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POWER LOSS & SUPPLY FAULT GUIDE

Lights Dim When an Appliance Starts

Brief minor dimming can happen when motors or compressors start, but obvious or worsening dimming may indicate excessive voltage drop, loose connections, overloaded circuits or supply weakness.

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Stop if there is heat, burning, arcing, exposed parts or damaged supply equipment

Do not remove consumer-unit covers, open electricity meters, disturb sealed cut-outs or touch exposed conductors. Leave affected equipment off and contact a registered electrician, supplier or network operator as appropriate.

MOST LIKELY CAUSES

Start with these

High starting current Fridges, pumps and motors draw extra current when starting.
Loose connection A poor line or neutral connection causes voltage drop.
Overloaded circuit or supply Demand may be too high for the circuit or connection.
Network voltage issue The incoming supply may dip under load.
◫ Symptom variations Match the exact pattern before testing. ⌄
  • Lights dip when fridge starts
  • Whole house dims when shower or cooker starts
  • Only one room dims
  • Dimming is getting worse
  • Lights brighten after the appliance stops
✓ Quick checks Safe checks using front-panel controls and visible information only. ⌄
  1. Check whether the whole property or only certain rooms are affected.
  2. Look for a wider local outage.
  3. Inspect the consumer unit for a tripped breaker, RCBO, RCD or main device.
  4. Check the electricity meter display and prepayment status where applicable.
  5. Attempt one controlled reset only if there are no danger signs.
If power returns: reconnect or restore loads gradually and monitor the supply.
If the fault remains: leave affected circuits off and arrange the correct professional response.
1 Fix 1 — Identify the appliance Follow this check without opening live or sealed electrical equipment. ⌄

Process

Note which load causes the dimming.

Success looks like: One motor or high-power appliance is linked to the dip.
Failure means: Several unrelated loads suggest a supply or connection issue.
2 Fix 2 — Avoid overloaded extensions Follow this check without opening live or sealed electrical equipment. ⌄

Process

Connect heavy appliances directly to suitable fixed outlets.

Success looks like: Local voltage drop is reduced.
Failure means: If whole-house dimming remains, testing is required.
3 Fix 3 — Check for danger signs Follow this check without opening live or sealed electrical equipment. ⌄

Process

Look for heat, buzzing, flicker or burning smells.

Success looks like: No immediate danger signs are found.
Failure means: Any heat or crackling requires urgent isolation.
⌁ Common causes explained Why the power or supply may fail. ⌄

Brief minor dimming can happen when motors or compressors start, but obvious or worsening dimming may indicate excessive voltage drop, loose connections, overloaded circuits or supply weakness.

Power loss can originate inside the property, at the meter, or on the electricity network. Identifying which protective device operated and how much of the property is affected is the quickest way to narrow it down.

⌘ Advanced diagnostics Technician-level testing for a competent electrician. ⌄
  • Measure voltage at the origin and affected circuit under load.
  • Check neutral and line connections.
  • Measure appliance starting current.
  • Assess circuit voltage drop and conductor size.
  • Escalate persistent supply dips to the network operator.
▣ Parts that may need replacing Components commonly linked to this fault. ⌄
  • Loose connection or terminal
  • Socket or isolator
  • Appliance motor or compressor
  • Cable section
  • Supply equipment by network operator
! When to call an electrician or supply provider Conditions that should end DIY troubleshooting. ⌄
  • The fault remains after one controlled reset.
  • There is burning, heat, buzzing, crackling or visible damage.
  • The main switch, RCD or breaker will not stay on.
  • The meter or sealed supply equipment appears damaged.
  • Lights become unusually bright or voltage appears unstable.
  • Only your property is affected and no internal protective device has operated.
? Frequently asked questions Common questions about supply faults. ⌄

Who should I call for a complete power outage?

Check whether neighbours are affected. A wider outage belongs to the electricity network operator; a fault limited to your installation may need an electrician.

Can a faulty appliance cut power to several rooms?

Yes. One appliance can trip an RCD that protects several circuits.

Should I repeatedly reset the main switch or RCD?

No. One controlled reset is enough to establish whether the fault remains.