Is it normal for lights to dim when I turn on the kettle?

A very slight, momentary dip is common in many UK homes and is usually harmless. If the dimming is noticeable and lasts more than a brief moment, it warrants investigation.

Could this damage my electrical appliances?

Significant voltage drops can affect the performance and lifespan of sensitive electronics. Motors in appliances like fridges and washing machines can overheat if the voltage drops too low during operation.

Do I need a bigger electricity supply?

Possibly. If your property has an older, lower-rated supply and you have added high-draw appliances (like an electric shower or electric vehicle charger), the supply may need upgrading. Your electrician can assess this and apply to the DNO for an upgrade.

Would a consumer unit upgrade fix this?

A consumer unit upgrade alone may not fix it if the cause is loose supply connections or an inadequate incoming supply. However, it can help if the issue is poor connections within the board.

Can I just move the appliance to a different circuit?

This can help if the appliance is on the same circuit as the affected lights. But if the dimming occurs across all lights in the house, the issue is at the supply level and moving appliances will not help.

Caution

Updated 30 August 2026

Lights Dim When An Appliance Turns On

Your lights momentarily dip or dim whenever you switch on a high-power appliance like a kettle, washing machine, or electric shower.

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What's happening?

A brief dimming of lights when a large appliance starts up is caused by the sudden current draw pulling voltage down across the circuit. A slight, momentary dip is normal in many homes. However, if the dimming is severe, prolonged, or getting worse, it can indicate an undersized supply, a loose connection, or circuits that need separating.

What usually causes it?

High-draw appliance (kettle, electric shower, washing machine, tumble dryer) causing a temporary voltage drop on a shared circuit
Undersized supply cable or weak incoming supply for the property
Loose main neutral connection amplifying the voltage drop
Lighting and socket circuits sharing connections that should be separate
Ageing or corroded wiring increasing resistance and making voltage drops worse
Consumer unit connections becoming loose over time

Is it dangerous?

A brief, slight dim when a heavy appliance starts is generally harmless and quite common. However, if the dimming is pronounced (lights visibly dim to half brightness or more), lasts more than a second, or is getting progressively worse, it suggests a wiring issue that could lead to overheating. A deteriorating loose connection can become a fire risk.

Can I fix it myself?

Note which appliance causes the dimming and how severe it is. If the lights only dip slightly for a fraction of a second when the kettle boils, this is likely normal. Try plugging the appliance into a different socket. If the dimming happens regardless of which socket you use, the issue is in the main supply or consumer unit connections. You cannot fix that yourself.

When should you call an electrician?

Call an electrician if the dimming is severe or prolonged, if it is getting worse over time, if it happens with relatively low-power appliances, or if the lights dim throughout the entire house. Also call if you notice warmth or burning smells around the consumer unit when appliances switch on.