thus a SDS. I like qcroanoke?s diagram (Attachment 3045) and want to say that?s the way to go without any modifications. Now we would have to arrive that the transformer is NOT a SDS (new one on me). Everything looks good, transformer doesn?t meet the definition of a SDS and now we don?t have to worry about the open neutral during transfer. This looks safe and meets the intent. At first I was having trouble with 250.24(A)(5), then realized that this is not on the load side of the service disconnect it?s on the load side of the generator.

I vote for the drawing on post #35 (Attachment 3045), 3 pole switch.

Give us your vote. Your opinion is as good as the others.
 
Mvillines said:
Let’s see if we come to a consensus on a 3 pole switch vs. 4 pole switch.

Typically a transformer is a SDS because we bond the neutral to ground, thus a SDS. I like qcroanoke’s diagram (Attachment 3045) and want to say that’s the way to go without any modifications. Now we would have to arrive that the transformer is NOT a SDS (new one on me). Everything looks good, transformer doesn’t meet the definition of a SDS and now we don’t have to worry about the open neutral during transfer. This looks safe and meets the intent. At first I was having trouble with 250.24(A)(5), then realized that this is not on the load side of the service disconnect it’s on the load side of the generator.

I vote for the drawing on post #35 (Attachment 3045), 3 pole switch.

Give us your vote. Your opinion is as good as the others.
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Thanks, but that was Smart $'s Diagram.
I like the idea that this is not an SDS and that's the way I vote. But let's hear from the inspectors on this board.
Would you as an inspector accept Smart $'s drawing and not declare it an SDS?
The installation we are discussing will be a long way from where the building will be built
and I don't want a local telling me our install is wrong and will not be accepted and we need a 4 pole ATS along with everything else an SDS requires to be compliant.
Thanks.
 
Qcroanoke no matter what you read here have the local inspector sign off on this before purchasing the transfer switch. Also, depending on the specific location of each piece of equipment could have an effect on sizing the grounded and grounding conductor. I have been practicing as an inspector for the past 23 years, I say practicing because I?m still learning. In fact this is the first time I have encountered this type installation, so it?s all new. You could go with a 4 pole switch and comply with no problems but I can?t find anything to prevent the 3 pole switch as drawn. That?s how I made my decision. If someone proves otherwise, then I have learned something new again.
 
250.142(a)

250.142(a)

Steve and Smart$, here is something to think about. Take a look at 250.142(A) and see if this would apply. The neutral from the transformer to the service main bonding jumper is a grounded conductor. In 250.142 it says the grounded conductor can only be used to ground non-current carrying parts only at the 3 locations listed. If the use of the grounded conductor does'nt fit any of the 3 items listed, then it would be a violation to use the grounded conductor in the manner you dscribe.
Rick
 
RUWired said:
Steve and Smart$, here is something to think about. Take a look at 250.142(A) and see if this would apply. The neutral from the transformer to the service main bonding jumper is a grounded conductor. In 250.142 it says the grounded conductor can only be used to ground non-current carrying parts only at the 3 locations listed. If the use of the grounded conductor does'nt fit any of the 3 items listed, then it would be a violation to use the grounded conductor in the manner you dscribe.
Rick
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The grounded circuit conductor, as depicted in my connection diagrams, is not being used for grounding of any equipment... 250.142 does not apply.
 
Smart $ said:
The grounded circuit conductor, as depicted in my connection diagrams, is not being used for grounding of any equipment... 250.142 does not apply.
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It sure is being used to ground the equipment of the transformer via the bonding jumper in the service equipment. Take away the neutral, is the transformers secondary grounded (no). Can the transformers overcurrent device trip without the neutral being tied to ground (no). Then the grounded conductor is being used to ground the secondary of the transformer.

rick
 
RUWired said:
It sure is being used to ground the equipment of the transformer via the bonding jumper in the service equipment. Take away the neutral, is the transformers secondary grounded (no). Can the transformers overcurrent device trip without the neutral being tied to ground (no). Then the grounded conductor is being used to ground the secondary of the transformer.

rick
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System grounding and equipment grounding are separate issues.
 
Smart $ said:
System grounding and equipment grounding are separate issues.
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exactly and we are. and 250.142 are talking about system grounding. without using the grounded conductor in the manner you describe the transformer will not have its system grounded. you need the system bonding jumper for the transformer to work.your using the grounded conductor to tie the system to ground.
 
250.142 probably don?t apply at all. 250.142(A)(1) doesn?t apply. Transformer or disconnect is not on the supply side of the service. (3) Don?t apply same reason as (1) and this is not a SDS. (2) Could apply if you are using pre 2008 code and then it would be optional.

250.142 states shall be permitted. That means if applicable you are permitted to use the section or you could choose not too.

I ask, if the wye secondary winding was, instead, a generator would you have a problem with this scheme?
 
if the wye secondary winding was, instead, a generator would you have a problem with

if the wye secondary winding was, instead, a generator would you have a problem with

I have been following this thread in attempts to learn in an area which I have quite limited knowledge, and with the question posed by Mvillines :

" I ask, if the wye secondary winding was, instead, a generator would you have a problem with this scheme? "

... got me to thinking, so I just redrew the Smart$'s schematic as shown below...

I am hoping this is helpful, since I am dying to hear the final verdict on this...

mweaver
 
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RUWired said:
Steve and Smart$, here is something to think about. Take a look at 250.142(A) and see if this would apply. The neutral from the transformer to the service main bonding jumper is a grounded conductor. In 250.142 it says the grounded conductor can only be used to ground non-current carrying parts only at the 3 locations listed. If the use of the grounded conductor does'nt fit any of the 3 items listed, then it would be a violation to use the grounded conductor in the manner you dscribe.
Rick
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First I would like to say I agree with the comment that you should check with your AHJ. Right or wrong, there is no guarantee your inspecor will agree with us.

