Your RCD keeps tripping: the causes, and the one thing not to do

The RCD, the device in your board with a test button on it, is the only component in the house whose job is to save a life. The MCB protects the cable so it does not start a fire; the RCD protects you so a shock does not kill you. When it keeps tripping, it is telling you something.

# What it actually does

It compares the current going out with the current coming back. In a healthy circuit, every amp that leaves on the line returns on the neutral. If some of it returns by another path, through your body or through damp inside a wall to earth, the device sees the imbalance and disconnects in a fraction of a second. The standard threshold is 30 mA, about thirty thousandths of an amp.

# The usual causes, in order of how often they turn up

• Damp: the most common cause in Gilan. Water in an outdoor socket, a junction box in the yard, or a wall that has taken moisture.
• A faulty appliance: water heaters, washing machines, water pumps and air conditioners lead the field.
• Perished cable insulation: in older buildings the insulation dries and cracks over time.
• Cumulative leakage: several appliances each leaking a little, adding up past the threshold.
• A neutral-to-earth connection: a wiring error, usually introduced during a repair or alteration.
• A faulty RCD itself: possible, but the least likely. It is the last thing to suspect, not the first.

# Narrowing it down to one circuit yourself

This is safe to do, because protection stays in place throughout and all you are touching is the switches.

1. Switch off every MCB downstream of the RCD.
2. Reset the RCD. If it trips with everything off, the fault is in the device or the wiring ahead of the MCBs: stop here and call an electrician.
3. If it holds, switch the MCBs back on one at a time, pausing between each.
4. Whichever one trips it is your suspect circuit. Leave that one off and bring the rest back on.
5. On the suspect circuit, unplug everything connected to it, then switch it back on.
6. If it now holds with the circuit empty, the fault is in an appliance: plug them back one by one until it trips.
7. If it trips even with nothing plugged in, the fault is in the fixed wiring and needs an insulation tester.

# The one thing never to do

Do not bypass the RCD or swap it for an ordinary breaker. It happens depressingly often: the device keeps tripping, somebody "fixes the problem", and it never trips again. But the leakage is still there. All that was removed is the thing that was going to stop an electrocution.

Earth leakage does not heal. The damp that trips the device today provides the same path tomorrow for current through somebody who touches a tap and a metal appliance at the same moment.

# Take the test button seriously

There is a test button on the RCD. Press it once a month; the device should trip immediately. If it does not, it is not protecting you and it needs replacing. The test takes ten seconds and it is the only way to know the device still works.

If the fault turns out to be in the fixed wiring, or the device fails its test, call for an insulation and earth test in Gurab Zarmikh, Soumeh Sara and the surrounding area.