What is this?
Lights that are suddenly brighter than normal indicate that too much voltage is reaching the fittings. In the UK, mains voltage should be 230V ±10%. If voltage rises significantly above this, bulbs glow excessively bright and appliances can be damaged. This is a serious electrical fault that needs immediate attention.
Common causes
- Lost or broken neutral connection causing voltage imbalance between phases
- DNO supply fault causing overvoltage to the property
- Loose neutral at the meter or consumer unit creating floating voltage
- Faulty voltage regulator on the incoming supply
- Neighbouring property's load changes causing voltage swings on a shared supply
- Lightning or power surge that has damaged the supply regulation
Is it dangerous?
Yes, this is dangerous and should be treated urgently. Overvoltage will blow bulbs, burn out LED drivers, damage electronics and appliances, and can cause overheating in wiring and fittings. A lost neutral is one of the most dangerous domestic electrical faults — it can send up to 400V through circuits designed for 230V. If your lights suddenly become brighter, turn off the main switch immediately and call an electrician.
Can I fix it myself?
Turn off the main switch at the consumer unit immediately to protect your appliances and wiring. Unplug sensitive electronics. Check with neighbours — if they have the same problem, it is a DNO supply fault and you should call 105. Do not turn the power back on until the cause has been identified and fixed.
When to call an electrician
Call an electrician immediately. Overvoltage is an emergency. If you also smell burning, hear buzzing, or see sparks, stay well clear and call the emergency number. If the DNO confirms their supply is normal, the fault is in your installation and needs urgent professional repair.
What will an electrician do?
Measure the incoming supply voltage immediately
Check the neutral connection at the meter, cutout, and consumer unit
Test for voltage imbalance across circuits
Contact the DNO urgently if the fault is supply-side
Repair or replace any damaged neutral connections
Test all circuits and appliances for damage after the fault is resolved
Typical cost
£100 – £350
Emergency callout rates apply. DNO supply faults are repaired for free. If the neutral connection inside your property has failed, repair costs depend on the location and extent of damage.
