Why do my lights dim when I use the microwave?

Your lights dimming when you use the microwave indicates your electrical system is struggling to handle the power demand. This is typically caused by an overloaded circuit, undersized wiring, or an aging electrical panel that can't properly distribute power throughout your home.

Microwaves are power-hungry appliances, typically drawing 1,000-1,500 watts (8-12 amps) when operating. When your microwave starts up, it creates a sudden demand for electricity. If your electrical system can't supply this power efficiently, the voltage drops slightly throughout nearby circuits, causing lights to dim. This is especially noticeable with incandescent bulbs, which are very sensitive to voltage changes.

The most common causes include:

Shared circuits - Your microwave and lights are likely on the same 15-amp or 20-amp circuit. When the microwave draws its full power, there isn't enough capacity left to maintain proper voltage for the lights. Kitchen appliances should ideally have dedicated circuits, especially microwaves over 1,000 watts.

Undersized electrical panel - Older homes with 60-amp or 100-amp panels often struggle with modern electrical demands. If you have an older panel (especially Federal Pacific or Zinsco brands), it may not be distributing power effectively. These panels are also fire hazards and should be replaced immediately.

Voltage drop from long wire runs - If your electrical panel is far from your kitchen, or if the wiring is undersized (14 AWG instead of 12 AWG for 20-amp circuits), resistance in the wires causes voltage drop under heavy loads.

Loose connections - Loose wire connections at outlets, switches, or in the panel create resistance, which becomes more apparent under heavy electrical loads. This is a serious fire hazard that needs immediate attention.

In Ottawa, this issue is particularly common in older homes built before 1980, when electrical codes didn't require as many dedicated circuits for kitchen appliances. The Ontario Electrical Safety Code now requires dedicated 20-amp circuits for countertop appliances in new construction.

When to call a professional: If lights dim significantly (more than a subtle flicker), if you smell burning, hear crackling sounds, or if outlets feel warm, shut off the circuit immediately and call a licensed electrician. Never ignore electrical issues - they can cause house fires.

A licensed electrician can diagnose whether you need a dedicated circuit for your microwave ($300-600), a panel upgrade ($2,000-3,500 for 100A to 200A), or repairs to loose connections. Most electrical work requires ESA permits in Ontario, so ensure any electrician you hire is properly licensed.

For a professional assessment of your electrical system's capacity, Electrical Ottawa offers free consultations to help Ottawa homeowners identify and resolve power distribution issues safely.

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Electrical Ottawa connects you with vetted, ESA-licensed electricians from the Ottawa Construction Network:Ottawa Electrical Contractors:

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