Why no 125A 3 pole breakers?

[electrofelon]

Two pole MCCB's go up to 125A. How come three pole stops at 100? What is the reason? Note I am referring to standard size breakers, I am aware there are special frame breakers that take up multiple spaces per pole.

 

[infinity]

What type of breaker?

 

[electrofelon]

Miniature circuit breakers: square D homeline and QO, Eaton BR and CH, siemens QP or BL.......bolt on doesnt give you the 125 3 pole either. I assume it is something in the product standard that doesnt allow a three pole >100

 

[LarryFine]

Two pole MCCB's go up to 125A. How come three pole stops at 100? What is the reason? Note I am referring to standard size breakers, I am aware there are special frame breakers that take up multiple spaces per pole.

What do you mean by MCCB?

 

[electrofelon]

What do you mean by MCCB?

molded case circuit breaker, but I should have said miniature circuit breaker.

 

[Hv&Lv]

like this?

 

[electrofelon]

No, that is a special frame unit that takes up 6 spaces.

 

[Hv&Lv]

H, I know what your talking about now..
now that I think about it, I’ve never seen one either.

 

[electrofelon]

Everybody makes a 2 pole 125, nobody makes s three pole 125 that takes up three spaces. Why is the man limiting my breaker freedoms?

 

[jim dungar]

Two pole MCCB's go up to 125A. How come three pole stops at 100? What is the reason? Note I am referring to standard size breakers, I am aware there are special frame breakers that take up multiple spaces per pole.

For the most part, the limitation is probably the plug-on connection fingers. conceivably two breakers could be plugged onto one set of fingers. to prevent overloading, the manufacturers stop the single breaker design at 100A max.

 

[Hv&Lv]

I was thinking the stab ratings also, but what gives when they make 125 amp two pole?
I know you can’t overload the rating of the stabs by putting say a100 on one side and a 100 on the other side of a Resi panel.
electrofelon has got me wondering now...

 

[electrofelon]

I guess the mathematical logical brain I have wants a specific technical reason other than someone somewhere deciding "it seemed like a good idea to limit a three pole to 100A". Grasping here, but the only thing I can come up with is, I believe three pole breakers are almost always fully rated while two poles are typically slash rated and maybe that causes some issues in size and design at 125A?

 

[Hv&Lv]

That’s what I’m wondering regarding the stab limitations on maximum amperage per stab.

 

[jim dungar]

I was thinking the stab ratings also, but what gives when they make 125 amp two pole?
I know you can’t overload the rating of the stabs by putting say a100 on one side and a 100 on the other side of a Resi panel.
electrofelon has got me wondering now...

Most likely the 125A version uses the entire stab, and prevents another breaker from being added across from it.

 

[brantmacga]

No, that is a special frame unit that takes up 6 spaces.

That breaker has #4-300kcmil lugs. You couldn’t fit that size in a standard 3-pole size. The two pole QO breakers accept 2/0 max.

My guess is the lug size is the sole reason. The only other thing I can think of is possibly the arc extinction chambers may be required to be larger for some reason.


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[jaggedben]

That breaker has #4-300kcmil lugs. You couldn’t fit that size in a standard 3-pole size. The two pole QO breakers accept 2/0 max.

My guess is the lug size is the sole reason. The only other thing I can think of is possibly the arc extinction chambers may be required to be larger for some reason.

How does that explain that 2-pole are everywhere and 3-pole are not? Why would 3-pole need larger than 2-pole? It has to be something that relates to the number of phases or poles, not merely the amperage.

 

[jaggedben]

A speculative guess would be that the poles require a certain amount of internal space or separation per pole (given amperage as well) and that the equation is not linear. i.e. 3-poles requires disproportionately more space or separation. Perhaps 2-pole breakers are made with the internal components shifted to the outsides of the breaker to achieve the required separation. And thus the middle-pole on the 3-pole may not be able to achieve the same separation.

I have never read a UL standard, I'm just guessing based on requirements I've seen for using the outside poles (only) of certain 3 pole disconnects to acheive higher voltage or amperage ratings.

 

[brantmacga]

Perhaps 2-pole breakers are made with the internal components shifted to the outsides of the breaker to achieve the required separation. And thus the middle-pole on the 3-pole may not be able to achieve the same separation.

Reading through the square d documentation on 110/3, 125/3, & 150/3, it limits you to 20A cb’s on either side. So maybe this is the answer.


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[LarryFine]

I wonder if it has something to do with total available energy?

 

[electrofelon]

I wonder if it has something to do with total available energy?

Yeah heat, good idea. Although then there should technically be a prohibition against have 2 two pole 125's side by side, but that could just be considered extremely unlikely I suppose.