Supply side bonding jumper

[mshields]

I've got a campus distribution system at a hospital where the service to the facility is 13.8kV. From the service switchgear (S&C), I've got a dozen or so pad mounts rated 13.8kV delta to 480Y/277V. Here's my questions:

Since the service is upstream of the transformers, each transformer needs to have a grounded conductor or neutral AND a ground conductor to the 480V switchboard. True?

Also, the ground conductor is a "secondary bonding jumper" and therefore, needs to be sized in accordance with Table 250-66 and not 250-122.

Just looking for a sanity check here. I know that the last statement would be true for an ordinary dry type, I'm just wondering if the fact that the transformer is more than 600V has any impact on this.

Thanks,

Mike

 

[Smart $]

True. 250.66. None.

 

[augie47]

If you have a non-metallic conduit system from the transformer to the panel, I think an argument could be made to omit the equipment bonding jumper per 250.30 Exception 2.

 

[Smart $]

If you have a non-metallic conduit system from the transformer to the panel, I think an argument could be made to omit the equipment bonding jumper per 250.30 Exception 2.

Ummm... I believe your reference is missing a letter and/or number.

 

[augie47]

Ummm... I believe your reference is missing a letter and/or number.

opps 250.30(A)(1) Exception 2

 

[Smart $]

opps 250.30(A)(1) Exception 2

Being Mike is in MA and thread title is "Supply side bonding jumper", I assume he's under NEC 2011. If so, there's no exception to installing the SSBJ [250.32(A)(2)].

 

[augie47]

Being Mike is in MA and thread title is "Supply side bonding jumper", I assume he's under NEC 2011. If so, there's no exception to installing the SSBJ [250.32(A)(2)].

Makes sense (and I'm glad they dropped that exception)

 

[Smart $]

Makes sense (and I'm glad they dropped that exception)

Actually, the exception is still there... but I don't see how it can be implemented when there is no exception to installing an SSBJ.

 

[don_resqcapt19]

This is just another area where the NFPA is telling us that electricity behaves differently based on who owns the equipment. If this installation was utility owned, there would be neutral bonding at both the transformer and at the building disconnect, but since the installation is customer owned the code tells us that it is not safe to do that. We are required, for customer owned equipment to install the neutral bonding at a single location and install a supply side bonding jumper between the transformer and the building disconnect.

Now with the 2011 code they added 250.30(C) and the application of this new section is not clear to me.

250.30(C) Outdoor Source. If the source of the separately derived system is located outside the building or structure supplied, a grounding electrode connection shall be made at the source location to one or more grounding electrodes in compliance with 250.50. In addition, the installation shall comply with 250.30(A) for grounded systems or with 250.30(B) for ungrounded systems.

i can see this new section as being read to permit neutral bonding at both the transformer and the building disconnect.

 

[augie47]

This is just another area where the NFPA is telling us that electricity behaves differently based on who owns the equipment. If this installation was utility owned, there would be neutral bonding at both the transformer and at the building disconnect, but since the installation is customer owned the code tells us that it is not safe to do that. We are required, for customer owned equipment to install the neutral bonding at a single location and install a supply side bonding jumper between the transformer and the building disconnect.

Now with the 2011 code they added 250.30(C) and the application of this new section is not clear to me.

i can see this new section as being read to permit neutral bonding at both the transformer and the building disconnect.

That is my understanding also, and in discussions, that was the consensus of opinion on the older exception also.
I appreciate your first sentence

 

[Smart $]

...

Now with the 2011 code they added 250.30(C) and the application of this new section is not clear to me.

i can see this new section as being read to permit neutral bonding at both the transformer and the building disconnect.

IMO, it is intended to mimic 250.24(A)(2) earth grounding for service transformers. But I agree, the application of 250.30(C) as written is not clear. Until clarified, I will assume the intent is: 1) grounded conductor to electrode for grounded systems, or 2) SSBJ to electrode for ungrounded systems.

 

[mshields]

awesome feedback

awesome feedback

thank you!