mbrooke
Batteries Included
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- United States
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- Technician
Wild guess as stated above: heat dissipation. Middle pole might get toasty.
It's about the potential energy in the circuit.
So if you look closely, you will see that the 2P 125A breakers are only listed as "slash" type, meaning 120/240V. That means that in the event of a asymmetric fault (line to ground), the fault energy seen by the circuit breaker is potentially never more than what will flow at 120V (line to ground). But in a 3 phase 240V delta system, even at the same amount of fault current the asymmetrical fault energy can be 240V to ground, so twice the potential fault energy . That's why you must use "straight" 240V rated 2 or 3 pole breakers in a 240V 3 phase panel and you can only use 1 pole slash rated breakers in a "High Leg" system on the 2 phases that are referenced to ground.
3 pole breakers would never be able to be used in a single phase panel, so they ALL have to be "straight" rated for 240V. When used in a 3 phase panels then, the worst case potential fault energy of an asymmetirical fault on a 3 pole breaker would be 2 phases to ground, so that would be twice the energy potential of a 2 pole 125A slash rated breaker.
Well, you mention the voltage ratings, but I claim bragging rights about the available energy in #19.I did propose this as a possibility in post #12![]()
You know, I bet that less than 2% of electricians are aware of that limit. Thank you.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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You know, I bet that less than 2% of electricians are aware of that limit. Thank you.
I worked for a man during the early 70's that would cut out that out of twin breakers (Bryant) so he could install them in panels not designed for them. I was too new to know that that's a no no.Hey, if the breaker fits, even if you have to defeat the CTL rejection, it's all good![]()