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Equipment ground required between transformers?

Equipment ground required between transformers?

Equipment ground required between transformers?

(OP)
I have a case where the utility feeds a customer owned 240:480 transformer, then there is about a 2000 foot run to a 480:120/240 transformer to a panel that feeds the load circuits. I understand this forms a SDS at the load end, but is an EGC required to be also run between the two transformers? I am finding conflicting information on this. Thanks
 

RE: Equipment ground required between transformers?

Both transformers are SDS.  If the secondary of the first transformer is not grounded, 250.32(C)(1) requires an equipment grounding conductor between the two transformers.  If the secondary is grounded, then 250.32(B)(1) requires an EGC.  Code references are from the 2011 code.

RE: Equipment ground required between transformers?

(OP)
Thank you for your reply -- but I'm more confused. What exactly would the secondary be grounded to? There is no netural, its just 480V hot legs off the secondary.

Also, you advise that (C)(1) requires an ECG between the transformers if not grounded, but then you say that (B)(1) requires an EGC if the secondary IS grounded.

RE: Equipment ground required between transformers?

The code requires an EGC to be run with almost all circuits.  It the case of ungrounded circuits, it is to provide a fault clearing path in the event of two ground faults on differnt phases.  
As far as what it would be connected to at the secondary of the transformer, the code requirements for a grounding electrode at an ungrounded SDS are the same as those for a grounded one.  See 250.30(A) for grounded systems and 250.30(B) for ungrounded systems.

RE: Equipment ground required between transformers?

(OP)
Thanks very much.

RE: Equipment ground required between transformers?

The Canadian code does not always require an equipment grounding conductor to be run to a sub-service in a separate building. At 2000 feet, is this a very large building or a second building? Is there a similar provision in the NEC?
 

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Equipment ground required between transformers?

Bill,
In the 2005 and earlier NEC you were not required to run an EGC to the second building in all cases.  Where an EGC was not required you would bond the grounded conductor to a grounding electrode and the second building and the EGCs for that building would originate there.   Starting with the 2008 NEC, you are required to run an EGC to the second building and connect that EGC to a grounding electrode at the second building.  The grounded conductor cannot be connected to the EGC or grounding electrode at the second building under the current codes.  

Note, I had assumed we were talking about two structures, but in this case even if both of the transformers are in a common building the rules in the NEC would be almost identical and result in the same installation.  That is a grounding electrode would be required at both transformers and an EGC would be required to be installed between the transformers.   

RE: Equipment ground required between transformers?

Thank you for the update. I'll have to check the current Canadian code.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Equipment ground required between transformers?

(OP)
The structure 2000 feet away is an equipment cabinet, not a building but I believe it still counts as a "structure". This statement is a little confusing in my case though.. " The grounded conductor cannot be connected to the EGC or grounding electrode at the second building under the current codes".  If I am coming off of a 480 to 240/120 transformer at the load end, would I not be required to bond the new neutral to ground at the transformer OR panel as this is a SDS?
 

RE: Equipment ground required between transformers?

The statement in the code that says that the grounded conductor cannot be connected to the EGC or to a grounding electrode at the second building or structure applies to a grounded conductor that originated at the first building or structure.   
The secondary of your transformer at the second structure is a SDS that is required to be a grounded system by the rule in 250.20(B).  This requires the connection of the grounded conductor to a grounding electrode.

RE: Equipment ground required between transformers?

(OP)
OK, That makes more sense. Thanks

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