Circuit breaker

The circuit breaker works with a bimetallic strip inside of it that heats up when current passes through it. When the current exceeds the current rating of the breaker, it will cause the breaker to trip. Most tripped breakers will put the switch between on and off so that you can tell it was tripped. To turn it back on you need to set it to off and then back to on.

While circuit breakers are good, there's some things you should know. Since every time the breaker trips there's some arcing, eventually the breaker will wear out and stop working. Also, since it's depending on the bimetallic strip to heat up, many times the rated current of the circuit could pass through it for a brief period of time, which may cause problems with equipment powered on that circuit. This is why you still need surge protection or power conditioning.

When you go take a look at your circuit panel, you hope to see the names or symbols of the brands Murray, GE, or Square D. These are reputable companies that are still in business (at least in the USA). If you see FPE or Federal Pacific, you are living with circuit breakers that may not function properly.

Federal Pacific Electrical went out of business in the early 80's because of a class-action lawsuit that resulted from a bunch of fires in commercial properties due to faulty circuit breakers. Even if the circuit breakers in your home aren't faulty, you can't get replacement parts. And at least one of them is probably faulty, because testing revealed as many as 1 out of every 10 breaker doesn't work properly.

You can get these dangerous circuit breakers changed for roughly $600 (labor and materials). It's a pretty straightforward replacment for electricians, as long as there's nothing else wrong.

Additionally, recent building codes specify AFCI breakers to the bedroom. Like GFCI receptacles/breakers for the bathrooms that protect against shock, AFCI breakers protect against arcing, which can cause fires.

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Fellow noder Transitional Man (who actually has electrician experience) recommends Square D, Siemens (except for Pushamatic), and Cutler Hammer circuit breakers.

A standard household 110V or 220V circuit breaker is a relatively simple device, it breaks the circuit by pulling the electric contacts apart. Low household voltage generally won't create a persistent spark across a small air gap. However, power transmission lines operate at hundreds of thousands of volts, and they need circuit protection, too. A small air gap isn't going to stand in the way of a very large potential voltage difference, it will ionize the air between the contacts and create a long-lasting spark to bridge the gap, which will severely damage the contacts.

Several methods are therefore used to safely break high-voltage circuits:

• Oil-filled: Oil has a higher dielectric constant than air, so it is more resistant to spark formation.

• Vacuum bottle: A spark requires some kind of medium to travel across, it cannot jump across a vacuum. However, very high voltages can vaporize some of the metal on the contacts themselves, creating a path to form a spark.

• Compressed air: These work by blowing out the spark with a blast of compressed air, extinguishing it like a birthday candle.

• Gas insulated: Similar to oil-filled, these are filled with a gas which has a high dielectric constant, usually SF₆ (Sulfur Hexaflouride). Care must be taken to prevent the gas from escaping, as it is a greenhouse gas and harmful to the environment.

• Air break: This version physically slides an insulating shield between the contacts to break the circuit.

High voltage circuit breakers are designed with a specific time delay based on the predicted magnitude of a short circuit and its distance down the power line. This is to ensure that problems in the line affect as small an area as possible. Only the closest breaker to the problem should trip.