EZSMART Corporation, ESA/ECRA #7012690 , North York , Ontario
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Sizing the breaker for a central air conditioner is one of the most-asked pre-install questions from Ontario homeowners — usually because the AC nameplate lists a big number and the panel has a specific breaker slot available. Getting the size right is not just a matter of “bigger is better.” A breaker that is too small nuisance-trips on compressor start; one that is too large no longer protects the wiring. This guide walks GTA homeowners through what size breaker you need for an air conditioner, how to read the AC nameplate, and what the Ontario Electrical Safety Code says about the sizing math.
Direct answer: the correct breaker size for a central AC is printed on the unit’s nameplate as “Maximum Overcurrent Protection” or “Max Fuse Size” — usually abbreviated MOP or MFS. This is the largest breaker permitted, and it is what the OESC requires you to use as the ceiling. Any smaller breaker is a nuisance-trip risk when the compressor starts.
The MOP number is calculated by the AC manufacturer based on the compressor’s locked-rotor current and the fan motor’s contribution. It is not something to guess or override. Look for it on the metal data plate on the outdoor condensing unit, usually on the side or the top.
These are typical ranges. Always confirm against the specific unit’s nameplate before purchasing the breaker.
Direct answer: the conductor feeding the AC has to be rated for at least the breaker’s amperage. 15-20 amp uses 14 AWG copper. 25-30 amp uses 10 AWG. 35-40 amp uses 8 AWG. 45-60 amp uses 6 AWG. The manufacturer nameplate also lists “Minimum Circuit Ampacity” (MCA) — the smallest conductor size permitted.
Rule 14-104 of the Ontario Electrical Safety Code requires that the conductor’s ampacity be at least the value of the overcurrent device — with specific allowances for motor-load circuits. A common mistake is sizing conductor to the breaker but forgetting the ambient-temperature and grouping derating factors when the cable runs through an attic. Consult a licensed contractor for anything beyond a straight basement run. Our post on why breaker size is about the wire covers the conductor sizing principle in more detail.
Direct answer: every central AC in Ontario requires its own dedicated circuit. You cannot tap the AC off a shared circuit — the OESC and the AC manufacturer both require dedicated overcurrent protection sized to the compressor’s characteristics.
Our post on dedicated circuits covers the requirement in depth. Sharing an AC circuit with anything else nuisance-trips the breaker every time the compressor kicks in.
Direct answer: Section 28-604 of the Ontario Electrical Safety Code requires a local disconnect within sight of the outdoor condensing unit. This is a small weatherproof box mounted on the exterior wall next to the AC — usually a pull-out fuse block or a small switch. It lets a service tech shut off the unit without going into the basement.
The disconnect is separate from the panel breaker and does not change the panel-side sizing. It does add $80-150 to the install cost including the box, the pull-out block or switch, and the labour.
Direct answer: a new dedicated AC circuit installed in a typical GTA home costs $450-900 depending on cable run length and whether the wall behind the panel is finished. Includes the breaker, conductor, box work at both ends, the local disconnect at the condensing unit, and ESA permit. Longer runs and finished walls add cost; short unfinished-basement runs are the cheapest.
The Electrical Safety Authority requires an ESA notification on every new AC circuit install. Contractors bundle this into the quote automatically.
In our experience installing AC circuits across the GTA, the fastest way to avoid a mid-summer surprise is to photograph the AC data plate before you schedule the install. We can confirm the MOP and MCA numbers, verify the panel breaker slot is compatible, and pre-order the exact conductor and disconnect combination before we arrive on site. Homeowners who skip this step sometimes discover mid-install that the panel does not have a slot for the required double-pole breaker — turning a two-hour install into a full panel-review conversation. Ten seconds of photograph beats a day of scope change every time. Our post on panel upgrade signs covers the case where the panel does not have capacity for the new AC.
Adding a central AC to your GTA home and need the right size breaker and dedicated circuit? Book an ESA-certified electrician to size, wire, and permit the install. 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
