⚡ Power Cut: Fuse Board Tripped—What To Check First

Last updated: February 2025

Everything goes dark. Fridge stops humming. WiFi router beeps off. You check your fuse board (consumer unit)—something's tripped. A switch has flipped to "off".

Here's what to check, how to reset it safely, and when to call an electrician instead of just "turning it back on and hoping".

RCD vs MCB: What's What?

Your fuse board has two types of switches:

1. RCD (Residual Current Device) - usually the BIG switch:

• Protects YOU from electric shock
• Detects current leaking to earth (faulty appliance, damaged cable)
• Cuts power to multiple circuits when it trips
• Usually labeled "RCD" or "Test" button present

2. MCB (Miniature Circuit Breaker) - the smaller switches:

• Protects the CIRCUIT from overload or short circuit
• One MCB per circuit (lights, sockets, cooker, shower, etc.)
• Only that circuit loses power when it trips
• Labeled by circuit (e.g., "Downstairs sockets")

What To Check Before Resetting

1. Which circuit tripped?

• Look at fuse board—which switch is in "off" position?
• Check label (if board is labeled properly)
• If RCD tripped: multiple circuits will be affected
• If MCB tripped: only one circuit affected

2. What were you doing when it tripped?

• Plugged something in? (Faulty appliance)
• Turned kettle/heater on? (Overload)
• Using power tool? (Tripped RCD—common with drills/angle grinders)
• Nothing—just randomly tripped? (Fault in circuit)

3. Unplug everything on affected circuit:

• If sockets circuit tripped, unplug ALL appliances on that circuit
• Includes hidden ones (phone chargers behind bed, appliances in cupboards)
• This isolates faulty appliance

How To Reset Safely

Step-by-step reset procedure:

1. Unplug appliances on affected circuit (see above)
2. Turn off any lights on affected circuit (reduces load when resetting)
3. Reset the MCB that tripped (flip switch back to "on")
4. If RCD tripped: Turn all MCBs to "off" first, reset RCD, then turn MCBs back on one at a time
5. Check power restored (test a socket or light)
6. Plug appliances back in ONE AT A TIME to identify faulty one

Common Causes & What To Do

Cause 1: Faulty Appliance

Symptoms: Trips when you plug something in or turn it on

Fix: Unplug that appliance, don't use it. Get it PAT tested or replaced. Board won't trip again.

Cause 2: Overload

Symptoms: Trips when using multiple high-power items (kettle + heater + microwave simultaneously)

Fix: Don't use them all at once. Spread load across different circuits. Or get electrician to add circuit.

Cause 3: Water Ingress

Symptoms: Trips after rain, or in bathroom/kitchen circuits

Fix: Water got into socket or cable. Let it dry (24 hours), reset. If still trips, call electrician—internal short.

Cause 4: Rodent Damage

Symptoms: Random tripping, no obvious cause, old house, evidence of mice/rats

Fix: Rodents chewed cable insulation. Call electrician—can't DIY this. Needs cable replacement.

Cause 5: Old/Faulty RCD

Symptoms: Trips randomly, nothing plugged in, nuisance tripping

Fix: RCD worn out (they last 10-15 years). Needs replacement. £120-280.

When To Call Electrician (Don't DIY This)

Call immediately if:

• Trips twice in a row when reset (fault present)
• Burning smell from fuse board
• Sparking/arcing visible
• Fuse board hot to touch
• Can't identify which circuit tripped (unlabeled board)
• Multiple circuits affected but can't find cause
• Tripping at night randomly (suggests serious fault)

What Electrician Will Do

You call 0333 600 0990. Here's what happens:

1. Triage (5 minutes on phone):

• Which circuit tripped?
• How many times?
• What were you doing?
• Any burning smell/sparks?

2. Electrician arrival (90 minutes):

• NICEIC ID shown
• Testing equipment brought in

3. Fault diagnosis (30-60 minutes):

• Insulation resistance test: Checks cable insulation (finds water ingress, rodent damage)
• Continuity test: Checks cables intact (finds breaks, loose connections)
• RCD test: Checks RCD functioning properly (30mA trip current, trip time)
• Earth fault loop impedance: Safety check

4. Quote for repair:

• Diagnostic fee: £95 (absorbed if you proceed)
• Repair cost quoted including parts
• You approve or decline

5. Repair (30-90 minutes):

• Replace faulty RCD/MCB
• Or isolate damaged cable and repair
• Or replace damaged socket/accessory
• Test system, confirm fault cleared

Preventive Checks (Monthly)

Test your RCD:

1. Find "Test" button on RCD (yellow or black button)
2. Press it—RCD should trip immediately
3. Reset it
4. If it doesn't trip when tested: faulty RCD, get it replaced

Why test it? RCD might look fine but be faulty. Won't protect you from shock. Testing proves it works.

Action Checklist

1. ☐ Identify which switch tripped (RCD or MCB?)
2. ☐ Unplug all appliances on affected circuit
3. ☐ Reset switch (MCB directly, or RCD reset procedure)
4. ☐ Plug appliances back one at a time
5. ☐ If trips again: STOP, don't reset third time
6. ☐ Call electrician: 0333 600 0990

Need Emergency Electrician?

UK Power Response: 0333 600 0990

NICEIC electricians. 90-minute emergency response. Testing equipment in every van. Fault diagnosis £95 (absorbed into repair). Fixed pricing before work starts. Power restored same visit in 90% of cases.

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