Bus Bars

[Houston]

I have a question? I was told by someone that the bus bar where the breakers clamp onto (the slots) in residential panels are rated only 100 amps. Sorry for the rough description i dont know how to describe this everyday part of the bus.
For instance you cant have a 100 Amp breaker across horizantally from any other breaker because that slot is only rated for 100 amps. Even in a 200 amp panel. I always thought that the bus in a 200amp panel was rated for 200 amps. And as long as you didnt over rate the box it wouldn,t matter.
I also believe the code says somthing about not having the main disconnect across from anything else, having trouble finding that code thou. But the question is for other then main breaker.
I also did some internet research and couldnt find anything. The reason I ask is because I ran into a 125 standard main on the bus. The siemens box had no labeling inside to check. I would like to know if this puts my customer in danger of melting her bus bar.
Thanks

 

[480sparky]

First I've ever heard of such a thing.

Every breaker can only 'grab' so much of the bus bar, so I don't think the breaker on the other side of the panel has anything to do with the amp rating of the bar.

"Someone" may be confused by 'frame size', meaning you can't get a high-amperage breaker in the same physical dimensions as all the other breakers. 125a is the largest resi-type stab-on breaker I've seen.

 

[augie47]

Although the buss on the panel is rated to carry the full rating of the pane, at times the "stabs" that run off the basic buss have limits. I have seen notice of such limits in the past.
Your panel distributor should be able to get the information foe you from the manufacturer but it probably would not be a bad practice not to put larger breaker directly across from a 100 amp or plus unit.

 

[jim dungar]

A little true stretched in a myth

Yes, the breaker "fingers" have a current rating, this is one reason some 200A breakers take 2x as much space. Over the years, I have seen some breakers built with 'interference' features that would prevent you from mounting two breakers across from each other (Square D NEHB series comes to mind).

But if the panel label does not list any restrictions, and the manufacturer doesn't make special breakers, you are allowed to put in whatever fits.

 

[iwire]

Although the buss on the panel is rated to carry the full rating of the pane, at times the "stabs" that run off the basic buss have limits.

I agree and it is often stated on the panel label.

 

[infinity]

I've seen this in commercial panels as well with a limit of 150 amps per stab. Had a small 400 amp distribution panel with 4-125 amps CB's and they were set up as circuits 1-3-5, 8-10-12, 13-15-17, 20-22-24. The slots opposite of each of the CB's were filled with blanks by the manufacturer.

 

[LarryFine]

Had a small 400 amp distribution panel with 4-125 amps CB's . . .

But, 4 x 125 adds up to more than 400! (j/k )

. . . and they were set up as circuits 1-3-5, 8-10-12, 13-15-17, 20-22-24.

I may not have zig-zagged the breakers like that, but I definitely would have stacked them on one side rather than placing any of them head-to-head, i.e., sharing stabs. I guess their way minimized heating issues.

When I load residential panels, I try to place the 2-pole breakers on one side and the single-poles on the other. That avoids placing two larger breakers on the same stabs, but if I have to, I separate the biggest ones.