2-pole breakers ?

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  #1  
Old 05-30-07, 08:27 AM
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2-pole breakers ?

on a 220/240 circuit with a double pole 50 amp breaker ( 2 50amps bonded together ) is this a 50 amp or a 100 amp circuit ?

Could you also use two separate 50 amp breakers for this same circuit..or is the 2-pole something unique ?

Also..I have a new A/C unit that the installers have put a new disconnect box next to the unit. The tube type fuse in the box reads 60 amps. What should the corresponding breaker size be in the main fuse box for this set up...50 amp or 60 amps ?

Thanks, Tim R
 
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Old 05-30-07, 08:37 AM
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A 2 pole breaker labeled 50 is good for 50 amps. Each leg could pull 50 amps before tripping.

A common trip breaker is needed where both hot legs serve one piece of equipment.

The fuses in the disconnect should be whatever size is called for on the label of the equipment.

The 60 amp rating is the maximum load that can be used with this disconnect.
 
  #3  
Old 05-30-07, 08:45 AM
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I agree with everything pcboss said, but I'll just add a few notes.

A double-pole 50-amp breaker is really just two 50-amp single-pole breakers connected together. Each of the two breakers is independently monitoring for 50 amps. Uness there is a fault, the amps on one leg are the same amps as on the other leg (this is true for your A/C, but things are a bit different for appliances like a clothes dryer). Another way to think of this is that the electrons flowing out one breaker are flowing into the other breaker, and then they alternate.

Two things make a double-pole 50-amp breaker different from two single-pole 50-amp breakers: (1) The handles are tied together so that if one trips, they both do. This is a safety thing. (2) They are physically connected side by side, so that they are always installed in adjacent spaces in the panel. This ensures the correct positioning to really get 240 volts.

If the breaker were only there to protect against a current overload, you'd only need the protection of one of the two breakers (because the current would always be the same on the two breakers). However, the breakers also protects against hot-to-ground faults. Since either of the two hot wires could fault to ground separately, you need protection on both wires. Finally, the two poles of the breaker serve to manually disconnect both hot wires when you need to service the appliance.
 
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Old 05-30-07, 09:11 AM
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Thanks guys...still not clear on the 60 / 50 issue. Assuming the a/c calls for a 60 amp disconnect (installed by a/c company installers) is it ok to have the previous 50 amp 2-pole breaker in the main service box feeding the 60 amp disconnect box to the a/c ?

Or should the main service breaker for this service be a 60 amp 2-pole breaker ?

I don't know what the old (30 years) a/c disconnect fuse was...?..but the main breaker has always been 50 amps
 
  #5  
Old 05-30-07, 05:03 PM
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on the a/c unit itself, there will be a sticker that lists a "max overcurrent protection" and "minimum circuit ampacity" or something very close to those statements.

either the breaker or the fuses must be no larger than the "max overcurrent protection" and neither of them can be less than the "min circuit ampacity"

typically the smallest circuit interupter is closest to the appliance. In a situation like this it doesn;t make a lot of difference. As a matter of fact, you don;t even need a fused disconnect at the appliance unless it is required by the manufacturer.
 
  #6  
Old 05-30-07, 05:40 PM
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If the 50 amp doesn't trip then it is fine. If it starts tripping then up it to a 60.
 
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