What is backfeed and why is it dangerous?
Backfeed is electricity flowing from your generator back out onto the utility lines. It is dangerous because line workers assume lines are dead during an outage, and backfed power can energize them and seriously injure or kill someone. A transfer switch prevents it by isolating your home.
Backfeed can also damage your generator and your own wiring when utility power returns while the generator is still connected. Both sources out of sync can destroy equipment in seconds.
This is the main reason homemade connections, like plugging a generator into a dryer outlet with a male to male cord, are unsafe and should never be used.
What is the difference between automatic and manual transfer switches?
An automatic transfer switch senses an outage, starts the generator and moves your circuits over by itself, then switches back when utility power returns. A manual transfer switch is moved by hand after you start the generator. Both keep the utility and generator connections separate.
Automatic switches are typically paired with standby generators that run on natural gas or propane. They are convenient, especially if you are away or have medical equipment or a home office.
Manual switches suit portable generators. They cost less in equipment but need someone home to start the unit and flip the switch.
Is an interlock kit an acceptable alternative?
Yes, a manual interlock kit installed on the main panel is an approved way to prevent backfeed when it is the right fit for the panel. It is a mechanical plate that stops the main breaker and the generator breaker from being on at the same time.
Not every panel has an approved interlock kit available, and the generator's inlet, cord and breaker must be sized correctly. Those details are why the work is permitted and inspected.
Interlocks power the whole panel, so you manage the load by choosing which breakers to turn on. A transfer switch with selected circuits can be easier to manage.
How are circuits chosen for a transfer switch?
Circuits are chosen by what you need most during an outage, such as the refrigerator, lights, a medical device, internet and one or more cooling circuits. The electrician matches those loads to the generator's capacity so it is not overloaded.
In Arizona, cooling is often the deciding factor. A central air conditioner draws far more power than most circuits, so the generator size and whether to include the AC need careful planning.
A load calculation protects the generator and your equipment. It is part of what a licensed electrician does before choosing a transfer switch model.
Does a transfer switch need a permit?
Yes, installing a transfer switch or interlock is typically permitted and inspected, and it should be done by a licensed electrician. Permits ensure the wiring, grounding and connections meet code and that the utility connection stays separated from the generator.
Unpermitted generator hookups create problems with insurance claims and home sales. They can also create safety risks for utility crews.
Vortech's licensed electricians can evaluate your panel, recommend a switch or interlock and handle the permit process for the installation.
More questions: Home Generators: 12 Most Asked Questions Answered