What is an interlock kit for a generator?

An interlock kit is a mechanical safety device installed on your electrical panel that prevents your main breaker and generator breaker from being on at the same time — making it a code-compliant, cost-effective alternative to a full transfer switch for connecting a portable generator to your home.

Here's the core problem it solves: when your power goes out and you run a generator, you absolutely cannot have your home connected to both the generator and Hydro Ottawa's grid simultaneously. If utility power comes back on while your generator is feeding the panel, it creates a dangerous condition called backfeed — where electricity travels back up the line and can electrocute Hydro Ottawa lineworkers restoring power in your neighborhood. It can also destroy your generator instantly.

How It Works

An interlock kit is a sliding metal plate that physically bolts onto your panel door. It's machined specifically for your panel brand and model (Square D, Siemens, Eaton, etc.). The plate is positioned so that when your main breaker is in the ON position, it physically blocks the generator breaker from being switched on — and vice versa. You can only have one or the other active at any given time. It's a purely mechanical solution, no electronics involved, which is part of why it's reliable and relatively affordable.

To use it, you'd plug your generator into a generator inlet receptacle (a weatherproof outlet installed on the exterior of your home), run a properly rated cord to the generator outside, start the generator, shut off your main breaker, slide the interlock plate, and turn on the generator breaker. You then selectively turn on the circuits you want to power.

Ottawa-Specific Considerations

In Ontario, installing an interlock kit requires an ESA permit because it involves adding a new circuit (the generator inlet) and modifying your panel. The work must be done by a licensed electrical contractor. The interlock kit itself must be a listed device — meaning it's approved and designed specifically for your panel model, not a generic aftermarket plate.

Typical installed cost in Ottawa for an interlock kit with a generator inlet receptacle runs $400 – $800, depending on panel location and how far the inlet needs to be from the panel. This is significantly less than a manual transfer switch ($800–$1,500) or an automatic transfer switch ($2,000–$4,000+), making it a popular choice for homeowners who want a safe, legal hookup for a portable generator without a large upfront investment.

Is It Right for You?

An interlock kit is a great option if you already own or plan to buy a portable generator and want a permanent, safe connection method. The main trade-off versus an automatic transfer switch is convenience — you have to manually start the generator, go to your panel, and switch things over yourself. For whole-home backup with a standby generator, a proper automatic transfer switch is the better solution.

If you're considering a generator setup for your Ottawa home, Electrical Ottawa can assess your panel, recommend the right interlock kit for your specific panel brand, and handle the ESA permit and inspection. Request a free estimate to get started.