A main breaker of 200 amps will allow a maximum of 200 amps to flow through it without tripping. In a tripped state, no current will flow to the panel. In systems without an external disconnect switch, the main breaker serves as the household disconnect. Turning off the main breaker stops the flow of power to all of the branch circuit breakers in the panel, and therefore to all of the circuits in the house. However, power is always flowing into the panel and to the service lugs even when the main breaker is shut off unless the power is shut off at a separate disconnect switch. Power is always present in the utility service lines and the electric meter unless it is shut off by the utility. The most common cause of a tripped breaker is a circuit overload. If you’re running a high-demand appliance, such as a vacuum, toaster, or heater, and the power goes out, you’ve probably overloaded the circuit. Move the appliance to a different circuit and reset the breaker by switching it to the ON position. If the breaker trips again—without the appliance plugged in—you must call an electrician. There may be a dangerous fault situation in the circuit. A single circuit may contain multiple switches, receptacles, fixtures, and other devices, or it may serve only a single appliance or receptacle. The latter is called a dedicated circuit. These are used for critical-use appliances, such as refrigerators, furnaces, and water heaters. Other appliances, such as dishwashers and microwaves, usually are on dedicated circuits, too, so that they can be shut off at the service panel without interrupting service to other devices. This also reduces the incidence of overloaded circuits. In potentially wet areas of a home, such as bathrooms, kitchens, and laundry rooms, some or all of the outlets must have GFCI (ground-fault circuit-interrupter) protection, provided by GFCI outlets or a GFCI breaker. Bx cable, also known as armored cable, consists of wires running inside a flexible aluminum or steel sheath that is somewhat resistant to damage. It is commonly used where wiring for appliances, such as dishwashers and garbage disposals, is exposed. Conduit is a rigid metal or plastic tubing that protects individual insulated wires. It is used in garages, sheds, and outdoor applications where the wiring must be protected from exposure. Wires running inside NM cable, Bx cable, or conduit are sized according to each circuit’s amperage. Wire size is given in its gauge number. The lower the gauge, the larger the wire, and the more current it can handle. For example, wiring for 20-amp circuits is 12-gauge, which is heavier than the 14-gauge wiring used for 15-amp circuits.
