EZSMART Corporation, ESA/ECRA #7012690 , North York , Ontario
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Basements finished into rental units. Detached garages converted to workshops. In-law suites over the garage. Every one of these Ontario renovations shares a common electrical question — do you need a subpanel? A subpanel is one of the most useful pieces of hardware in a modern GTA home, but it is also one of the most misunderstood. This guide explains what a subpanel is, when Ontario homeowners need one, how it is sized, and where the Ontario Electrical Safety Code draws the line between a subpanel and a full service upgrade.
Direct answer: a subpanel is a secondary electrical panel fed from your main panel by a single heavy “feeder” cable. It has its own busbars, its own row of breakers, and its own main disconnect, but its total capacity is limited by the feeder breaker back at the main panel. Think of it as a satellite office — same company, remote location, sized for the local workload.
A typical Ontario residential subpanel is 60 or 100 amps, fed from a 60-amp or 100-amp double-pole breaker in the main. It usually holds 12, 20, or 30 breaker spaces — more than enough for a finished basement, a detached garage, or an added rental suite.
Direct answer: a subpanel is fed by a four-conductor feeder cable — two hots, one neutral, and one bond — sized to match the subpanel’s rating. A 60-amp subpanel takes 6/3 NMD-90 or the equivalent; a 100-amp subpanel takes 3/3 NMWU or aluminum SER cable. The neutral and bond are strictly separate at the subpanel — they are only bonded together at the main panel or at the service entrance.
Direct answer: choose a subpanel when the main panel has spare feeder capacity but no more physical space for breakers. Choose a service upgrade when the main panel is at or near its total amperage limit — no subpanel fixes that.
A concrete Ontario example: a 100-amp main panel with 12 free amps of capacity and only 4 open breaker spaces cannot accept a 60-amp subpanel — the feeder alone exceeds the available amperage. That home needs a service upgrade. A 200-amp main panel with 80 free amps and 6 open breaker spaces is a perfect subpanel candidate — lots of capacity, not enough physical room. Our post on whether you need a panel upgrade covers the decision in more detail.
Direct answer: the four mistakes ESA inspectors flag most often on residential subpanel installs are (1) bonded neutral and ground at the subpanel, (2) undersized feeder cable, (3) missing four-conductor feeder (running only three conductors and reusing the ground as a neutral), and (4) an unlabeled feeder breaker at the main.
The Electrical Safety Authority considers a bonded-neutral-at-subpanel install a serious safety writeup because it puts return current onto the equipment ground, which can shock anyone touching a metal appliance downstream. This is one of the most common DIY errors we correct on service calls. Do not attempt subpanel installation as a homeowner unless you have a licensed contractor involved.
Direct answer: a typical 60-amp basement subpanel install in the GTA costs $1,500-2,500 including the panel, feeder run of up to 15 metres, ESA permit, and inspection. A 100-amp subpanel or one requiring a longer feeder run climbs to $2,500-4,500. Detached garage subpanels with an underground feeder run to the house cost more due to trenching.
The cost of a subpanel is almost always less than a full service upgrade if the main panel has capacity. If you are debating between the two options, a written load calc from a licensed contractor answers the question definitively.
In our experience installing subpanels across the GTA — basements in Etobicoke, garage conversions in Vaughan, in-law suites in Scarborough — the single detail that saves homeowners the most money is oversizing the subpanel physical enclosure while sizing the feeder correctly for today’s load. A 20-space subpanel costs $40 more than a 12-space and gives you room to add circuits later without touching the panel or the feeder. Homeowners who buy the smallest subpanel that fits today’s needs almost always call us back within a few years to swap it for a bigger one — same feeder, same location, just a bigger box.
Planning a finished basement, garage conversion, or in-law suite in your GTA home and want an ESA-certified electrician to spec and install the subpanel? Call us at 416-838-9006 or visit our contact page — we will get back to you the same day.
Electrician Since 2008 Journeyman Electrician Designated Master Electrician at EZSMART Corp
