Why does my AFDD keep tripping?

Helpful video reference. We use eFIXX's video "REVEALED: The Secrets of an Arc Fault Detection Device AFDD" as the video reference here. eFIXX is a UK electrical training platform covering industry topics for tradespeople and homeowners. Their explanation of how an AFDD differs from an RCD and MCB is one of the clearest available, and it is worth watching before you start fault-finding so you understand what you are dealing with.

1. Check which device has actually tripped

Open the consumer unit door and look at all the breakers. The terminology gets confusing because an AFDD is often fitted as a combined AFDD/MCB unit, and many boards also have a main switch RCD or RCBO devices.

There are three different devices that could have tripped, each with a different meaning:

• MCB only - the circuit is overloaded or there is a short circuit. This is not AFDD territory; you have too many appliances on the circuit or a dead short somewhere.
• RCD or RCBO - current is leaking to earth. A faulty appliance or a wiring fault with an earth path. Nothing to do with arcing.
• AFDD - the device has detected an arc fault signature. This is what the rest of this guide addresses.

The AFDD reset button or lever will be in the tripped position. On most combined AFDD/MCB units there is also a separate test button, usually marked T.

2. Test the AFDD itself

With the circuit live and reset, press the T (test) button on the AFDD. It should trip within a second. If it does not trip, the AFDD may be faulty and should be replaced by an electrician.

If it trips correctly on test, reset it. If it holds and stays on - note whether it then trips again when you reconnect loads (step 4), or whether it trips immediately on reset even with nothing connected (step 7).

3. Remove all loads from the circuit

Before resetting the AFDD again, switch off or unplug every appliance on the circuit at the wall or socket. For a socket ring circuit this means unplugging everything. For a lighting circuit it means switching off all switches and removing any smart-switch loads that stay drawing power.

Now reset the AFDD. Does it hold? If yes, a connected load was causing the trip - move to step 4. If it trips immediately with nothing connected - go to step 7.

4. Reconnect loads one at a time

Plug in and switch on appliances one at a time, waiting about a minute between each. The AFDD will trip when you reconnect the problem load. That is your suspect.

Common culprits for AFDD trips include:

• Vacuum cleaners with worn carbon brushes in the motor (brush arcing triggers AFDD detection)
• Appliances with faulty leads - frayed flex, cracked insulation, or plug pins that move
• LED dimmer circuits where the dimmer creates electrical noise that the AFDD misreads as an arc
• Extension leads with poor contact in the sockets
• Power tools with worn motor brushes

Once you have identified the load, take it out of use until it has been repaired or replaced. An appliance that triggers an AFDD is either genuinely failing or generating enough electrical noise to suggest it is on its way out.

5. Inspect cables and appliance leads

For any appliance that triggered a trip, inspect the flex carefully from plug to appliance. Look for cuts, kinks, scorch marks, or chewed sections. Check the plug itself - are the pins loose? Is there discolouration inside the plug body? A scorched or melted plug interior is a sign that arcing has already been occurring for some time.

Check the socket the appliance was using. Discolouration around the socket holes, burning smell, or visible blackening around the live or neutral hole suggests arcing at the socket contact. Do not continue using that socket - call an electrician to replace it.

6. Check for intermittent connections

Loose connections are a major source of arcing. With the circuit isolated and dead (confirmed with a voltage tester), check any accessible connections on the circuit:

• Plug pins that move in the plug body
• Extension lead sockets that feel loose
• Any socket that rocks slightly in its back box

If the AFDD trips when you wiggle a lead or move an appliance slightly, the arcing is at a mechanical connection - the plug, the socket, or the flex where it enters the appliance body. That specific item needs repair or replacement.

7. AFDD trips with no loads connected

If you reach this step - the AFDD trips with the circuit completely unloaded - there is almost certainly a fault in the fixed wiring. Possibilities include:

• A nail or screw driven through a cable behind a wall or under a floor
• A damaged junction box connection that has deteriorated over time
• Water ingress at a back box or fitting
• Cable insulation that has broken down through age or heat damage

Do not continue resetting the device. Leave the circuit isolated and call a qualified electrician. Finding a hidden wiring fault requires testing equipment and the ability to open walls or floors safely. It is not a DIY task.

When to call us

Richard covers fault-finding in Sandwich, Deal, Dover and the surrounding east Kent area. If your AFDD trips with no obvious cause, or you have found a damaged socket or suspect wiring fault, he can diagnose the problem with proper test equipment and fix it correctly. Work inside consumer units and fault repairs in fixed wiring are all notifiable under Part P - Richard is registered to certify and notify this work.