Xfmr grounding

[ashtrak]

Were setting a 480/120/208 xfmr for a small deli, 45kva xfmr is fed from a 480 volt 80 amp breaker (all three phase), secondary is three phase 125 amp breaker.Primary wire is #2 secondary is #1/0 thhn.Surrounding structure is all concrete (no steel) Electric room has a ground grid but it would take drilling two feet of concrete to make it an excessable place to ground( it's about sixty feet away).There is a small bathroom with cold water (copper), of course I dont know if its a good path of copper back to the Main valve (continuity?).

My question is what alternative do I have for grounding my xfmr neautral, Would the bathroom cold water suffice, or should I plan on drilling the two feet of concrete to reach the building ground.

I am on grade so a ground rod would be a possibilty, however I'd rather not drill the floor due to high voltage feeders,cathodic protection and or plumbing issues...

I've set seperatly derived systems many times before, but never had such a hard time finding a building ground.

Thanks

 

[dana1028]

I am on grade so a ground rod would be a possibilty, Thanks

Correct me if I am misunderstanding the code - even if you were to drive a rod, you would still have to make a connection to the buildings electrode system. That is, you can't 'float' a separate electrode on the premises.

 

[bgeorge]

Also, that would apply to having "no parallell paths to ground" I also agree that you have to get to the building elctrode sytem.

 

[Smart $]

My question is what alternative do I have for grounding my xfmr neautral

Run a dual-pupose GEC/EGC with the feeder, sized per 250.66.

 

[David Nelson]

Transformer Bonding

Transformer Bonding

You definitely have to get back to the main GEC. You cannot establish a separate connection to earth. The conductor should be sized according to 250.66

 

[luckyshadow]

Follow 250.30
specifically 250.30 (A)(7).
Building steel or Water

 

[RUWired]

Run a dual-pupose GEC/EGC with the feeder, sized per 250.66.

Along with a larger conductor per 250.66, you would be required to bond all the raceways and enclosures to the transformer per 250.64E, you would be required to make the dual purpose GEC/EGC continuious to the existing GES or GEC via an irreversible connection per 250.64C, and you would still be required to bond the copper water line in the area if you could not determine if there is an existing jumper made with the existing GES at the service per 250.104D exception no. 1. Article 250.30A7 requires the GEC to be made as near as possible and in the same area as well.

I'm just pointing out that just running it as a dual purpose conductor has some additional requirements.

Rick

 

[dana1028]

Along with a larger conductor per 250.66, you would be required to bond all the raceways and enclosures to the transformer per 250.64E, you would be required to make the dual purpose GEC/EGC continuious to the existing GES or GEC via an irreversible connection per 250.64C,

I could have sworn that Don R had indicated this constitutes a technical violation of the code.

RE: "and you would still be required to bond the copper water line in the area if you could not determine if there is an existing jumper made with the existing GES at the service per 250.104D exception no. 1."

250.104(D) requires the bonding of the water piping system for the XO - regardless of whether or not the building electrical system has such a connection. Exception 1 says you don't have to make this water bond a second time [if you have already made such a connection for the transformer electrode system].

 

[Pierre C Belarge]

If there is no structural steel that qualifies as an electrode in the vicinity, you will be required to go back to the water no further than 5ft from entry to the building. 250.30(A)(7) (of course if there is a water electrode to begin with)

 

[Jesse7623]

Correct me if I am misunderstanding the code - even if you were to drive a rod, you would still have to make a connection to the buildings electrode system. That is, you can't 'float' a separate electrode on the premises.

Yes you have to go back to the GEC with a ground wire sized to 250.66

 

[don_resqcapt19]

Dana,
I have said that you could use a single conductor for both the primary EGC and the secondary GEC as long as you comply with all of the rules for both as Rick stated in post #7. There has been a proposal that was approved at the ROP meetings to prohibit this.

 

[dana1028]

Dana, There has been a proposal that was approved at the ROP meetings to prohibit this.

Just making sure I understand - for now a dual purpose conductor is permitted; however this may change with the next code cycle.

 

[don_resqcapt19]

Just making sure I understand - for now a dual purpose conductor is permitted; however this may change with the next code cycle.

There are others who say it is not permitted, but as long as you comply with all of the rules for both conductors, I see nothing in the current code that says you can't install a dual purpose conductor.