What is this?
Sparking from a consumer unit (fuse box) is one of the most serious domestic electrical faults. The consumer unit handles the full electrical load of your property, and any arcing inside it involves high currents. Sparking indicates a catastrophic connection failure, a short circuit, or a device failure within the board. Under BS 7671, consumer units must be metal-clad to contain any fire from internal arcing — if yours is plastic, the fire risk is significantly higher.
Common causes
- Loose busbar connections arcing under high current load
- Failing MCB or RCD with degraded internal contacts
- Short circuit on a circuit feeding back into the board
- Corroded or damaged main switch contacts
- Incorrect installation — loose terminals, exposed conductors
- Water ingress into the consumer unit causing flashover between conductors
Is it dangerous?
This is an extreme emergency. Sparking inside or from a consumer unit involves the full mains supply and can generate intense heat, fire, and toxic fumes. If you see sparks, flashes, or hear crackling from your consumer unit, do NOT touch it. If the main switch is accessible and the unit is not visibly on fire, turn off the main switch. If there is any doubt about safety, evacuate and call 999.
Can I fix it myself?
Absolutely not. Do not open the consumer unit cover. Do not touch any part of it if you can see sparking or damage. If the main switch is safely accessible and you can turn it off without touching the sparking area, do so. Otherwise, stand well back, evacuate the immediate area, and call emergency services if there are flames or heavy smoke.
When to call an electrician
Call an emergency electrician immediately. If the unit is actively sparking, smoking, or on fire, call 999 first. The electrician may need to coordinate with the DNO to isolate the supply at the main fuse before work can begin. Do not allow anyone to restore power until the electrician has completed repairs.
What will an electrician do?
Arrange for the DNO to pull the main fuse if the unit cannot be safely isolated
Remove the consumer unit cover and identify the source of arcing
Replace any damaged MCBs, RCDs, busbars, or terminals
Replace the entire consumer unit if it is compromised, damaged, or non-compliant
Ensure the replacement is metal-clad and compliant with BS 7671 18th Edition
Test the full installation before restoring power and issue appropriate certification
Typical cost
£200 – £700
If the unit is repairable, costs are at the lower end. If a full consumer unit replacement is required (common after arcing damage), expect £400–£700 including all certification.
