Electric Panel Buss Stab Maximum Load Limitations?

[larry4406]

As part of getting smart for getting power to my my barn, I was introduced to the concept of buss stab limitations. Totally off my radar. That discussion is here starting on Post 13: https://www.garagejournal.com/forum/showthread.php?t=426614

In my particular case, my house Cutler Hammer 200A panel has a label which says "Branch fingers rated 140A max". To my knowledge, the "finger" is the copper portion of the buss which stabs into the breaker. Thus a single pole breaker stabs one finger while a double pole breaker stabs two fingers. On a 240V circuit both fingers are part of the circuit.

The concept presented in the thread was that I could use a 125A double pole breaker on one side while I had (2) single pole 15A breakers opposite. 125+ 15 = 140 so ok.

This subject made me inspect my existing house panel which has me concerned. I have one location where a double pole 100A is opposite a double pole 50. The 100A is a basement sub panel for the "new" heat pump that was installed shortly after we moved in 6 years ago while the 50A is my air compressor. This would appear to exceed the "Branch fingers rated 140A max"? I can easily move the air compressor double pole breaker down to align with two single pole 15A breakers.

Thoughts?

To make sure I am clear on the stab rating:
Double Pole Opposite 2 Single Poles - Take the double pole rating and add it to the greater of the single pole opposite and make sure less than the stab maximum rating.

Double Pole Opposite a Double Pole - Add the two breaker ratings and make sure less than the stab maximum rating.

Single Pole Opposite a Single Pole - should never be an issue as 20A + 20A would never be a problem.

Thanks again!

 

[oltruckag]

My understanding is that the stab current rating is per pole or each contact made by a breaker. A 40 circuit panel would have 20 stab points.

In your case of the 125a two pole across from two 15a single pole you are not exceeding the stab rating as each stab is 140a.

If it was two 125a two pole breakers across from each other you would have 250a per stab, exceeding the rating of the panel.

If you have a 125a two pole across from a 30a single and 15a single you have two stab points of 155a and 140a, the 30a single violates the listing, so it needs to move or the tandem needs to move.

In theory you could fill the panel with 70a breakers (single or double) and not violate the stab rating. Probably not a good idea, and likely violates some other listing, but with only the stab limit it's technically possible.


Tyson

 

[mm08822]

As part of getting smart for getting power to my my barn, I was introduced to the concept of buss stab limitations. Totally off my radar. That discussion is here starting on Post 13: https://www.garagejournal.com/forum/showthread.php?t=426614

In my particular case, my house Cutler Hammer 200A panel has a label which says "Branch fingers rated 140A max". To my knowledge, the "finger" is the copper portion of the buss which stabs into the breaker. Thus a single pole breaker stabs one finger while a double pole breaker stabs two fingers. On a 240V circuit both fingers are part of the circuit.

The concept presented in the thread was that I could use a 125A double pole breaker on one side while I had (2) single pole 15A breakers opposite. 125+ 15 = 140 so ok.

This subject made me inspect my existing house panel which has me concerned. I have one location where a double pole 100A is opposite a double pole 50. The 100A is a basement sub panel for the "new" heat pump that was installed shortly after we moved in 6 years ago while the 50A is my air compressor. This would appear to exceed the "Branch fingers rated 140A max"? I can easily move the air compressor double pole breaker down to align with two single pole 15A breakers.

Thoughts?

To make sure I am clear on the stab rating:
Double Pole Opposite 2 Single Poles - Take the double pole rating and add it to the greater of the single pole opposite and make sure less than the stab maximum rating.

Double Pole Opposite a Double Pole - Add the two breaker ratings and make sure less than the stab maximum rating.

Single Pole Opposite a Single Pole - should never be an issue as 20A + 20A would never be a problem.

Thanks again!

Your understanding is correct. Tandems and quads create additional scenarios.


If you can easily move the 2p 50a do so. Dont loose sleep if you cant as the 50a is for inrush rating. Continuous loads opposite each other are the real concern.

 

[mm08822]

My understanding is that the stab current rating is per pole or each contact made by a breaker. A 40 circuit panel would have 20 stab points.

In your case of the 125a two pole across from two 15a single pole you are not exceeding the stab rating as each stab is 140a.

If it was two 125a tandems across from each other you would have 250a per stab, exceeding the rating of the panel.

If you have a 125a tandem across from a 30a single and 15a single you have two stab points of 155a and 140a, the 30a single violates the listing, so it needs to move or the tandem needs to move.

In theory you could fill the panel with 70a breakers (single or double) and not violate the stab rating. Probably not a good idea, and likely violates some other listing, but with only the stab limit it's technically possible.


Tyson

There is no such thing as a 125a tandem. A 2 pole 125 amp cb yes.

A tandem cb has 2 cb's in the space of a single full size cb.

Quads are 2 tandems sandwiched together with various combinations of handle ties availabe.

 

[oltruckag]

There is no such thing as a 125a tandem. A 2 pole 125 amp cb yes.

A tandem cb has 2 cb's in the space of a single full size cb.

Quads are 2 tandems sandwiched together with various combinations of handle ties availabe.

Correct, I was incorrectly interchanging tandem with two pole, I was thinking two pole when I typed it but wrote tandem. Corrected to try and avoid confusion later.

Tyson

 

[sberry]

I will agree that the ratings are there for good reason but with non continuous loads not something to lose immediate sleep over.

 

[Norcal]

Correct, I was incorrectly interchanging tandem with two pole, I was thinking two pole when I typed it but wrote tandem. Corrected to try and avoid confusion later.

Tyson

A twin breaker is a two pole breaker it just is not used for
240V applications unless it is a make that allows it like Challenger, Crouse-Hinds, Zinsco/Sylvania, which are all obsolete.

 

[Stuff]

A twin breaker is a two pole breaker it just is not used for
240V applications unless it is a make that allows it like Challenger, Crouse-Hinds, Zinsco/Sylvania, which are all obsolete.

Or the current GE 2-pole slimline. GE slims should be obsolete as well but I guess they feel someone has to be bottom of the barrel and they are it!

 

[Norcal]

Or the current GE 2-pole slimline. GE slims should be obsolete as well but I guess they feel someone has to be bottom of the barrel and they are it!

Eaton BR is the bottom of the barrel I’ll use anything but them, I call them Zinsco II.