Bolts for Ground lugs

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jasonrichards

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I had another inspector from another Jurisdiction, give me a call on what the minimum bolt was for a ground lug. The electrician used a 10/32 to connect a 2 terminal ground lug to the enclosier. I cannot find it in the code book. Any responce would be helpful. Thanks
 
I try to use the largest hardware the lug is intended for.

If the lug came with a 1/4" hole I think you could argue it was intended to be used with 1/4" hardware.
 
I like Bob's logic but what does the bolt size have to do with the ground lug connection? The mating surfaces between the lug and the enclosure are what really matters. Who is to say that a 10/32" bolt in a 1/4" hole isn't adequate?
 
jasonrichards said:
I had another inspector from another Jurisdiction, give me a call on what the minimum bolt was for a ground lug. The electrician used a 10/32 to connect a 2 terminal ground lug to the enclosier. I cannot find it in the code book. Any responce would be helpful. Thanks
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Over the years I wondered why our 225 amp panels came factory equipped with a 1/4" bolt connecting those beeg input lugs to the panel buss.

Same question about those ground lugs.

What say you men?

Best Wishes Everyone
 
jasonrichards said:
I had another inspector from another Jurisdiction, give me a call on what the minimum bolt was for a ground lug. The electrician used a 10/32 to connect a 2 terminal ground lug to the enclosier. I cannot find it in the code book. Any responce would be helpful. Thanks
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I think I would defer to the lug manufacturer's instructions.
 
HighWirey said:
Over the years I wondered why our 225 amp panels came factory equipped with a 1/4" bolt connecting those beeg input lugs to the panel buss.

Same question about those ground lugs.
Click to expand...

The mounting bolt/screw is not intended to carry current. The bolt/screw purpose is to provide the clamping force required to hold the lug body in intimate contact with the conductive surface.
 
infinity said:
The mating surfaces between the lug and the enclosure are what really matters. Who is to say that a 10/32" bolt in a 1/4" hole isn't adequate?
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Who is to say that a 10/32" bolt in a 1/4" hole is adequate?

Without having it tested after the fact IMO an inspector could ask for either full size hardware or a paper from the manufacturer.

Clamping pressure between the lug and other material is directly effected by the hardware size and strength.

If a 10/32 is 'OK' in a 1/4" hole is it also OK in a 1/2" hole?

If I was an inspector I might say 'not approved'.

BTW I practice what I preach

Four grade 3 - 1/2" bolts in each lug hole.

300KVA2LG.jpg
 
Thanks for the input, I will tell him that he should require a full sized bolt for the hole or ask for manufacture specs. Plus now I know
 
jasonrichards said:
Thanks for the input, I will tell him that he should require a full sized bolt for the hole or ask for manufacture specs. Plus now I know
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You may be hard pressed to find it written that a full sized bolt is required. As it stands now in this thread there is no evidence that the need to use a full size bolt is more than an opinion. Sorry Bob.:grin:
 
infinity said:
You may be hard pressed to find it written that a full sized bolt is required. As it stands now in this thread there is no evidence that the need to use a full size bolt is more than an opinion. Sorry Bob.:grin:
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I know that you can purchase lugs with holes ranging from 0" (drill your own) up to at least 1/2" all for the same wire size.

If any one lug can have so many different size holes, which size is correct?
 
jim dungar said:
If any one lug can have so many different size holes, which size is correct?
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That is the question. :smile:

Assuming the lug shows up with a 1/2" hole as many do, what is the proper way to use a 1/4" hardware?

Don't forget 110.2 :grin:
 
iwire said:
That is the question. :smile:

Assuming the lug shows up with a 1/2" hole as many do, what is the proper way to use a 1/4" hardware?

Don't forget 110.2 :grin:
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I don't know if anyone can answer that question. We do see listed switchboards with lugs connected to the bus stabs by 3/8" hardware all of the time even though the hole in the lug is 1/2".
 
infinity said:
We do see listed switchboards with lugs connected to the bus stabs by 3/8" hardware all of the time even though the hole in the lug is 1/2".
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I don't recall ever seeing that from the factory. :-?
 
iwire said:
That is the question. :smile:

Assuming the lug shows up with a 1/2" hole as many do, what is the proper way to use a 1/4" hardware?

Don't forget 110.2 :grin:
Click to expand...

What if the lug shows up as 3/8", would 110.2 allow you to enlarge it to 1/2"?
 
According to an application bulletin from FCI/Burndy they suggest but do not require sizing bolts at about 75A per 1/8", so:


>>>
Bolt Diameter = Amps per Bolt*
1/2" = 300A
5/8" = 375A
3/4" = 450A

*NOTE: These current values represent the
current flow enabled by the bolt due to its applied
contact pressure, and NOT the current capacity of
the bolt itself.
<<<<<
 
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