transformer grounding and bonding

[petersonra]

just curious what you guys do.

I am writing some specs for doing various things, and it occurred to me that a consistent manner of grounding and bonding of SDS transformers might be useful.

I am not sure, but it appears that at least some of the xfmrs we are using have some kind of a ground stud that comes with it attached to the enclosure. if it did not come with one, a machine screw could be added.

What I am thinking of doing is having the neutral, GEC, and EGC all tie to that stud, which would also become a de facto SBJ.

I can't see any real issues with this, but I thought I might put it out there for comments.

Not sure how to handle xfmrs with no enclosure. They might have to be handled a little differently.

I am kind of thinking I might add a lug near the xfmr for the GEC to land on. Having said that I know the chances of anyone actually bringing in a GEC approaches zero.

 

[augie47]

Over the years it has become SOP with most of the contractors in this area to mount a ground bar to the transformer case and terminate a system bonding jumper, an equipment bonding jumper and a grounding electrode conductor there. Often, when there is a factory stud they will incorporate that to fasten the ground bar.
It's amazing how many electricians seem to be confused about grounding SDS and a "standard method", no matter what it is, is a great idea for many for most of the shops. Kudos on your effort.

 

[GalwayElectric]

Aug when you bond the sbj, ebj, and gec at the transformer you need to keep the gec and neutral separate at the first disconnect/panel downstream correct?

 

[don_resqcapt19]

Aug when you bond the sbj, ebj, and gec at the transformer you need to keep the gec and neutral separate at the first disconnect/panel downstream correct?

In that case there would not be a GEC at the disconnect. You would run the phase conductors, the grounded conductor and a supply side bonding jumper between the transformer and the disconnect. The bonding jumper would land on the equipment grounding terminal bar and the grounded conductor would land on the neutral bar. There would be no connection between the two at the disconnect.

 

[GalwayElectric]

Yep thanks Don

 

[petersonra]

Over the years it has become SOP with most of the contractors in this area to mount a ground bar to the transformer case and terminate a system bonding jumper, an equipment bonding jumper and a grounding electrode conductor there. Often, when there is a factory stud they will incorporate that to fasten the ground bar.
It's amazing how many electricians seem to be confused about grounding SDS and a "standard method", no matter what it is, is a great idea for many for most of the shops. Kudos on your effort.

what kind of ground bar are they using?

I have had this conversation a couple of times with various people who should know and have come to the conclusion that a ground bar is required to have an SCCR suitable for the potential SCC that might be present. Most of the common ground bars used do not have a SCCR.

What I had in mind was ring type lugs all connected together at the stud. The neutral wire(s) from the xfmr, the GEC, and the EGC. This will be a strange looking arrangement because what I am thinking of doing is running the GEC to a lug on the panel where it would have another ring that connects to the lug via the mounting bolt. The EGC would go to the same place. The lug terminal would be for the external GEC connection.