What’s The Difference Between Interlocks & Manual Transfer Switches

If you own a portable generator, or are thinking about purchasing one, you’ve probably already considered the idea of connecting it to your home’s electrical panel. Doing so will allow you to power devices in your home via your home’s electrical system, and will eliminate the need for clumsy extension cords.

And if you’ve done any research, you’ve probably also discovered that the only safe way to connect your portable generator to your home is to use either an interlock or a manual transfer switch. What is usually less clear is which solution would be right for you. Before we get into the key differences between the two devices, let’s look at their similarities.

Both interlocks and manual transfer switches perform the same basic functions:

  • Allow you to connect your generator to your home’s electrical system while following code
  • Allow you to switch between power feeds with simple, hands-on operation
  • Prevent your electrical panel from being supplied by your power from two feeds at once – namely your generator and your utility line.
  • Prevent power from the generator from traveling backwards up your utility line where it can do great harm

While both interlocks and manual transfer switches are simple and relatively low-cost, they should be installed by a licensed electrician.

Now that we’ve established the similarities, let’s examine their differences:

Interlocks are simpler devices than manual transfer switches, and they require just a little more effort to operate. With interlocks, switching the feed from external to generator power is a three-step process: Turn off the main breaker, slide the interlock up, then turn on the generator breaker.

Once you’ve switched the feed, you’ll also have to manually flip some of the breakers in your panel; this will limit your feed to the circuits that your portable generator can successfully power.

Manual transfer switches are slightly more complex, but make things easier on the operator. With a manual transfer switches, all you’ll need to do if flip the switch to the position that corresponds to the feed you want; i.e. generator power or utility power.

Once you’ve switched the feed, the manual transfer switch should already be configured to feed the circuits that you’ve planned to power with your generator.

There is a downside to the extra ease of using a manual transfer switch: They require a little more time and effort to install. So we get to the essential question: Would you pay a little extra to your electrician to save a little of your time in front of your electrical panel?

If the answer is yes, a manual transfer switch is a better bet for you. If not, you’ll want an interlock. Either way, most would agree that both options will seem like worthwhile investments the next time you lose power.