A home generator needs a transfer switch, or other approved transfer equipment, so that generator power stays separated from the utility lines while it powers your home’s circuits. Without that separation, generator power can flow back onto the utility system, which is called backfeed and can endanger utility workers, neighbors and your equipment.
Transfer equipment is the safe way to connect a generator to household wiring.
What Backfeed Is and Why It Is Dangerous
When a generator is connected to household wiring without proper isolation, the electricity it produces can travel out through the home’s service and onto the utility lines.
Utility transformers can increase that voltage on the other side, creating a serious shock hazard for line workers who believe the lines are dead. Neighbors and emergency crews can also be put at risk.
The Consumer Product Safety Commission warns never to power house wiring by plugging a generator into a wall outlet. That kind of connection, sometimes made with a double-ended cord, is extremely dangerous and can also start fires.
How a Transfer Switch Prevents It
A transfer switch changes the source of power for selected circuits from the utility to the generator. While the generator is supplying power, the switch disconnects those circuits from the utility supply.
Because the two sources cannot be connected at the same time, generator power cannot flow out onto the lines. When utility power returns, the switch moves the circuits back.
Protecting Your Home and Generator
Transfer equipment also protects your home. If utility power returns while a generator is improperly connected, the two sources can meet inside your electrical system. That can damage the generator, your wiring and your appliances, and it may cause a fire.
A transfer switch also makes it easier to choose which circuits get backup power, such as a furnace, refrigerator, sump pump and some lights, without running extension cords through the house.
Types of Approved Transfer Equipment
Options include manual transfer switches, automatic transfer switches typically used with standby generators and listed panel interlocks that prevent the main breaker and generator breaker from being on at the same time. Portable generators are often connected through an outdoor power inlet with a proper cord.
The right option depends on the generator, the panel and how you want backup power to work. Not every option works with every generator or panel.
Installing transfer equipment involves the main panel and generally requires a permit and inspection in Denver. It should only be done by a qualified electrician.
Always run generators outdoors, away from windows, doors and vents, because of the carbon monoxide risk.
If you want to connect a generator safely, our generator transfer switch installation page explains the options. Contact us with your generator’s size and type, and we can help you plan a safe setup.