Electrical disconnects are switches that isolate all wiring in a home or other building from the source of power, typically the utility power service. Also called the service disconnect, this is the first disconnect device after the utility meter. This disconnect may be a special breaker switch housed in an exterior box enclosure, or it may simply be the main circuit breaker on the home's main service panel. It's also possible for a home to have a service disconnect on the outside of the home, while the main service panel—with its own main breaker—is inside the home. Each of these configurations involves specific wiring techniques and requirements that are not interchangeable. This describes the basic wiring setup for a separate disconnect breaker switch.
Disconnects receive 240 volts and lethal current from feeder lines coming from the utility meter. The feeders and the terminals they connect to on the disconnect switch are live at all times unless the utility has shut off the power to your service. The disconnect switch does not shut off the power in the feeders lines or at the switch connections. Disconnect switches must be installed by a licensed electrician.
Where the Feed Comes From
The electrical wiring to the disconnect is fed from the "load" side, or outgoing side, of the electric meter. The side of the meter that receives incoming power from the utility service lines is called the "line" side. There are two hot wires and a neutral wire. The hot wires each carry 120 volts and are different phases. These phases are normally called "A" and "B" phases. The total voltage, when measured between them, is around 240 volts. These wires connect to the disconnect breaker installed within the disconnect box. The breaker is rated for maximum current, measured in amps. For example, a home with 200-amp service will have a disconnect breaker rated for 200 amps. This is standard for new home construction. Older homes may have 150-amp, 100-amp or lower service capacity.
Feeding the Line Side of the Breaker
The two hot wires connect to the top two lugs of the breaker, called the "line" side of the breaker. The neutral wire connects to the silver-colored lug along the side of the breaker. This wire typically is marked with white phasing tape to signify that it is the neutral wire.
Feeding the Load Side of the Breaker
The bottom of the breaker is for the "load" side wiring. The wires that connect here feed the electric service panel in your home. Two "hot" feeder wires connect to the bottom of the breaker. A neutral feed wire connects to the silver-colored lug along the side of the breaker. This wire is marked with white phasing tape to signify that it is the neutral wire. There will also be a ground wire leaving the disconnect. This ground wire will be slightly smaller in gauge than the two hot wires and the neutral wire, and it connects to the case of the disconnect via a lug (usually the neutral lug that the neutral feed wire connects to).
What Do the Electrical Disconnect Wires Feed?
The electrical disconnect may feed the main service panel (breaker panel) in the home. The feeder wires connect to the main breaker in the panel, and the neutral wire connects to the neutral bus. There will also be a ground wire between the disconnect and the service panel; this must be separated from the neutral feed at the service panel to prevent an improper neutral connection. The neutral wires will all be on one bus, and the ground wires will be on a separate ground bus.