circuit breaker breaking capacity

[karalahana]

Hi, I wonder if two pole circuit breaker has half times the short circuit breaking capacity of single pole circuit breaker? since as we increase the poles on the circuit it means less voltage on the contacts and from there on can we say circuit breaker s.c capacity is inversely proportional to the voltage across the contacts??

 

[waross]

NO.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[karalahana]

so if we have two contact on a circuit instead of one so doesnt it provide us any advantage??

 

[Elec777]

in opposite ,the more the poles the more you can find brekers
with higher breaking capacities.

 

[karalahana]

I mean for the same voltage there must be a difference between single pole and double pole break.Can we say there is a relation between the voltage across the contacts and the breaking capacity? for 10 kA s.c current and 120 volt circuit voltage a single pole s.c breaking capacity must be 10 kA but if we have double an able to break 5 kA contact pair will work true?? if not why? breaking capacity seems to be proportional to the power broken...

 

[waross]

A 240 volt breaker rated for 10 kA interupting capacity will also interrupt 10 kA at 120 Volts.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[karalahana]

no doubt, but I speak about an other situation, if a double contact in series in a circuit opens at the same time mechanically what can we say about the short circuit breaking current capacity of this circuit breaker,it is certain that it will break much more easily than a single contact circuit breaker isnt it? But I guess we cant say that the contacts are supposed to have(here miminum limit for breaking a certain current) half the capacity of a single contact circuit breaker but it is lower than the single contact capacity since the voltage across the contacts are lower and TRV will affect the circuit breaker less so we can have a lower capacity contancts,here is the question, what can we say for a double contact breakers' short circuit break capacity , does it have to the same one with single contact one?

 

[desertfox]

Hi karalahana

Have a look at this file I have uploaded


desertfox

 

[rbulsara]

karalahana:

Perhaps you are mixing up, multiple contacts in series for the "same" pole with two pole circuit breakers. They are not the same topics. What desertfox uploaded is a two pole breaker. While only pole comes in play for a ground fault, for direct line to line fault, both poles will come in play but both will see the same amount of current.

Multiple breaks in a "pole" are commonly employed of high voltage circuit breakers for arc quenching and even at low voltages for DC circuits as DC does not have zero crossing.

For LV ac circuits, single break units have been sufficient. Multiple breaks are more to handle higher voltages and resultant TRVs, than the current

Rafiq Bulsara

http://www.srengineersct.com

 

[karalahana]

no I am not mixing up, I mean if an isolated neutral system phase neutral break circuit breaker is exposed to double break current its both contacts will see the same current but the voltage across the contacts will be half the voltage across the single pole circuit breaker ,so I wonder if this will make using an double break (phase and neutral break) circuit breaker more advantageous than single break one?

 

[ScottyUK]

If the neutral is not bonded to earth, and therefore might reasonably be at a potential relative to earth, then most codes would require the neutral to be switched with the line conductor.


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If we learn from our mistakes I'm getting a great education!

 

[rbulsara]

karalahan:
Then the first answer was correct. NO.

Rafiq Bulsara

http://www.srengineersct.com