Thursday, November 19, 2009

Single and double pole circuits and appliances?

What is the difference between a single pole and double pole circuit breaker?





Say I have a 30 A single pole breaker. So that means that it is providing 30 A of current at 120 V. Power = 3600 W.





If I have a 30 A double pole breaker, what does that mean? Each pole is 30 A, I know, and each pole is at 120 V. So is the power still 3600 W from any one pole?





When a water heater is 240 V, 4500 W maximum, what does this mean?





Does it mean it can only receive 18.5 A of current at 240 V?





So, if a double pole breaker is used, does that mean that it can rate up to 35 A, since it is a 120 V?





Why does a double pole breaker have to be used? What is the difference between single and double pole? Does it have to do with AC?

Single and double pole circuits and appliances?
A double pole breaker is just that. It has 2 poles, one on each leg of the panel. The circuit it feeds will have 240V at whatever amperage the breaker allows. A 30A double pole breaker will have 30amps at 240V, or 7200 watts. A water heater rated at 240V and 4500 W, will draw a MAXIMUM of 18.75 amps. You could run that on a 20 A double pole breaker. (4500W/240V=18.75A)





A double pole is used whenever a device requires 240V. Most large appliances run more efficiently at 240V, such as electric ranges, electric dryers, AC compressors, etc. For AC, there is a single pole breaker that runs the furnace (unless you have electric heat). This supplies the power for the electronics of the furnace, as well as for the fan which moves the air. It also supplies a central humidifier, if one is attached to the furnace. The 240V circuit for the AC, which is often a 2 wire feed (no neutral) supplies the power for the AC compressor outside, not the blower as a previous poster mentioned. I hope this helps clear things up for you.
Reply:Breakers are sized to protect the circuit or wiring. If you want go by the code a wire is sized to 80% of its rating. ie; a 4500 watt water @ 240 V would need a #10 copper wire which is rated at 30 amps: 4500w / 240 = 18.75 X 120% = 22.5 amps. A 20 amp rated wire is no good.





Appliance manufacturers use 240v because they can size down the wiring,controlls and construction of the product and it becomes cheaper to build.





ie, if your water heater was 4500watts @ 120volts = 37.5 amps


They would need larger contuctors,controlls etc.
Reply:Double poles allow the circuits to be tripped simultaneously. Double poles are traditionally used for 240v only.
Reply:Lots of questions...lets see





Double pole breakers are used for 240 volts....it supplies 120 volts on each breaker...but it supplies 15A to 60A on each side....it all depends on what is hooked to it.





Double breakers are more of a safety issue. The poles are connected with a cross bar. That way if one circuit is overloaded...as in a dryer...it will shut off the whole thing instead of letting your dryer run with no heat...or worse....letting the heat stay on with no air flow or turning drum which would soon catch fire.





Your water heater shows no more than 4500 watts....which is safe for whatever breaker is on that line....higher wattage heat elements will only cause breaker to trip off all the time.





A/C units are almost always on double poles...one side runs blower and circuit board...while the other side runs the compressor outside.


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