XO Transformer connection

[rookie4now]

I have a question about the X0 connection here. The copper strap is bonding X0 to the chassis. Is the current connection correct. The inspector said the the Ground needs to land on the X0 terminal. If that's the case I suppose I would need a double lug to land the ground and the neutral on the X0 terminal. He also said something that seemed odd to me. He essentially said that I needed to demonstrate that the building steel that we used to ground the transformer was physically tied to the service. I do very little work with transformers but I thought the building structural steel was a very common and accepted means of grounding.

Also, if anyone can recommend a good link for learning more about transformers I'd like to increase my understanding.

Thanks

 

[iwire]

The copper strap is bonding X0 to the chassis.

No, that copper strap bonds the transformer frame to the transformer enclosure. That needs to be done because the transformers frame sits on rubber isolators to help keep them quiet.

It is up to the installer to bond XO when required .... and it is.









Why are both the incoming and outgoing conductors the same colors?

Where are the equipment grounding conductors and equipment bonding jumpers?

If it was my transformer you would see a three barrel lug on the neutral and at least a three barrel lug on the transformer enclosure. (Note, the 2014 requires a grounding bar for this now)

Please tell us more about this transformers voltages, usage and where the line and load side run to.

 

[augie47]

The copper strap you see is not bonding XO to the transformer.
You do need a XO to ground(ing) connection.

 

[rookie4now]

Thanks for the input. it is a 480 delta to 480 wye. If I'm understanding this correctly then, we could take the GEC which is currently terminated at the chassis and instead of terminating it there, pull it through the lug on the chassis and terminate it along with the load side neutral to a double lug on the X0. Correct? the load side is a 3P panel with 3 3P 20a circuits for some special equipment that is being installed by others.

Any thought on the building structural steel question?

 

[domnic]

XO

XO

Is the primary wiring bonded to the transformer housing?

 

[infinity]

Thanks for the input. it is a 480 delta to 480 wye. If I'm understanding this correctly then, we could take the GEC which is currently terminated at the chassis and instead of terminating it there, pull it through the lug on the chassis and terminate it along with the load side neutral to a double lug on the X0. Correct? the load side is a 3P panel with 3 3P 20a circuits for some special equipment that is being installed by others.

Any thought on the building structural steel question?

If the steel is an electrode it must be part of the GES.

 

[augie47]

The metal frame of the building should be bonded to the service either as a grounding electrode (if applicable) per 250.52(A)(2) or bonded per 250.104(C_ if it's not an electrode. Likewise the building steel could serve as an electrode for your transformer per 250.30(A)(7).
I have no idea why the inspector wants the verification on the service but can see why he would be interested in the grounding electrode for the transformer which does not appear to be connected in the picture.

 

[GoldDigger]

FWIW the building steel, via its connection to the concrete, may be a ground electrode whether bonded to the GES or not. But unless it is tied by wire or other metallic bond to the GES (which we can assume is bonded to the POCO neutral) we and he cannot be sure that there is an adequate fault clearing path for a fault in the transformer primary.