What is a Main Breaker?

Electrician doing electrical work in breaker box
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Your electrical panel is full of circuit breakers, running from top to bottom of the service panel. The odd numbered breakers are located on the left and the even numbered circuit breakers are on the right. Atop the many circuit breakers is a larger circuit breaker that is used to turn the entire circuit breaker panel on or off. It is known as the main breaker. It plays probably the most important function in the whole circuit breaker panel.

It is a means of disconnect for the entire panel. But you may ask what makes it different from the rest of the circuit breakers within the panel.

So, what is a main breaker anyway? You'd think that it is something special having a name like that. Actually, the main breaker is the breaker that the feeder wire connects to. This breaker is a two-pole breaker that is connected to 240 volts to power your home. The main breaker acts as the disconnecting means to the entire power load of your breaker box. With it off, there is no power being fed to the buss bar that feeds the branch circuit breakers. The branch circuit breakers are the circuit breakers that feed individual circuits or loads. These may be lighting circuits or used to feed appliances or just general power outlets.

The main breaker is usually located atop the rest of the breakers in a panel, but sometimes the breaker panel is installed upside down.

In this case, the main would be at the bottom. Some main breakers are bolted in place and others are snapped into place just like the branch circuit breakers.

Main breakers come in different sizes, but 100 and 200-amp breakers are generally used in residential installations. In older homes, you may still have a 60-amp service and I personally have seen a 30-amp, 120-volt main service.

If you think you are short on power, think about that installation!

Main breakers are designed to trip if the amperage rating exceeds the value labeled on the breaker. For instance, if you have a 100-amp main breaker in place, if the amperage exceeds 100 amps, the breaker will trip. This is what is supposed to happen, that is if the circuit breaker is functioning correctly.

There are a number of reasons why breakers trip. It may be lightning strikes, power surges from the utility company, or you may have overloaded your electrical panel. I have actually seen a main circuit breaker trip before the 20-amp circuit breaker tripped! The defective circuit breaker was removed and discarded, but it really makes a guy think when you see something like that happen. 

If your electrical panel's main breaker does trip, turn off the branch circuit breakers before resetting the main breaker. There is a simple reason for this and it just makes great sense. You see, there are electrical loads, including motor circuits, that you don't want to come on at the exact same time, which is what would happen if you just flipped the main breaker back on. Starting to load the electrical panel up one breaker at a time is a much wiser choice.

After you have turned off the main circuit breaker and the individual circuit breakers, you can turn the main breaker back on. the main circuit breaker,  Then, one at a time, start turning on breakers again. The idea here is not to dump the entire power load on the main breaker all at once. While turning on any breaker, stand off to the side of the electrical panel before you start turning on the circuit breakers. It is advisable to wear safety glasses and turn your head while turning the circuit breaker on. By doing this, you will protect yourself from any possible electrical flash, sparks, or explosion blowing into your face or body parts. Always practice electrical safety while turning on and off circuit breakers and working in an electrical panel.If the breaker trips again, you may be well advised to call in a professional.