## Monday, April 12, 2010

### 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?
You have asked a lot of questions. I will try to answer them (without needlessly rambling).

1. For your 30A single pole breaker, it just means that it will allow only 30A to flow in the circuit before tripping. For 120V circuit, yes, that means 3600W max.

2. If you have a double-pole breaker, it still protects the circuit for the exact same 3600W max. The difference, is that when it trips, it COMPLETELY disconnects both connections to the load, rather than just breaking one connection. Some applications demand this type of safety for their protection.

3. When a water heater is 240 V 4500 W maximum, it means that it can be expected to draw up to 18.5 Amps from that 240 V source.

4. It means that it may DRAW up to 18.5 Amps.

5. No. This question is confusing. If you use a 240V heater at 120V, expect that current will go down to about 9A. (because the resistance of the heater does not change).

6. Again, double-pole breakers are used for safety reasons, where you need to disconnect BOTH leads of your load from the source. This can be for AC or DC circuits.
Reply:For residential wiring in North America;

A 30A single pole breaker can provide up to 30A.

A 30A double pole breaker provides up to 30A but at 240V so power is up to 7200W.

A 240V, 4500W max water heater has 2 or more elements and not all are on at the same time. The maximum power would be 4500 when all the elements are on during high water usage. It would draw up to 18.75 Amps.

A double pole breaker is used since both conductors are ungrounded. The neutral conductor in a 120V circuit is grounded so it doesn't need a circuit breaker. In the 240V circuit both legs are at 120V but opposite in polarity so it is 240V across the two.
Reply:In North American residential applications, we use nominal 230 volt, single phase power. Your electric service provider delivers that power in two streams, each with a potential of 115 volts to the neutral. In the power panel, each of the 115 volt breakers connects only to one stream or the other. The panel then delivers that single stream, plus a neutral connection and a ground connection to each outlet.

If, however, you have an appliance such as a kitchen range, clothes dryer, water heater or air conditioner that requires a lot of power, we use a double pole breaker that takes power from both streams and delivers 230 volts to the appliance.

There is a good reason for this. The "work" that electricity does is calibrated in Watts or VoltAmps = Volts x Amps. Amps measures the number of electrons flowing through the conductor while Volts measures the pressure pushing the electrons through. You can see that increasing either one or both increases the number of Watts -- i.e. the amount of work that can be done.

If, however, you double the amps flowing through a wire, you must significantly increase the size of the wire or it will overheat and melt. Fortunately, you can double the voltage (and the wattage) without increasing the wire size.

So, when an appliance needs four times as much power as is available at an ordinary recepticle, you double the voltage to 230 volts and you double the amperage to 30 amps for a potential of 6900 watts.

BTW. Most North American homes today are provided with 200 amp, 240 volt service by their providers -- except in some natural gas rich regions where many appliances are gas-fired and only 100 amp service is required.

Nominal voltage also varies from one region to another. Some standards are: 110 v, 115 v, 117, 120 v

Is that useful -- or a whole lot more than you wanted to know?

Yeah, yeah I know; some blondes just don't know when to shut up.

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