2017 transformer grounding- separetly derived

[mbrooke]

Ok, so I hear a lot of changes took place in article 250. One of them being that a separately derived transformer (such as a 480 delta-120/208Y) requires that its grounding electrode conductor be taken back to the main service GEC rather than bonded to the nearest steel beam. If this is true, my question is why? What was the reasoning behind eliminating what was sound rule?

 

[Smart $]

Committee statement on first revision is:

These revisions better describe a grounding electrode and include the conductors that are suitable to extend the grounding electrode connection.

The revisions to this section recognize the water pipe and the structural metal frame as covered in 250.68(C) that are being used are not grounding electrodes but rather are conductors extending the grounding electrode connection.


The revised text allowed exception No. 1 to be deleted as those options are covered by the referenced sections. Editorial changes were made to 250.30(A)(4), former Exception No. 2 to make it technically correct.

Submitter is CMP 5.

Note the change does not prohibit your from bonding your GEC to the water pipe or structural steel. 250.30(A)(5) says you can run your GEC per 250.30(A)(4) or as permitted in 250.68(C)... which is where Code says you can use the water pipe or structural steel to extend the connection to the building or structure GES. Note the GEC to the service must be sized at least as large as the minimum required GEC for the SDS. I mention this because it could present a problem where most or all of the service current goes to a step-down transformer.

 

[mbrooke]

Committee statement on first revision is:

Submitter is CMP 5.

Note the change does not prohibit your from bonding your GEC to the water pipe or structural steel. 250.30(A)(5) says you can run your GEC per 250.30(A)(4) or as permitted in 250.68(C)... which is where Code says you can use the water pipe or structural steel to extend the connection to the building or structure GES. Note the GEC to the service must be sized at least as large as the minimum required GEC for the SDS. I mention this because it could present a problem where most or all of the service current goes to a step-down transformer.

So I can use a steel column provided its a known electrical connection (continuity) to the service electrodes?

 

[Sahib]

a separately derived transformer (such as a 480 delta-120/208Y) requires that its grounding electrode conductor be taken back to the main service GEC rather than bonded to the nearest steel beam. If this is true, my question is why? What was the reasoning behind eliminating what was sound rule?

So I can use a steel column provided its a known electrical connection (continuity) to the service electrodes?

May be for providing single ground reference.

 

[iwire]

So I can use a steel column provided its a known electrical connection (continuity) to the service electrodes?

Yes, you can use the steel frame of the building as a conductor of the grounding electrode system.

 

[mbrooke]

Yes, you can use the steel frame of the building as a conductor of the grounding electrode system.

Under the 2017, correct?

 

[Smart $]

Under the 2017, correct?

Under 2014 even. Perhaps many earlier editions, but I haven't verified.

 

[iwire]

Under the 2017, correct?

IMO yes and before as smart mentioned.

A job I did in the 90s I used that to save about a 300' run of 3/0 copper and the EMT raceway it would have been in. The service was about 300' from the metal water service.