Bus bar bolting

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kdlman

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Ohio, United States
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Power Generator technician
I have a question on the bolting of bus bar together. I have 4" silver plated copper bus bar overlapping and need to know how many bolts are needed for proper compression and current flow. I have seen many installations that use 4- 1/2" bolts in this situation but need an engineering backup for my reasoning to go this way. Presently there are 2- 3/8" bolts holding these bus together that bolt into an insulator, the bolts for the insulator not the bus bar. 2,527 amps at 480 volts is the rated output of the generator, this not accounting for any surges or short circuit current. The bolts have been torqued and evidence of cold-copper flow is there with a 7/8" diameter ring under the bolt areas.

I'd like to get a written source to show those I'm trying to convince this needs to change.
 
Presumably the engineer that designed the bus bar system knows what he's doing. There are probably drawings somewhere with his name on it. You could call him and ask him. Asking more or less random people on the internet such an open-ended question is not going to get you a very good answer.
 
There must be a standard for the size of the overlap and the bolt size. We install a lot of 4000 amp Eaton switchgear and they use 4-3/8" bolts torqued to 20 ft lbs to hold the bus plates together.
 
At this point I don't have access to the engineer and am wanting to get a background before I take this any further up the chain so I don't look stupid, which is what you look like making this comment. This forum isn't 'anybody on the internet' but one that seems to have a heavy background in issues I work with.

So for more background, so you don't assume, this bus bar system has options for the connections for the load cables. Those who made the connections can easily be anyone off the street who can turn a wrench and appears to be just that. Connections are made on a bus bar (I'm calling a secondary connection) that is connected to the main bar the generator leads are on not on the main bars, with 2- 3/8" bolts with small diameter washers. Contact is minimal, being under these bolts with evidence of cold copper deformation, with only 1 hour on the engine.

My guess is there should be 4 bolts, one at each corner for the connection to be correct.
infinity said:
There must be a standard for the size of the overlap and the bolt size. We install a lot of 4000 amp Eaton switchgear and they use 4-3/8" bolts torqued to 20 ft lbs to hold the bus plates together.
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Indeed there should be and that's what I'm looking for here. 3/8 at 20 and 1/2 at 50, how many for connections, but additionally this is a generator with vibration when running.

A 750 MCM crimped connector has 2 bolts so a 4"bus should have 4, I'm looking for code requirements



edited out the derogatory comments. not needed
 
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kdlman said:
A 750 MCM crimped connector has 2 bolts so a 4"bus should have 4, I'm looking for code requirements
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I don't think that you'll find a code requirement if you're looking in the NEC. This would be a listing or something like a NEMA manufacturing standard.
 
For what it's worth, a diesel electric locomotive has 2 to 4 bolts on the bussbars coming off the "generator ". Can't think of any environment that would have more vibration than a locomotive going down the rails.
 
jim dungar said:
Have you searched the internet? I just found a bus bar design guide at https://electrical-engineering-portal.com. it looks like the guide is from copperalliance.org.uk.

Do your joint use large diameter washers?

Crimp lugs use two hole to prevent twisting not to reduce the contact resistance.
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Jim, this is exactly what I was looking for! Thank you so very much. I did search the internet under ‘bolting of bus bar’ but didn’t find what I needed.
 
petersonra said:
Presumably the engineer that designed the bus bar system knows what he's doing. There are probably drawings somewhere with his name on it. You could call him and ask him. Asking more or less random people on the internet such an open-ended question is not going to get you a very good answer.
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Petersonra, I got what I was looking for in just a couple responses, but thanks for your input.
 
kdlman said:
Jim, this is exactly what I was looking for! Thank you so very much. I did search the internet under ‘bolting of bus bar’ but didn’t find what I needed.
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Yeah, it sometimes feels weird to be looking to conductor manufacturers for application engineering. Living in the 'end user' or 'installer' world, where the NEC is dominant, we don't think of the resources a new product developer would use.
 
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Fwiw, the washers should (need) to be bellevile or constant torque nuts... Dare i say bolts should be grade 8....
 
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