Bolts for Ground lugs

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Learn something new every day. I've only dealt with 2, 5, and 8 in steel. Most folks think the 3 marks on a bolt head mean grade 3 and 6 marks mean grade 6.
 
iwire said:
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
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Would it be ok to use that last hole even though its hangin over the busbar?:rolleyes:
 
jim dungar said:
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?
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Why, whichever size fits your bolts, of course!
 
jim dungar said:
According to an application bulletin from FCI/Burndy they suggest but do not require sizing bolts at about 75A per 1/8", so:
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So I ask again, do they have a recommended way of using a 1/4" bolt in a 1/2" that does not look like a butcher did it?

I have a real issue seeing a standard stamped steel fender washer used on a lug which is usually what we see in the field.
 
amptech said:
"Four grade 3 - 1/2" bolts in each lug hole. "
Question: Where do you buy a "grade 3 " bolt?
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By asking for Grade 3 I force our purchasing department to buy hardware of a known quality in place of the typical junk hardware we use for run of the mill stuff.

I asked for 3 but I may have gotten 5.
 
iwire said:
That is something I wondered as well, my gut reaction is no, and I did not have to.
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You really honestly do not believe there is enough surface contact on that lug for the [potential] last EGC to be able to clear a short? Would an engineer have to determine this situation?

I would be interested to know a for-sure yes/no about that. One can never know too much. :)

~Matt
 
TOOL_5150 said:
You really honestly do not believe there is enough surface contact on that lug for the [potential] last EGC to be able to clear a short?
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I honestly do not know and not knowing should make us go on the side of caution.

In most instances I am sure it would be fine, on the other hand that lug can handle four 600 copper conductors and the fault current that lug could be expected to handle could easily be many hundreds of thousands of amps.
 
TOOL_5150 said:
You really honestly do not believe there is enough surface contact on that lug for the [potential] last EGC to be able to clear a short? Would an engineer have to determine this situation?

I would be interested to know a for-sure yes/no about that. One can never know too much. :)

~Matt
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Maybe the choices were limited but the steel has slots that removed half of the surface area and the whole cabinet looks like it is held together with 1/4" bolts. Its all very well bonded with the 1/2" hardware for sure and Bob left a spot for the next guy. Its nice to find one of those now and then.
 
iwire said:
jrannis said:
Would it be ok to use that last hole even though its hangin over the busbar?:rolleyes:
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That is something I wondered as well, my gut reaction is no, and I did not have to.
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With all the meat in those lugs, I wouldn't have hesitated in the least.
 
LarryFine said:
With all the meat in those lugs, I wouldn't have hesitated in the least.
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And what would you base that decision on?

Your gut feeling?

If the equipment was to melt down for any reason that decision could come back to haunt you.
 
iwire said:
And what would you base that decision on?

Your gut feeling?
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That, and looking at the other three outside lug holes, including the large conductor closest to the cabinet. Why doesn't it need to be nearer a bolt?


If the equipment was to melt down for any reason that decision could come back to haunt you.
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I ain't 'fraid of no ghost! No, the body of that lug is way too thick for its melting to bother me.
 
Does that lug ground anything more than the enclosure ? It seems all the

grounding is taken care for in the lug itself, except for the enclosure.
 
LarryFine said:
That, and looking at the other three outside lug holes, including the large conductor closest to the cabinet. Why doesn't it need to be nearer a bolt?


I ain't 'fraid of no ghost! No, the body of that lug is way too thick for its melting to bother me.
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Well as long as your comfortable with a WAG on something like that because thats all it is.

No science, no research just a WAG.

Whats the worst that can happen other then it failing under a high ground fault condition. :grin:
 
benaround said:
Does that lug ground anything more than the enclosure ? It seems all the

grounding is taken care for in the lug itself, except for the enclosure.
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That lug is at the bottom of a 500 KVA transformer. There are two incoming and four outgoing EGCs along with one main bonding jumper.

Here is the total view and before anyone asks the lugs on the transformer did not stay as they are in the picture.

300KVA1LG.jpg
 
iwire said:
I honestly do not know and not knowing should make us go on the side of caution.

In most instances I am sure it would be fine, on the other hand that lug can handle four 600 copper conductors and the fault current that lug could be expected to handle could easily be many hundreds of thousands of amps.
Click to expand...
iwire said:
Well as long as your comfortable with a WAG on something like that because thats all it is.

No science, no research just a WAG.

Whats the worst that can happen other then it failing under a high ground fault condition. :grin:
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How do you know that the way you have joined these two lugs is adequate? What kind of guess did you make that this would work? Do you have the incoming and outgoing EGCs in any particular order? Did you use an oxide inhibitor?


Some questions for you to think about:
Where are you saying this current will be going and what path along that lug are you saying is the weakest link? What path would the current take if this lug did not have terminal pads?

Do think the area at the edge of the pad is as significant as the area near the bolts as far as current transfer is concerned (do you think the contact resistance is the same)? Sandwich a piece of tissue paper with carbon paper on it between the lugs and see what pattern you get on the tissue paper.

Do you think you may have compromised the current handling capacity of this lug for the 3 used lugs by not using the complete area under the pad?

What is the probability that you will have a fault that utilizes the full capacity of all of the EGCs at the same time?

Some fun reading (see page 29 and 30):
http://portal.fciconnect.com/res/en/pdffiles/brochures/BURNDY+Connector+Theory+-+2007.pdf
 
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