How to Wire a Generator Interlock Kit

How to Wire a Generator Interlock Kit

A generator interlock kit is a mechanical device that attaches to your main breaker panel and physically prevents the main breaker and the generator inlet breaker from being on at the same time. This prevents back-feeding power onto the utility lines, which is dangerous to utility workers and illegal in Ontario. An interlock kit is one of the most cost-effective ways to connect a portable generator safely to your home’s circuits.

Ontario Code Requirements

Under the Ontario Electrical Safety Code, any generator connection to a home’s electrical system that can back-feed the utility must have an approved transfer means. A listed generator interlock kit qualifies when installed on an approved panel by a licensed electrician with an ESA permit. DIY installation without a permit is not permitted and creates a safety and liability risk.

Components Required

• Generator interlock kit specific to your panel brand and model
• 30-amp double-pole breaker (or the amperage that matches your generator’s output)
• Inlet box (outdoor-rated, with appropriate male connector for your generator cord)
• 10/3 or 10/4 NMD90 or SO cord rated for the load
• Generator-to-inlet power cord (rated for outdoor use)

How the Interlock Works

The interlock kit slides over the main breaker and the generator breaker. A metal slide plate is designed so that when the main breaker is ON, it physically blocks the generator breaker from being turned ON. When you switch to generator power, you first turn off the main breaker, which releases the slide and allows the generator breaker to be turned on. This makes it mechanically impossible to have both breakers on simultaneously.

Installation Overview

1. A licensed electrician installs a new double-pole breaker in the panel at the position specified by the interlock kit instructions — typically adjacent to or near the main breaker
2. The interlock slide plate is mounted to the panel door or cover using the hardware provided
3. A conduit or cable run connects the panel breaker to the outdoor inlet box
4. The inlet box is mounted on the exterior of the home in a weatherproof location
5. When the generator is needed, the homeowner turns off non-essential breakers, turns off the main breaker, turns on the generator breaker, starts the generator outside, then connects the generator cord to the inlet

What Homeowners Cannot Do Themselves

In Ontario, work inside the panel — including adding a breaker, installing the interlock hardware, or running the circuit to the inlet box — is regulated electrical work that requires an ESA permit and a licensed electrician. Homeowners can connect and disconnect the generator cord at the inlet box, but the permanent installation must be done by a licensed contractor.

EZSMART installs generator interlock kits and outdoor inlet boxes across Ontario. Contact us to get your home generator-ready for the next power outage.

Amir Azimipour

Electrician Since 2008 Journeyman Electrician Designated Master Electrician at EZSMART Corp