Ground from Transformer to gear.

Merry Christmas
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LazyS

Member
Location
Dallas TX
Have 5 runs of 400 coming from pad mounted utility transformer running underground 200 feet to switchgear. 208 with neutral. Utility company does not want my grounds entering their transformer. Do I originate my ground at the first means of disconnect(the gear) or do I have to pull a ground with the service? By the way it is PVC and Rigid.
 

iwire

Moderator
Staff member
Location
Massachusetts
LazyS, let me ask this.

Does an EGC run from your home all the way back to the utility transformer?


Nope.:smile:

Nothing changes with this much larger service, all you should have between the utility transformer and the new service disconnect are the hots and neutrals.

Your EGC must originate at the service disconnecting means enclosure.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
First, welcome to the Forum.
Secondly, you will find some of us are picky b******. "Ground" ?????
Grounded or grounding .. makes a big difference :smile:
Most commonly, your grounding and grounding electrode conductors will
originate at your gear. Only your groundED conductor will originate at the pad with your phase conductors. With the PVC/Rigid mix you will need to be sure your metallic conduits are bonded per 250.92

(sorry bob, I was posting on top of you..good explaination on your part -as always)
 

ohmhead

Senior Member
Location
ORLANDO FLA
Well if i think what your saying is if there parrelled runs NO ! If its a single RUN NO ! From the power company transformer to the first disconnect no ground wire is done ever .



The grounding conductor is not needed from the power companys transformer we only run hots and the neutrals = grounded conductor the grounding conductor is done at your service disconnect .

Be safe
 

iwire

Moderator
Staff member
Location
Massachusetts
Did a job once where the engineer made us pull grounds in.

Yes, common to see it specified on prints, still can not connect it.

If you do run an EGC between the utility transformer and the service disconnect then land it at both ends what you have is not an EGC but just a parallel MGN (Multi Grounded Neutral)
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Bob, Hypothetical... what if, in Flex's situation, you didn't bond the grounded at the service. with the grounding brought from the transformer to the grounding terminal, would you have a violation ?
 

iwire

Moderator
Staff member
Location
Massachusetts
Bob, Hypothetical... what if, in Flex's situation, you didn't bond the grounded at the service. with the grounding brought from the transformer to the grounding terminal, would you have a violation ?

I do not see a safety issue with your hypothetical, it would be just like all the SDS I install.

However I think you would have a direct NEC violation of 250.24(B).

'within the enclosure for each service disconnect'
 

iwire

Moderator
Staff member
Location
Massachusetts
guess that makes sense from an "accessibility" standpoint.

Total guess here on my part but I assume it as a lot to do with control. If the power company swaps the transformer the NEC would have no control over what they do and the POCO might not reconnect the EGC as they do not normally see one on their end.

But that is just a guess. :smile:
 

roger

Moderator
Staff member
Location
Fl
Occupation
Electrician
You run rigid (or any metallic raceway) and you take a EGC to the transformer, you run PVC and parallel paths are not an issue.

Brian, this can be solved by bonding the metalic conduit only at the service end and letting it float in the transformer.

Roger
 

brian john

Senior Member
Location
Leesburg, VA
Brian, this can be solved by bonding the metalic conduit only at the service end and letting it float in the transformer.

Roger

True BUT 99% of the installs I see are either intentionally bonded or accidently as in poured slab with conduits imbedded in the concrete tied to re-bar and transformer mounted to the slab.

If it is a metallic raceway such as a service trough very hard to avoid.
 

iwire

Moderator
Staff member
Location
Massachusetts
True BUT 99% of the installs I see are either intentionally bonded or accidental as in poured slab with conduits imbedded in the concrete tied to re-bar and transformer mounted to the slab.

If it is a metallic raceway such as a service trough very hard to avoid.

Strictly speaking if a metal raceway ends up in parallel with the neutral between the utility transformer and the service disconnect you do not have an NEC violation and it happens at every house with RMC between the meter socket and the service disconnect.

I personally have never run, or seen RMC all the way from a service disconnect to the utility transformer.

What I do see is RMC 90s under the service disconnect changing to PVC for the straight run and then turning up at the transformer with RMC 90s again.

Of course we have to bond the RMC 90s at each end which will give the appearance of metal conduits in parallel with the neutral but that really are not. In this case lifting the bond between the RMC and the transformer would be a violation and be dangerous.
 

cadpoint

Senior Member
Location
Durham, NC
You run rigid (or any metallic raceway) and you take a EGC to the transformer, you run PVC and parallel paths are not an issue.

Brian, this can be solved by bonding the metalic conduit only at the service end and letting it float in the transformer.

Roger

True BUT 99% of the installs I see are either intentionally bonded or accidently as in poured slab with conduits imbedded in the concrete tied to re-bar and transformer mounted to the slab.

If it is a metallic raceway such as a service trough very hard to avoid.

I think I'm facing that right now. but a little bit different

I have a "U" structure of conduits the stacks are rigid between PVC, the inspector has already told me to bond the ends of each stack, well ok this is the Line side from the transformer it does not drop out of the bottom of the transformer.

So based on this Float statement on the Transformer stack I need to apply bonding bushings and let the line side of the Ground wire back to the MDP ground the stack, I guestioned all this with my Engineer (of record), he's got to talk it out with POCO because my questions got them to a thinking...

So, heres the newest plan, I supply a grounding triad for the building and it will run up to the Transformer vault thats it.
I install a second PVC conduit from the triad to the MDP, that's it, for now.
there calling back Monday...

It's already a Hot summer :D
 

brian john

Senior Member
Location
Leesburg, VA
Strictly speaking if a metal raceway ends up in parallel with the neutral between the utility transformer and the service disconnect you do not have an NEC violation and it happens at every house with RMC between the meter socket and the service disconnect.

I personally have never run, or seen RMC all the way from a service disconnect to the utility transformer.

What I do see is RMC 90s under the service disconnect changing to PVC for the straight run and then turning up at the transformer with RMC 90s again.

Of course we have to bond the RMC 90s at each end which will give the appearance of metal conduits in parallel with the neutral but that really are not. In this case lifting the bond between the RMC and the transformer would be a violation and be dangerous.

No violation, but it can result in neutral ground current issues, especially with services with high neutral current. Sharing a portion of that current on the EGC.
 
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