Portable generators that supply a few essential devices with power are a cost effective option to keep the power flowing to refrigerators, well pumps and furnaces. Planning and preparing for a power outage requires more than just buying a generator, however. There are several key items to consider and one of those is how to bring power from the generator into the home.
A transfer switch is the easiest, safest and most convenient way to supply your home with electrical power during a power outage, but it requires installation in advance of the outage. A manual transfer switch is the best solution for connecting a portable generator.
A portable generator moves to the place it is needed, and therefore is usually not permanently connected. Most people keep them in their garages or sheds. A special power cord with a plug on each end carries electrical current from the generator to an inlet box, sometimes called a “J-box.” One plug inserts into the generator receptacle, the other end plugs into the inlet box. The power cord has four wires for ground, neutral and two wires that each carry 120 volts, for a total of 240 volts.
The inlet box is mounted on the outside of the home in a location where exhaust fumes from the generator will not enter the home through air vents or windows. The receptacle inside the inlet box is permanently wired to the manual transfer switch.
Transfer Switch Main Breakers
The manual transfer switch has two main circuit breakers similar to the main breakers in your service panel. One of the main breakers connects to the wires that come from the inlet box and control the power from the generator. The other main breaker connects to wires from your service panel and supply the switch with power from the electric utility. These wires connect to a branch circuit breaker in the service panel.
The two main breakers in the transfer switch are connected by a mechanical device that only allows one main breaker to be in the “ON” position at any time. Some transfer switches allow positioning both main breakers in the “OFF” position.
Essential Branch Circuits
The electrical circuits supplied by the generator connect to circuit breakers inside the transfer switch instead of in the main service panel. The wires are disconnected from the original breakers in the main panel and reconnected to new breakers in the transfer switch. The circuit breakers protect the wires from overloading whether the power is supplied from the generator or from the electric utility.
It is important to ensure that all branch circuit breakers adequately protect the wires that connect to them. If the original circuit breaker in the main service panel was fifteen amperes, the new breaker in the manual transfer switch for that circuit must also be fifteen amperes.
Manual Transfer Switch Operation
During normal operation, electricity flows from the utility into the main service panel and is distributed through circuit breakers. The circuit breaker in the main panel that connects to the transfer switch feeds power to the transfer switch, which then distributes that power to the essential circuits through the circuit breakers located within the transfer switch.
When power from the electric utility is interrupted, the homeowner positions the generator near the inlet box and starts the generator before any load is connected to it, then connects the power cord between the generator and the inlet box. The generator is now ready to supply power and the power switch or breaker on the generator is moved to the “ON” position.
At the transfer switch, the homeowner moves the main breaker for the utility supply to the “OFF” position, then turns the main breaker from the generator to the “ON” position. Power is now supplied to the essential circuits controlled by the manual transfer switch.