guideline for selection of single pole & double pole breaker

Think about what it is you are doing for a second. The job of a circuit breaker is to disconnect all sources of electrical energy from a circuit when conditions warrant such being done. Such conditions include, a short circuit condition or prolonged elevated current level.

Given the standard 120/240 volt single phase consumer service in use in North America... we have two hot wires and a white wire called the "neutral" or "identified conductor" or "grounded conductor". What the white wire is called depends upon where you live in North America.

From either hot wire to the white you have 120 volts. From one hot wire to the other hot wire you have 240 volts.

So... on a 120 volt circuit, to kill the power you need a single pole breaker to break the power flow in the one hot wire and on a 240 volt circuit, you need a two pole breaker to kill the power flow in both hot wires.

This description can be moved out to any power system world wide. The key concept here is killing power flow in live wires. If you had a 6 phase system, you would need a 6 pole breaker.

In North America we also use what are called "split receptacles" where a duplex receptacle will be fed by both hot wires and the white. One hot wire will feed the top set of prongs on the receptacle while the second hot will feed the bottom set of prongs. This is normally used on a counter receptacle. This receptacle will be fed from a two pole breaker. Why? So that all the power is killed to the split circuit when it is turned off for safety.

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