Horizontal Ground Bus Bar (MCC) - Amps Rating?

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angrymonkey

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This is something I was surprised I didnt know. I have been searching around trying to find ratings on this horizontal ground bus bar standard in most MCC's.

I can find plenty of information on how it is a standard, with a vertical bar optional, but no rating.

Any ideas out there?

Whats the amperage rating on a 1/4" x 2" tin-plated copper bus bar?


Thanks for any time.
 
I think the rating could vary depending on how it is mounted. Such as being mounted in the back of a can. Or useing a jumper.
Put a megger on it.:smile:
 
angrymonkey said:
This is something I was surprised I didnt know. I have been searching around trying to find ratings on this horizontal ground bus bar standard in most MCC's.

I can find plenty of information on how it is a standard, with a vertical bar optional, but no rating.

Any ideas out there?

Whats the amperage rating on a 1/4" x 2" tin-plated copper bus bar?


Thanks for any time.
Click to expand...

Do you expect current to flow continuously? If not then you only have to worry about short time rating.

Generally, 1000A/sqin. current density was a rule of tumb, but with the increase of allowable temperature rise to 65C from 55C, I think that rule is gone.
 
angrymonkey said:
(cut)I have been searching around trying to find ratings on this horizontal ground bus bar standard in most MCC's.

(cut)
Whats the amperage rating on a 1/4" x 2" tin-plated copper bus bar?
Click to expand...

All of the MCCs I have seen, the ground bus is rated for the SSC rating of the MCC. If the MCC is braced for 42kA, so is the ground bus.

The IEEE also has some guidance, based on short term temp rise, probably the Redbook. I can't look right now, but I'll check later - unless I get lucky and someone beats me to it.

cf
 
I have an old "Anderson Electrical Connectors" book which give a current rating of 647 amps for a 1/4" X 2" copper bar. The 2" side is to be vertical. That is a continuous rating.
 
am -
I got a chance to check IEEE 141. They are no help on SCC ratings for bare copper. I'd stay with the MCC SCC rating.

Of course, I am assuming you are after a SCC rating, since one would never expect a ground buss to carry a continuous current.

cf
 
Cold Fusion said:
All of the MCCs I have seen, the ground bus is rated for the SSC rating of the MCC. If the MCC is braced for 42kA, so is the ground bus.

The IEEE also has some guidance, based on short term temp rise, probably the Redbook. I can't look right now, but I'll check later - unless I get lucky and someone beats me to it.

cf
Click to expand...

SCC rating has more to do with the mechanical bracing of the bus and it's mechanical configuration rather than thermal rating. A short circuit will surely melt the bus UNLESS it is interrupted.

When a bus' ampere rating is asked it usually refers to the continuous current rating for a maximum speciifed ambient temperature and allowed temperature rise.

In the case of bus ratings, phase busses primary function is continous current rating and sort circuit rating does not come into much consideration.

In the case of ground bus the rigidity of the bus itself and its bracing are the primary considerations, continuous current carrying capacity is hardly a concern.

A sport analogue from the recently completed Olympics; the difference between a sprinter and a Marathon runner.:grin:
 
Thanks for the info.

I spoke with a few vendors who kicked me over to their factory guys. Most seem to agree with a rating around 600A typical that they list for there horizontal bus.


Cheers.
 
Typical vertical ground bus unless specified otherwise is a 1/4 x 1" steel bar from most of the big mfg. As an option a vertical copper ground bus is available.

The typical phase vertical bus rating is 300A unless the calculated connected load for the vertical section is exceeds 300A, in this instance an optional 600A vertical bus assembly is available. Copper is the common material for the vertical phase bus.

300A = 1/4 x 1" (copper)
600A = 1/4 x 2" (copper)
 
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