Circuit Breaker Question

[TheJackRabbit]

I hope someone can take the time to answer this question.

For a 240 Volt 50 Amp 8/3/G circuit requiring a 50 Amp or 60 Amp breaker is it possible to connect each 120 volt hot leg to a single pole 25 or 30 Amp breaker and then tie the switch levers?

I ask because a 50 Amp Two pole breaker seems to be 50 Amps on each leg. Am I getting that right? The breaker reads 50/50 on the two switch bar.

I am not sure if these are equivalent breaker protection.

Thanks in advance. There is no one around here I can ask whose opinions I trust.

 

[LAMBCRUSHER]

you are going to have to use a breaker with 50 amps of overcurrent protection on each pole. that is to say a 240 volt 50 amp circuit is drawing 100 amps at 120 volts. the 25 amp breakers-if you could find that size and were able to tie the handles together, would only give you 25 amps at 240 volts. Does this help?


also, a device with 50-60 amps of circuit capacity should be fed by #6 conductors. the option of 50-60 amps indicates that your device may pull more than 50 amps. # 8 is rated for 50 amps.....HTH

 

[John Smith]

I hope someone can take the time to answer this question.

For a 240 Volt 50 Amp 8/3/G circuit requiring a 50 Amp or 60 Amp breaker is it possible to connect each 120 volt hot leg to a single pole 25 or 30 Amp breaker and then tie the switch levers?

I ask because a 50 Amp Two pole breaker seems to be 50 Amps on each leg. Am I getting that right? The breaker reads 50/50 on the two switch bar.

I am not sure if these are equivalent breaker protection.

Thanks in advance. There is no one around here I can ask whose opinions I trust.

The double pole 50 is 50 on each leg, which equals 50. You definitely do NOT want to use two different breakers on the same leg. Use the proper double pole 50 breaker.

 

[PAToyota]

You COULD use two 120V breakers and tie them together - some older panels are actually set up that way. BUT, you would have to use two 50A breakers as explained above. You're pulling 50A from EACH leg - not a combined 50A from the two legs. But for a modern panel best to just go with the 240V 50A breaker and do it properly.

 

[TheJackRabbit]

Fortunately I found a two pole 50 AMP breaker, so I was able to complete the circuit the right way.

I just was not clear about the two single pole breakers tied together- whether that is 25 X 2 = 50 Amps or just 25 Amps, as indicated: 25 & 25 = 25. Each hot leg needs to be at the required Amps. This has confused me for some time but now I think I have it straight.


Many thanks to all of you. Have a great Thanksgiving.

 

[PAToyota]

I guess the confusion is that 240V will draw half the amps than it will at 120V - all else being equal.

Watts = Amps x Volts

So you can see that for equal Watts, Amps will have to double when the Volts are cut in half.

12,000W = 50A x 240V

12,000W = 100A x 120V

 

[Azca]

The rating of the breaker, 50 amps in this case, is the rating of each phase or leg. These are NOT combined. The #8 is a good example here, if each phase was 25 amps then you could use a #10 on each leg.

The #8 MAY be okay IF the conductor is copper and it is NOT an SE cable that is routed in the buildings insulation, or the equipment it terminate in is rated for 75C conductors, and the insulation is rated for 75c. Typically 8cu is limited to 40 amps if it is romex or now (2011 NEC) SE cable or the equipment, at both ends, is limited to 60 deg c or you must derate due to ambient concerns.

Based on what I see this is being used for a range for a newer home (otherwise it wold not be a 3 wire with ground but could be a sub panel...), you can use a 40 amp breaker to feed the range provided the range rating does not exceed 12kw. There is a allowance, FOR A RANGE branch circuit, to be derated to 8kw so a 40 amp breaker will work unless the equipment manufacturer requires a larger conductor...