What should I do if I smell ozone or a fishy odour near an outlet or light switch?

A fishy or ozone smell near an outlet or switch is a serious warning sign of an electrical fault — stop using that outlet or switch immediately and treat this as a potential fire hazard requiring same-day professional attention.

These odours are not random. The fishy smell most people describe comes from overheating plastic — specifically, the phenol compounds in nylon and PVC insulation and outlet bodies release a distinctive fishy or burning plastic odour when they get too hot. Ozone has a sharper, almost metallic smell similar to what you notice after a lightning strike, and it's produced by electrical arcing — current jumping across a gap where it shouldn't. Either smell tells you something is wrong inside that device or the wiring behind it.

What's likely happening behind the wall

The most common causes are a loose wire connection at the outlet or switch terminal, a failing device (the outlet or switch itself is deteriorating internally), or a circuit that's been chronically overloaded. In older GTA homes — particularly pre-war houses in neighbourhoods like Leslieville, the Annex, or Riverdale with knob-and-tube wiring, or post-war bungalows in Scarborough and North York with aging 15A circuits — decades of use leave connections loose and insulation brittle. A loose screw terminal causes resistance, resistance causes heat, heat causes that smell. Arcing at a loose connection is one of the leading causes of residential electrical fires in Ontario, and it can smoulder inside a wall cavity for hours before becoming visible.

Aluminum branch circuit wiring — common in GTA homes built between 1965 and 1975 — is particularly prone to this problem. Aluminum expands and contracts more than copper with temperature changes, which gradually loosens connections at outlets and switches over time. If your home is from that era and you're smelling something near a device, aluminum wiring should be on your radar.

What to do right now

Turn off the breaker for that circuit at your panel. Don't just stop using the outlet — cut power to the whole circuit, because the fault is likely at the wiring connections behind the device, not just the device face itself. If you're not certain which breaker controls it, use a non-contact voltage tester to confirm power is off before touching anything. If you see any scorching, discolouration, or melted plastic on the outlet or switch face, or if the smell is strong and coming from multiple locations, turn off your main breaker and call an electrician immediately.

Do not ignore this and plan to deal with it next week. Electrical arcing inside a wall cavity can ignite wood framing, insulation, or decades of accumulated dust without any visible warning. The Ontario Fire Code and every fire safety authority in Canada are clear on this — burning smells from electrical components are an emergency.

What a licensed electrician will do

An electrician will pull the device from the box, inspect the connections and the wiring condition, check for scorching or melted insulation on the conductors, and test the circuit for faults. If it's a simple loose connection on a copper circuit in good condition, the repair is straightforward — proper screw terminal connections, a new outlet or switch, and the circuit is back in service. If the wiring behind it shows heat damage, or if it's aluminum wiring without proper remediation connectors, the scope expands. Expect a diagnostic service call in the $150–$350 range; if remediation or circuit work is needed, your electrician will quote from there.

This work requires an ESA permit if any wiring is modified or extended. A like-for-like outlet or switch replacement on an existing circuit doesn't require a permit, but if the electrician finds damaged wiring that needs repair or replacement, the permit requirement kicks in.

One more thing worth knowing: if the smell is strongest at your electrical panel rather than at a specific outlet or switch, that's a more urgent situation — overheating inside the panel itself. In that case, call an electrician immediately and consider calling Toronto Hydro at 416-542-8000 if you're concerned about the service entrance.

Need help finding a licensed electrician quickly? Toronto Electrical Repair can match you with local professionals through the Toronto Construction Network — browse the directory at torontoconstructionnetwork.com/directory?trade=electrical.