Generator Transfer Switch Guide

What’s The Purpose of a Generator Transfer Switch?

They distribute power to key electrical circuits, including those that support critical appliances that are not plug-n-play, such as most furnace blowers, overhead lighting, hard-wired sump pumps, etc. They also serve the important function of isolating generator current from the grid, which is (1) important to protect utility workers from a dangerous condition called “backfeed,” wherein electric current from your generator goes backwards, out of your house and into the grid via utility lines; and (2) serves to protect your household wiring from becoming fried or catching fire once municipal power comes back on line while your generator is also feeding power through the same circuits.

Finally, transfer switches offer a much greater level of convenience – by connecting the generator to home circuits with a flip of the switch, you can easily and safely run power to many different appliances, rather than being forced to run a tangle of heavy duty power cords into the home directly from the generator through open windows/doors.

Is a Generator Transfer Switch Necessary?

Well, not necessarily, but the number of cords and connections that you would need to run from the generator directly to appliances to make use of the power of any generator greater than 5,000 watts would be impractical and defeat much of the utility of unit with this much power. Moreover, you would still have the problem of powering hardwired appliances that do not have a plug – hardwired appliances must be powered through a transfer switch.

On the other hand, if you have a smaller generator under 5,000 watts, and you intend to use it only for powering a small number of appliances that are  plug-in types (so there is no concern for backfeeding into the utility lines or overloading circuits when the lights come back on), then you could certainly get away with running heavy duty extension cords into the home.

What Kind of Transfer Switch Should I Buy?

They come in two basic flavors – manual or automatic. Manual transfer switches, as the name implies, must be turned on/off by hand, just like a light switch when installed correctly. Automatic switches, on the other hand, trigger themselves to “ON/GENERATOR” upon detecting a sudden decrease in voltage or, conversely, to “OFF/UTILITY” upon sensing the recovery of grid power.

While automatic switches are the standard for standby generators, most people opt for simpler, less expensive manual transfer switches for portable generators. For an example of a great all-around manual transfer kit that we’d recommend, click here.

What Size Manual Transfer Switch is Necessary?

The short answer is that the switch must be rated at a wattage equal to or greater than your generator’s running (a.k.a rated or continuous) wattage. So, if your generator produces 6,000 running watts, your transfer switch should be, at minimum, rated for 6,000 watts. Using a switch that is rated for less wattage than your generator is flirting with disaster – don’t do it! The wires can burn up and catch fire, among other things. In contrast, going with a switch that can handle more current than your generator produces – the much better option – is just fine.

As far as how many circuits your switch should have, this all depends on how big your generator is and how many circuits you want to energize during an outage. However, in most cases, the average homeowner using a portable generator should be fine with 6-10 circuits, with 10 being the better choice for larger generators and those seeking additional flexibility to power more circuits should the need arise. For a very nice 10-circuit manual transfer switch & kit that is sufficient for generators up to 7,500 watts, click here.

How Are They Installed?

Manual transfer switches are typically installed indoors (or outdoors if they are the all-weather type) and are connected to the outside via an exterior inlet box – essentially a portal installed on the outside of your home that is hardwired and designed to connect to the generator. An inlet box avoids the need to run a cord directly from the generator into the house through a window. Most good transfer kits come with an inlet already, but if you need to buy one separately, a great little inlet that should work for most users can be found here.

Most manual transfer switches are pre-wired and can be installed in short order by an electrical professional, which is the safest course for most people and what we’d recommend. Of course, sufficiently experienced DIY-types can do it themselves if they are up to it. Here is a video discussing installation of a Reliance Controls transfer switch.

How Are Transfer Switches Used?

Generally speaking, while the grid is functioning, the transfer switch is set to “UTILITY,” allowing power to  flow normally from the utility through your home’s main panel circuit breakers and through the transfer switch – i.e., no power is going to or coming from your generator at this time. When municipal power goes out, however, the homeowner first powers up the generator, connects it to the inlet, and turns the generator’s power switch/breaker to “ON.” Then the user goes inside and flips the transfer switch from “UTILITY” to “GENERATOR.” Whatever you do, make sure to follow the specific instructions and procedures provided for your particular transfer switch carefully.

Have you made sure to check out our Ultimate Portable Generator Buying Guide?