Ground Wire From 3 Phase Pad Mounted Utility Transformer

[hurk27]

When you have an SDS you will have a service disconnect ahead of it even if it is a MV switch, the disconnect at the building is now an article 225 issue as well as the wiring between the SDS and the building disconnect required in 225, the rules of 225 now apply and grounding and bonding is done like any out building. 230 is about utility service up to the point of the utility service disconnect after this it is a 225 issue if the service point is not at the building.

 

[iwire]

Read the second paragraph 4th sentence in red in post #34. I specifically mentioned services may have objectionable current while being code compliant. You are just repeating what I already knew and mentioned prior. And yahh, pipes will pass current outside of the structure. But that's beyond the SDS.

So we both agree that neutral current flows on many metal raceways and pipes etc? Is it objectionable current? Not in my opinion and with no definition available no one can say.

But, again, what if your main service is at the medium voltage level?

You would have to install a medium voltage service disconnecting means. As a few of our customers have done.

And you haven't answered why the Mike Holt graphic allows for a 4 wire feeder when the utility is out of the picture.

I was not aware I was required to answer all questions. I did not look into that end of this discussion at all. It did not interest me and I am not going to comment on it blindly.

The code section you posted does not prohibit SDS from a pad mount (only equipment when considered a service).

The code section I posted directly prohibits a power transformer to be installed on the supply side of the service disconnecting means.

I saw no where 'shall be 3 and 4 wire over 4 and 5 wire or shall not be considered SDC in any case'

And you wont find that, you don't need to find that. The fact that the service disconnect is on the load side of the padmount in discussion means it cannot be wired as, or called an SDS under the NEC.

 

[kwired]

But, again, what if your main service is at the medium voltage level? And you haven't answered why the Mike Holt graphic allows for a 4 wire feeder when the utility is out of the picture.


The code section you posted does not prohibit SDS from a pad mount (only equipment when considered a service). I saw no where 'shall be 3 and 4 wire over 4 and 5 wire or shall not be considered SDC in any case'

Others have hit on the fact that if service voltage is medium voltage - you still need a service disconnecting means- it will just have to be one rated for the applied voltage.

As far as 3 wire, 4 wire, 5 wire.... If the load supplied by the service utilizes the neutral you will need both neutral and equipment grounding conductor run from that service disconnecting means. If the medium voltage load is just a transformer - say with a delta primary and doesn't utilize a neutral then all you need is to supply it with the three ungrounded conductors and an equipment grounding conductor.

You could do exactly same thing with a 480 volt service that supplies nothing but a 208/120 transformer - with only real difference being the use of 600 volt or less equipment and conductors instead of medium volt equipment.

 

[mbrooke]

So we both agree that neutral current flows on many metal raceways and pipes etc? Is it objectionable current? Not in my opinion and with no definition available no one can say.

Only at the service. And yes I get its 100% code complaint. Objectionable is relative here. And as I said if its that great of a concern just use plastic conduit.


You would have to install a medium voltage service disconnecting means. As a few of our customers have done.

I get that.


I was not aware I was required to answer all questions. I did not look into that end of this discussion at all. It did not interest me and I am not going to comment on it blindly.

Wait you say you weren't going to comment blindly but didn't read the whole thing.:blink: A bit contradictory?


The code section I posted directly prohibits a power transformer to be installed on the supply side of the service disconnecting means.

The transformer feeds the disconnect. It doesn't tap off of it.

And you wont find that, you don't need to find that. The fact that the service disconnect is on the load side of the padmount in discussion means it cannot be wired as, or called an SDS under the NEC.

What ever its called, for the sake of the argument I will take Mike Holts explanation.

 

[hurk27]

What ever its called, for the sake of the argument I will take Mike Holts explanation.

First the video is about taps in 240.21(C), a little later in the video he explains that because the transformer is customer own that the conductors feeding the disconnect are in fact feeders not service conductors, the disconnect on the building is a 225.31 required disconnect not a 230.70 disconnect, thus 250.32(B) will require a separate EGC as you can not use the neutral for grounding after the service disconnect (I think before 2008 it was allowed via the wording of 250.32(B)(2) 2008 and after it only is allowed for existing.
Again the disconnect in the MH graphic you posted earlier is not a service disconnect it is a 225 disconnect required in 225.31, what MH does not explain in the video is there is a service point/disconnect ahead of the transformer in the graphic.

 

[mbrooke]

First the video is about taps in 240.21(C), a little later in the video he explains that because the transformer is customer own that the conductors feeding the disconnect are in fact feeders not service conductors, the disconnect on the building is a 225.31 required disconnect not a 230.70 disconnect, thus 250.32(B) will require a separate EGC as you can not use the neutral for grounding after the service disconnect (I think before 2008 it was allowed via the wording of 250.32(B)(2) 2008 and after it only is allowed for existing.
Again the disconnect in the MH graphic you posted earlier is not a service disconnect it is a 225 disconnect required in 225.31, what MH does not explain in the video is there is a service point/disconnect ahead of the transformer in the graphic.

That's the explanation I was looking for. Makes perfect sense now!

I was using the wrong terms. Sorry about the confusion:ashamed1: