Transformer grounding

[curious23]

What is the correct thing to do in the following scenario. Installing a 15kva Delta 480 3 phase pri. To a wye 400 3 phase sec. The Transformer will be feed from a 277/480 Load center. The building has wood post frame, so I can not cad welding the ground to the building structure. Do I install a ground rod for the grounding electrode of the secondary side? Or would that not be correct?

 

[augie47]

Covered by 250.30...
Basically:
(4) Grounding Electrode. The building or structure grounding electrode system shall be used as the grounding electrode for the separately derived system

In addition you need to bond water piping & steel per 250.104(D)

 

[infinity]

As Augie stated you need to connect the GEC to the system GES. Pounding in a ground rod and connecting to it would not be code compliant.

 

[curious23]

If I pulled a ground wire from the 277/480 panel to the Transformer that would be enough? Without installing g a ground rod?

 

[LarryFine]

Welcome to the forum.

If the structure already has an electrode system, tie into it.

 

[bwat]

I believe the rules are relatively stringent, but isn't there a code section that allows EGC and GEC to be the same wire? Perhaps specifically with SDS? I quickly poked around trying to find the reference but came up with nothing.

Edit: Found it. Exception under 250.121

 

[curious23]

If I connected an equipment grounding conductor to the bonding terminal of the transformer. The new ground rod would be considered an Auxiliary Grounding electrode. 250.54. Would this make it code compliant?

 

[infinity]

If I connected an equipment grounding conductor to the bonding terminal of the transformer. The new ground rod would be considered an Auxiliary Grounding electrode. 250.54. Would this make it code compliant?

Where would the other end of the EGC be connected?

 

[curious23]

Where would the other end of the EGC be connected?

The xo tap on the secondary. The equipment Grounding conductor is coming from the existing building grounding system.

 

[curious23]

The xo tap on the secondary. The equipment Grounding conductor is coming from the existing building grounding system.

the xo tap , is connected with the equipment ground and the Auxiliary gec

 

[infinity]

The xo tap on the secondary. The equipment Grounding conductor is coming from the existing building grounding system.

The EGC for the transformer is connected directly to the building GES?

 

[curious23]

The EGC for the transformer is connected directly to the building GES?

yes

 

[infinity]

yes

How?

 

[curious23]

How?

I would run 3 current carrying conductors with an equipment ground in conduit, from the 277/480 Load center to the transformer. I would connect the equipment grounding conductor to the ground terminal installed at the transformer. From the xo tap on the secondary, I would connect a wire to the ground terminal in the transformer, then I would run a grounding electrode conductor to a 10'x 3/4" copper ground rod installed about 15' outside of the building.

 

[curious23]

I would run 3 current carrying conductors with an equipment ground in conduit, from the 277/480 Load center to the transformer. I would connect the equipment grounding conductor to the ground terminal installed at the transformer. From the xo tap on the secondary, I would connect a wire to the ground terminal in the transformer, then I would run a grounding electrode conductor to a 10'x 3/4" copper ground rod installed about 15' outside of the building.

Remember the Building is wood post frame. So, I can not use the metal structure of the building for GEC. Also, the closest metal water line is 200' away.

 

[infinity]

Can you explain further how you would comply with all of the requirements to use the EGC as a GEC? The additional ground rod is not relevant to that requirement.

250.121 Restricted Use of Equipment Grounding Conductors.
250.121(A) Grounding Electrode Conductor.
An equipment grounding conductor shall not be used as a grounding electrode conductor.
Exception: A wire-type equipment grounding conductor installed in compliance with 250.6(A) and the applicable requirements for both the equipment grounding conductor and the grounding electrode conductor in
Parts II, III, and VI of this article shall be permitted to serve as both an equipment grounding conductor and a grounding electrode conductor.

 

[curious23]

I thought 250.121 in some Instances allows a Egc to be used as a GEC? I think that applies in this instance. Maybe I am incorrect in thinking that.

 

[augie47]

250.30(A)(4) pretty much limits you to connect to the building GES.
IMO your best bet would be to use the exception in 250.121 but you need to assure your EGC was sized for the grounding electrode conductor and installed per Part II of Art 250 including 250.64(E).
Is this the only transformer on the premises ?

 

[curious23]

No, there are more. This transformer is for a single piece of equipment. And thank you

 

[augie47]

Since you have multiple transformers you might look at 250.30(A)(6) "multiple systems".
Common approach in buildings with multiple transformers and no steel framing.