How to Reset a Tripped RCD and Find the Faulty Circuit

Many houses have a separate RCD which protects a bank of circuits. I think case a fault on one circuit will mean that a whole section of circuits will all go off. 

How to Reset a Tripped RCD and Find the Faulty Circuit

It’s a situation we’ve all experienced: suddenly, the lights go out, or your appliances cut off. Usually, this means your RCD (Residual Current Device) has tripped in your consumer unit (fuse box).

An RCD is a crucial safety device designed to instantly switch off the electricity if it detects a fault, preventing dangerous electrical shocks and potential fires.

If your power has just gone off, don't panic. Follow this simple guide to safely reset your RCD and identify exactly which circuit or appliance is causing the problem.

Step 1: Locate Your Consumer Unit

First, find your consumer unit (fuse box). They are typically located in hallways, utility rooms, under the stairs, or in a garage.

When you open the cover, you will see a row of switches. The RCD is usually a wider switch with a "Test" or "T" button next to it. If it has tripped, the switch will be in the OFF position (pointing downwards).

Step 2: The Quick Reset

Sometimes, an RCD trips due to a temporary surge (like a lightbulb blowing).

Push the tripped RCD switch firmly back up to the ON position.

If it stays up and the power returns: It was likely a minor, one-off surge. You’re good to go!

If it instantly clicks back down: Do not force it. This means there is an active fault on one of your circuits. Move to Step 3.

Step 3: How to Identify the Faulty Circuit

If the RCD refuses to stay up, you need to isolate your individual circuits to find the culprit. Follow these steps precisely:

1. Turn OFF all MCBs (Circuit Breakers)
   Look at the row of smaller switches (called MCBs) that are protected by that RCD. Flip every single one of them down to the OFF position.
2. Reset the RCD With all the individual circuits turned off, try flipping the main RCD switch back up to the ON position. Because no electricity is flowing to the circuits yet, it should now stay up.
3. Switch the MCBs Back On, One by One

Now, turn the smaller circuit switches (upstairs lights, downstairs sockets, cooker, etc.) back ON, one at a time.

• Watch and listen closely as you flip each switch.
• The Moment it Trips: When you flip a specific switch and the main RCD instantly trips back to OFF again, you have found the problem circuit!

Step 4: What to Do Once You Find the Faulty Circuit

Now that you know which circuit is causing the issue (for example, "Downstairs Sockets"), you can narrow down the cause.

1. Leave that specific faulty MCB switch OFF.
2. Reset your main RCD and turn all the other working MCBs back ON. This ensures you have power back to the rest of your house.
3. Unplug everything on the faulty circuit: Go around the area controlled by the broken circuit and unplug every single appliance (kettle, toaster, fridge, washing machine, etc.).
4. Test the circuit again: Go back to the consumer unit and try flipping the faulty MCB switch to ON.
   • If it stays up: The fault is being caused by one of your appliances. Plug them back in one by one until the power trips again—the last appliance you plugged in is the broken one!
   • If it trips immediately even with everything unplugged: The issue is likely a fault with the hardwiring, a socket itself, or water ingress. Do not attempt to fix this yourself.