Why does my bathroom light flicker when the fan is on?

Your bathroom light flickering when the fan runs is typically caused by voltage drop on a shared circuit or loose electrical connections. This is a common issue that can range from a simple wiring problem to a more serious electrical hazard that needs immediate attention.

The most likely cause is that your light and fan share the same circuit, and when the fan motor starts up, it draws a significant amount of current that causes a temporary voltage drop. This voltage dip makes the light dim or flicker momentarily. Bathroom exhaust fans can draw 50-100 watts when starting, which is enough to cause noticeable flickering on an overloaded 15-amp circuit.

Loose connections are another serious possibility. If wire connections at the switch, in the electrical box, or at the fixtures themselves have become loose over time, the resistance creates voltage fluctuations when current demand changes. This is particularly dangerous because loose connections generate heat and can cause electrical fires. You might notice the flickering is worse when the fan first starts up, then stabilizes, or it might be constant while the fan runs.

Circuit overloading could also be the culprit. If your bathroom circuit also serves other rooms or high-draw appliances, adding the fan's electrical load might push the circuit beyond its comfortable capacity. Under the Ontario Electrical Safety Code, bathroom circuits have specific requirements, and older homes might not meet current standards.

In Ontario, bathroom electrical work often requires ESA permits and inspection, especially if you're adding new circuits or upgrading wiring. Modern bathrooms typically need dedicated 20-amp circuits for high-draw items, and all outlets within 1.5 meters of sinks must have GFCI protection.

Safety warning: If the flickering is accompanied by burning smells, warm switch plates, or buzzing sounds, shut off the circuit immediately and call a licensed electrician. These symptoms indicate dangerous loose connections that could cause a fire.

What you shouldn't do: Don't ignore persistent flickering, and never attempt to investigate electrical connections yourself with the power on. Even simple switch replacement can be dangerous if you're not familiar with proper electrical safety procedures.

The solution might be as simple as tightening connections or as complex as running a dedicated circuit for your bathroom fan. A licensed electrician can diagnose the exact cause and ensure any repairs meet ESA requirements. For a proper assessment of your bathroom's electrical system, contact Electrical Ottawa for a free consultation - we'll identify whether this is a simple fix or part of a larger electrical issue that needs attention.