What gauge wire and breaker size do I need for permanent outdoor string lights on my pergola?

For permanent outdoor string lights on a pergola, you'll need a dedicated 15A circuit using 14/2 NMD90 wire — but because this is an outdoor installation, the wiring method and weatherproofing requirements are what really drive the project.

String lights are a low-draw load. A typical strand of LED outdoor string lights pulls 15-40 watts, so even running 10-15 strands, you're looking at 150-600 watts total — well within a 15A circuit's 1,800-watt capacity. A standard 15A breaker with 14/2 wire is the right choice for the circuit itself. If you're planning to add other loads to the same circuit (a ceiling fan, outdoor speakers, patio heater), bump up to a 20A breaker with 12/2 wire to give yourself headroom.

Weatherproofing Is the Real Requirement

The wire gauge is the easy part — the installation method is where outdoor circuits get more involved. From your panel to the pergola, you have a few options. Underground runs require either TECK cable or NMD90 pulled through rigid PVC conduit buried at least 600mm deep (the Ontario Electrical Safety Code minimum for residential). Above-ground runs along the house exterior require conduit — liquid-tight flexible conduit or rigid EMT — to protect the cable from UV, moisture, and physical damage. You cannot simply staple NMD90 along an exterior wall and call it done.

At the pergola itself, you need a weatherproof outdoor box with an in-use cover (the bubble-style covers that stay closed even with a plug inserted). The outlet must be GFCI-protected — this is a hard requirement under the Ontario Electrical Safety Code for all outdoor outlets, no exceptions. You can either install a GFCI outlet at the pergola, or protect the entire circuit from a GFCI breaker at the panel. Given that string lights often use standard plugs rather than hardwired connections, a weatherproof GFCI outlet at the pergola is the most practical approach.

GTA-Specific Considerations

Toronto's 50+ freeze-thaw cycles per year are hard on outdoor electrical installations. Underground conduit can shift with frost heave, and any above-ground conduit connections need to be properly sealed to prevent moisture infiltration. If your pergola is a newer structure in a post-2000 suburban home in Markham, Vaughan, or Mississauga, the run from your panel to the backyard is likely straightforward. If you're in an older Toronto neighbourhood like the Beaches or Leslieville with a century home, your electrician will need to assess your panel capacity and existing outdoor wiring situation before adding a new circuit.

An ESA permit is required for this project — you're adding a new circuit, which is firmly in permit territory regardless of how simple the end use seems. Permit cost runs $100-$200 for a single circuit addition. The full project — new 15A outdoor circuit, underground or conduit run to the pergola, weatherproof GFCI outlet with in-use cover, and ESA permit — typically runs $600-$1,200 in the GTA depending on the distance from your panel to the pergola and how the wiring needs to be routed.

Practical Tips

Don't use indoor-rated extension cords to power your string lights permanently — this is one of the most common outdoor electrical shortcuts and a genuine fire and shock hazard, especially in wet conditions. If your string lights plug in rather than hardwire, the outdoor GFCI outlet is the right permanent solution. Make sure the string lights themselves are rated for outdoor use (look for CSA-approved wet or damp location rating on the packaging).

This is a job for a licensed electrician. The outlet swap at the end is simple, but running a new circuit with proper outdoor wiring methods, weatherproof boxes, and GFCI protection requires an ESA permit and professional installation. Need help finding a licensed electrician for your pergola project? Toronto Electrical Repair can match you with local GTA electricians for free — browse the directory at torontoconstructionnetwork.com/directory?trade=electrical.