Transformer grounding

[david]

This is legal take a look at 250.30 A7 exception No. 2 you must bond your electrode to the conduit if it is metal.

Sorry I thought you where saying that he could use 250.30 (A)(7) (2) exception 2 my mistake
Please pardon.

 

[shaw0486]

well he may be able too. Im not sure i understand his sinario though

 

[arnettda]

[QUOTE=shaw0486;1138859]well he may be able too. Im not sure i understand his sinario though[/QUOTE]

My confusion is really seeing the difference in my equipment ground for the primary side of the transformer and my grounding electrode conductor since they both are comming from the same ground buss . The more I read the more I am understanding.

 

[augie47]

Is there a conductor from your ground buss to building steel ?

 

[david]

Ok the ground in the primary would hit the \frame than go to xo keep it continuous. the ground from the secondary would just hit the frame.

Am I confused in what you are saying because it sounds to me like you are telling him that the primary feeders equipment ground is to connect to the frame of the transformer for primary side fault clearing then go continuous (without splice) to the secondary (derived neutrals) xo.

Do not bond the primary side equipment ground to the secondary side xo.

 

[arnettda]

Is there a conductor from your ground buss to building steel ?

Yes there is.

 

[augie47]

If your primary is in metallic conduit all the way to the transformer that conduit would serve as your primary grounding conductor.
If the buss (and associated wiring) meet the requirement of 250.30(A)(3), I see no problem with your secondary bonding.
I see no need for the added primary grounding conductor to the buss and it would, IMHO, be a violation of 300.3

 

[david]

[/B]

My two seperate grounds would go the the frame of the transformer. And I would only have one wire that would go from frame to the neutral lug of transformer?

Is this different than bringing all wires to the big neutral bar of transformer and then bringing one wire down to bond the frame of transformer?

yes there is a difference.
When the code talks about grounding or bonding the (neutral) it is talking about a direct connection between the two. Pretend you?re the neutral and I am the grounding electrode conductor when we shake hands we are bonded. The other approved way would be through a main bonding jumper when there is no direct connection.

You as the grounded (neutral) conductor would grab one end of the bonding conductor and I as the grounding electrode conductor would be connected to a two barrel connector or an approved bus bar to have a direct connection to the main bonding jumper

You cannot rely on the transformer?s metal encloser to make this bond to the (Neutral) grounded conductor.

 

[david]

250.30 (A) (5)
(5) Installation. The installation of all grounding electrode conductors shall comply with 250.64(A), (B), (C), and (E).

250.64 C) Continuous. Grounding electrode conductor(s) shall be installed in one continuous length without a splice or joint except as permitted in (1) and (2):


The grounding electrode conductor has to be continuous from your secondary systems derived neutral to the grounding electrode.
Unless permitted in (1) and (2)

I you are trying to use this primary system equipment grounding bar as a connection point between the secondary neutral and the grounding electrode this would violate 250.64

 

[david]

I hope I can make this simple enough. I have a primary disconect for a transformer. Whoes equipment ground comes from a central grounding point which is a copper buss. /////////////// Now the grounding conductor I run to building steel I want to run back to this copper buss! As building steel is not really accessable

I hope you still are not confused. You have to find an accessible grounding electrode in an area as close to your transformer as you can. You must run the grounding electrode conductor un-spliced (With a couple of exceptions) from your transformer grounded conductor to the grounding electrode.

Once you established the point of bonding in your case, the transformer all bonding and grounding of the transformers derived neutral has to happen at that same location (one eception)

You cannot run your grounding electrode conductor to this central copper equipment grounding bar for a couple of reasons

1. This would be a splice of the grounding electrode conductor
2. The grounding electrode conductor has to be sized table 250.66 based on the secondary ungrounded phase conductors
3. All bonding on the secondary derived system has to happen at he same location. Their is one exception to this no other metallic paths between the secondary system and the first disconnect but I don?t think we should confuse this any further