Transformer Secondary grounding and bonding

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Electriman

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Greetings,

I am hoping to get some advice of how to ground the secondary Delta-Wye transformer. Does NEC allow to have two neutral to ground connection one at the transformer and one at the switchboard?

Thank you in advance.
 
No, you could install the SBJ at either location but not both. The GEC would land at the location of the SBJ. We always install the SBJ at the transformer.
 
Electriman said:
Greetings,

I am hoping to get some advice of how to ground the secondary Delta-Wye transformer. Does NEC allow to have two neutral to ground connection one at the transformer and one at the switchboard?

Thank you in advance.
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Not for a typical transformer installation. See 250.30(A)(1). It states "single point". There is an exception for outdoor transformers.
 
infinity said:
No, you could install the SBJ at either location but not both. The GEC would land at the location of the SBJ. We always install the SBJ at the transformer.
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It seems that utility transformers are exception, am I right? What is NEC recommended place for neutral to ground connection, transformer or panel?
 
No recommendation. For single phase, If the SBJ is at the panel, three wires to the xfmr. White wire is for neutral and EGC. If the SBJ is at the transformer, its 4 wires, 2 hot, neutral and EGC. Neutral sizing may be different in each case
I connected a lot of smallish 5 KVA transformers for lighting, 480x120/240 it was easier to use the SBJ green screw in the panel, as the transformers have wire leads.
 
tom baker said:
For single phase, If the SBJ is at the panel, three wires to the xfmr. White wire is for neutral and EGC. If the SBJ is at the transformer, its 4 wires, 2 hot, neutral and EGC. Neutral sizing may be different in each case
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Well, this is 3ph, so the numbers would be four and five, respectively, but the idea is correct. (y)

If you bond in the transformer, the feeder needs a separate EGC and the panel is wired as a sub-panel.

If you bond in the panel, the feeder does not need a separate EGC, and the panel is wired as a service.
 
LarryFine said:
Well, this is 3ph, so the numbers would be four and five, respectively, but the idea is correct. (y)

If you bond in the transformer, the feeder needs a separate EGC and the panel is wired as a sub-panel.installed per

If you bond in the panel, the feeder does not need a separate EGC, and the panel is wired as a service.
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It may not be called an EGC from transformer to service panel, but wouldn’t a supply side bonding jumper have to be installed per 250.30(A)(2)?
 
Electriman said:
It seems that utility transformers are exception, am I right? What is NEC recommended place for neutral to ground connection, transformer or panel?
Click to expand...
Yes, utility transformers are different and they are bonded to earth at both the transformer and the service equipment.
For separately derived systems, the code does not give any recommenation as to the location of the neutral to ground connection. It just says it can be only at one of those locations. My determination is based only on the length of the required GEC. I place the system bonding jumper at the location that requires the least amount of conductor length from the SBJ and the grounding electrode. That is the only variable, as everything else is the same between the SDS and the first means of disconnect.
 
Greentagger said:
It may not be called an EGC from transformer to service panel, but wouldn’t a supply side bonding jumper have to be installed per 250.30(A)(2)?
Click to expand...
A supply side bonding jumper is always required between the transformer and the first means of disconnect, but it is not required to be of the wire type. Non-flexible metallic conduit is permitted to serve as the required supply side bonding jumper.
 
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