Transformer Lug Bolts

[cmj197]

We are currently installing some 30kVA/480▲/208Y transformers. The holes on the transformer bussing are 1/2" and the OEM mechanical lug kits have 1/4" hardware/holes. Is there a standard that says you have to use 1/2" hardware if the holes are 1/2"? I have searched the code and look for industry standards and have come up with nothing, but the QA/QA/Cx team is insisting we use larger hardware.

 

[infinity]

We encounter this often. We just use washers. I know of no standard that requires the bolt size to match the hole. If needed you can use crimp on terminals with 1/2" holes and 1/2" hardware but that is certainly overkill.

 

[busman]

Agreed. We also just use washers.

 

[don_resqcapt19]

I don't like washers but don't know of a rule that says you can't use them. However I buy lugs that have holes that match the busing, and rarely every buy a mechanical lug.

 

[qcroanoke]

I don't like washers but don't know of a rule that says you can't use them. However I buy lugs that have holes that match the busing, and rarely every buy a mechanical lug.

What ever size hole is in the bus is the size the hole in the lug will be and the hardware will be too. Period.

 

[petersonra]

What ever size hole is in the bus is the size the hole in the lug will be and the hardware will be too. Period.

I can see where you would do this, but it's not a code requirement. In fact I once asked Panduit about this very issue and they told me that it didn't matter if the holes in the lug match the holes in the bus.

By the way if you want to, you could use lugs direct which sells IHI mechanical lugs. They have a UL procedure approved to allow you to drill out the holes in the lugs if you want to. However, it is unclear if these lugs have a short circuit current rating. UL assigns them a default rating for use in UL508A panels, but outside of such use it's unclear what if any short circuit current rating they might have.

 

[infinity]

Seems to me that using a 1/2" bolt to land a #6 conductor or smaller conductor is overkill and unnecessary but to each his own. There is nothing wrong with using washers. In fact when you order the transformer with the terminals installed there is often 1/4" hardware used with 3/8" or 1/2" holes straight from the factory.