Regarding 250.142, we aren't using the neutral to ground the metal parts of the enclosure, the ground wire still does that.

I don't really see any difference between using a transformer with a 3 pole switch, and using a generator with a 3 pole switch. This is fairly common (probably more common than using a 4 pole switch.)

The generator doesn't have to be considered a SDS, so why would the transformer. I uploaded a couple of diagrams I copied from a book (I think Smart$ still draws these better) that show the two choices you normally get for a generator.

Again, I don't really see any difference between a generator, and a transformer. With either one, your choices are:
1. Bond N-G at the gen or trans., call it an SDS, and use a 4 pole switch.
2. Don't bond N-G at the gen or trans, don't call it an SDS, and maintain a solid connection to the utility N-G bond with a 3 pole switch.


View attachment 3057
 
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Pardon by butting in again on this thread, but now I happen to notice and wanted to point out that it looks as though the grounding at the generator would not be required, but it is permitted under Section 250.54… (would this be correct ??) Equipment grounding conductors are still required...


… And now I have to question… is the midpoint delta connection even necessary at the generator?? Is it possible (are there issues) to just run the generator as a delta output 3-wire ?? I have provided another drawing to clarify my last question…


Again, pardon my intrusion here… I am just wanting to learn on this excellent opportunity…

mweaver
 
mweaver said:
Pardon by butting in again on this thread, but now I happen to notice and wanted to point out that it looks as though the grounding at the generator would not be required, but it is permitted under Section 250.54? (would this be correct ??) Equipment grounding conductors are still required...


? And now I have to question? is the midpoint delta connection even necessary at the generator?? Is it possible (are there issues) to just run the generator as a delta output 3-wire ?? I have provided another drawing to clarify my last question?


Again, pardon my intrusion here? I am just wanting to learn on this excellent opportunity?

mweaver
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You're not butting in, we are all here to learn, so feel free to ask away.

I think you are right about the extra ground electrode at the generator (although it might actually be required if the generator is outside and is considered a separate structure.)

I think the neutral connection to ground at the generator would probably be required per 250.20: Systems to be Grounded. Otherwise the generator windings, the high side of transformer, and the interconnecting wiring would all be an ungrounded system.

Steve
 
Steve66,

Thanks for assuring me on the butting in...



On your statement: "Otherwise the generator windings, the high side of transformer, and the interconnecting wiring would all be an ungrounded system. "

I guess I don't see an issue as to whether the generator is operated as a three wire ungrounded system, or a 4 wire grounded system...


However, if it were to be operated as a 3-wire delta system, then (technically) Section 250.21(B) kicks in and ground detectors would be required...

mweaver
 
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I hope no one is considered butting in, if so I am shamed.

My answer to you question would be that the midpoint of the delta connection is not required or necessary but a very good idea unless you had issues otherwise. 250.20 (B)(3) states “….. when the midpoint of one phase winding is used as a circuit conductor”. In our example we are only serving line to line load to the transformer primary.

250.21 would be a requirment.
 
RUWired said:
exactly and we are. and 250.142 are talking about system grounding.
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No we are not.

250.142 is talking about using the system grounded conductor as the means for equipment grounding in lieu of an EGC, i.e. using a neutral as an EGC. This is not the same as using a grounded service conductor as the means to ground a derived system.

RUWired said:
without using the grounded conductor in the manner you describe the transformer will not have its system grounded.
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Correct... but it is not without said conductor, and said conductor does effectively ground the derived system and in a compliant manner.

RUWired said:
you need the system bonding jumper for the transformer to work.your using the grounded conductor to tie the system to ground.
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Yes, I am. The requirement for a system bonding jumper is for Separately Derived Systems. But when a transformer (or generator, for that matter) achives it's source grounding by way of a solidly-connected service-system grounded conductor, the transformer (or generator) is rendered a derived system?but not a Separately Derived System?for it supplies service-system loads. Part of the definition of an SDS is that it serves other than service-system loads. In this case, it does not. In fact, using this wiring configuration makes the tranfsormer part of the service system.
 
Guys, my point to quoting 250.142 is a technical point.

I agree that the transformer is wired in Smart$'s drawing exactly like a non SDS generator and i agree we could call it a non seperately derived transformer.

Article 250.35 gives us permission to wire generators as non seperately derived systems. There is not a single article that gives us permission to wire transformers as non seperately derived systems.

Article 250.142 gives us permission to use the grounded conductor in the following manner...

A grounded circuit conductor shall be permitted to ground non?current-carrying metal parts of equipment, raceways, and other enclosures at any of the following locations:

(1) On the supply side or within the enclosure of the ac service-disconnecting means
(2) On the supply side or within the enclosure of the main disconnecting means for separate buildings as provided in 250.32(B)
(3) On the supply side or within the enclosure of the main disconnecting means or overcurrent devices of a separately derived system where permitted by 250.30(A)(1)

Since this transformer is not a SDS and it does not fit any of the 3 listed locations and is not a generator, the grounded conductor does not have permission to be used to "ground non?current-carrying metal parts of equipment, raceways, and other enclosures"
My technical point is untill permission is granted, this install is unsat.

Rick
 
One other point i could make that could actually be the same scenario is article 450.6 and 450.6(C). The secondary ties are very similar to the non SD transformer and the utilities transformer. The only difference is locations of equipment. My point for reference is 450.6(C).



(C) Grounding. Where the secondary tie system is grounded, each transformer secondary supplying the tie system shall be grounded in accordance with the requirements of 250.30 for separately derived systems.

Rick
 
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