A home's electrical system has feeder wires that supply power to the panel and branch circuits that leave the panel to power devices. As you may know, the service feeders connect to the main breaker, which supplies power to the electrical panel for distribution. It normally is connected to a 100- or 200-amp two-pole circuit breaker, This main breaker is the main disconnect for the power supply of the breaker box enclosure.
There are also many other breakers within this circuit breaker box enclosure. These breakers vary from the common 15- and 20-amp breakers to those breakers of 100 amps or more, depending on the size of the main breaker and the load requirements that are needed on each individual circuit. These breakers also come in single- (for 120-volt circuits) and double-pole (for 240-volt applications)styles. They are the current protection devices for the circuits that feed areas, devices such as appliances.
The majority of the circuits in your home are either 15-, 20-, or 30-amp circuits. They are located within your electrical circuit panel. But what is an electrical panel? An electrical circuit breaker panel is the main distribution point for electrical circuits in your home. It usually provides between 100 and 200 amps of power to your home, depending on your home’s load demand. Power comes in to your home from the utility company, through a service entrance.
Electrical circuit load capacity is the total amount of power that your home actually will use. In order to decide how big of an electrical service is needed in your home, one has to do a little math homework.
Older homes often only had a 60-amp electrical service, connected to a fuse panel. I actually lived in one that only had 120-volts coming into it. That's right, no 240-volt service! Now homes have 100- or 200-amp electrical services. You must know the load of the appliances in your kitchen for cooking in order to properly install the right sized wiring and circuit breakers.
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.
Branch-circuit conductors have a minimum rating when it comes to ampacity and size. There is a minimum rating based on circuits of not more than 600 volts. These specific requirements are listed in the 2009 National Electrical Code (NEC) under article 210.19(C).
Branch circuit conductors supplying household ranges, wall-mounted ovens counter-mounted cooking units, and other household cooking appliances shall have an ampacity not less than the rating of the branch circuit and not less than the maximum load to be served. For ranges of 8 ¾ KW or more rating, the minimum branch-circuit rating shall be 40 amperes.