Proper Hardware

[brian john]

I read somewhere that when making bolted connections the hardware needs to be the same size to match the bolt hole, and I have always followed this, I was told this had to do with the UL Listing for electrical distribution equipmnet?

 

[zbang]

Sounds a bit weird to ask, but what sort of bolt holes are you thinking about? The ones I immediately think of lug-to-bus, then I'd want to use the the largest that will fit. OTOH the bus hole might be a different size from the lug.

 

[infinity]

I don't think that there is any written rule. If the bus and the lug have a 1/2" holes and you use a 1/4" nut and bolt to hold them together is that a violation? I've seen double 1/2" holes on #6 AWG lugs, I can't see why two 1/2" nuts and bolts would be required unless it were in the specification.

 

[brian john]

Sounds a bit weird to ask, but what sort of bolt holes are you thinking about? The ones I immediately think of lug-to-bus, then I'd want to use the the largest that will fit. OTOH the bus hole might be a different size from the lug.

Bus tabs in a transformer have 1/2" holes, and we commonly see 1/4" hardware. I was told the UL Listing for proper contact and torque requires 1/2" hardware.

 

[retirede]

Bus tabs in a transformer have 1/2" holes, and we commonly see 1/4" hardware. I was told the UL Listing for proper contact and torque requires 1/2" hardware.

If the hole is actually 1/2”, the appropriate size bolt would be 7/16”.
I don’t think any manufacturer would require a bolt the exact same size a the hole. There are standards for clearance holes for given bolt sizes.

 

[brian john]

If the hole is actually 1/2”, the appropriate size bolt would be 7/16”.
I don’t think any manufacturer would require a bolt the exact same size a the hole. There are standards for clearance holes for given bolt sizes.

I realize this, my question remains is what does UL listing ask for?

 

[Hv&Lv]

1/2” bolt won’t fit in a 1/2“ hole

 

[Dennis Alwon]

Brian, I don;t see anything in the ul book but it may be somewhere else. IDK

 

[infinity]

According to Burndy a 1/2" hole is actually .56".

https://images-na.ssl-images-amazon.com/images/I/81pW9CuDAeL.pdf

 

[retirede]

According to Burndy a 1/2" hole is actually .56".

https://images-na.ssl-images-amazon.com/images/I/81pW9CuDAeL.pdf

In spite of what they call it, that is not a 1/2” hole. It’s a clearance hole for a 1/2” bolt.

 

[Carultch]

1/2” bolt won’t fit in a 1/2“ hole

Usually it will, but it will be a tight fit. It is common to specify clearance holes to exceed the nominal size of the fastener, typically about 1/16" greater than the fastener's nominal size.

 

[electrofelon]

Usually it will, but it will be a tight fit. It is common to specify clearance holes to exceed the nominal size of the fastener, typically about 1/16" greater than the fastener's nominal size.

If we are being really picky, even an "actual" 1/2 hole is probably at least several thousandths over, unless it is reamed, which is unlikely for the applications and equipment we are talking about.. Also, a typical hex cap screw will be 5 thou under even over the grip, more over the threads.

 

[retirede]

If we are being really picky, even an "actual" 1/2 hole is probably at least several thousandths over, unless it is reamed, which is unlikely for the applications and equipment we are talking about.. Also, a typical hex cap screw will be 5 thou under even over the grip, more over the threads.

And then the item with the hole gets a few mils of paint....