Transfer Switch or Interlock Kit for a Portable Generator

An interlock kit is a metal plate fitted to the face of the existing panel. The Electrical Safety Authority's generator-safety podcast warns that interlock devices sold online which only screw onto the panel's removable front cover are not permitted in Canada, because taking the cover off defeats them, so the kit has to be one approved for that panel. It sits over two breakers, the main breaker and a dedicated generator breaker, and its shape makes it mechanically impossible for both to be on at once. Turning the main off frees the plate to slide, which frees the generator breaker to go on. Turning the generator breaker off is the only way to get the main back on. That geometry is the whole safety mechanism, and it is why the kit has to match the specific panel it goes on.

The rest of the installation is the generator breaker itself, the wiring from that breaker to an outdoor inlet, and the inlet the cord plugs into. There is no separate enclosure. Nothing is added between the utility service and the panel, which is why the labour is short and the price is low. It also means the panel is doing the switching, so the panel's own condition and layout decide whether the kit fits at all.

Kolji Bros. Electrical's Ontario 2026 guide is the anchor for this comparison because it prices all three the same way, supplied and installed: $400 to $800 for the interlock kit, $800 to $1,500 for the manual switch, $1,500 to $3,000 for the automatic switch. The ratios hold at both ends. The interlock is about half the manual price whether you compare the low figures or the high ones, and about a quarter of the automatic price on the same test.

Draper Electric's separate line items explain where the interlock's saving comes from. Draper prices transfer switch installation labour at $200 to $500 for a straightforward two to four hour job and the switch unit itself at $200 to $2,000. An interlock kit removes the enclosure, the second set of feeders and most of the labour hours from that list, leaving the plate, a breaker, a short run to the inlet and the inspection. Amps Logics Electric's 2026 GTA rate guide puts standard licensed electrician labour at $95 to $140 per hour, which is the rate those saved hours are billed at.

A caution on comparing bids: the permit is a real cost that some quotes carry and others omit. Draper Electric prices an ESA electrical permit for transfer switch work at $50 to $350, and Kolji Bros. Electrical prices the ESA permit and inspection on a generator's electrical side at $150 to $350. Ontario's 13% HST applies to hardware and labour on all three routes. Two interlock quotes a few hundred dollars apart may be describing the same work with the permit folded into one of them.

The Electrical Safety Authority prohibits connecting a portable generator directly to a wall outlet or panel without an approved transfer mechanism, and it names three that qualify: an interlock, a manual switch and an automatic switch. Choosing the cheapest of the three does not lower the requirement attached to it. A licensed electrical contractor still has to pull the ESA permit, and the work still gets inspected.

The reason is the same in each case. Without a transfer mechanism the generator can push current back onto the utility line, which endangers the crews restoring it, and the same connection carries fire and electrocution risk inside the house. An interlock kit prevents that outcome mechanically, a transfer switch prevents it through its own construction, and a cord run into an outlet prevents nothing.

Neither route makes the generator start itself. That behaviour belongs to an automatic transfer switch paired with a standby generator, and a portable machine in a garage has no way to acquire it from a cheaper switch. Both routes also end at the same ceiling, which is the generator's own output, and neither adds a watt to it. Sizing the machine is a separate decision that the switch choice does not influence in either direction.

The trade doing the work is the same trade in both cases, and the index's own labelling shows how broad that trade is. Each record carries the business type Google Maps assigns it rather than the site's own taxonomy, and across the 480 companies those labels run 306 electricians, 60 electrical installation services, 47 HVAC contractors and 20 electric generator shops, with single-digit and low-double-digit counts for electrical engineers, energy equipment suppliers and corporate offices. Twenty records in the entire index are labelled as generator shops. An interlock kit and a manual transfer switch are both panel-side electrical work, which is what the large majority of these records describe.