Why do my electrics keep tripping? A checklist for London homes

Your electrics trip, you reset them, and an hour later they trip again. Before long you are going to the cupboard under the stairs several times a day. This is one of the most common reasons Londoners call an electrician. The good news is that you can often narrow down the cause yourself, safely, before anyone arrives.

First, know which switch tripped

Look at the front of your consumer unit. You do not need to open anything. There are two main kinds of switch.

Switch	What it does	What a trip usually means
RCD (residual current device), often with a T or test button	Cuts power when current leaks to earth	A faulty appliance, damp in a fitting, a damaged cable, or several small leaks adding up
MCB (miniature circuit breaker), small single switches	Cuts power to one circuit when too much current flows	Too many heavy appliances on one circuit, or a short circuit
RCBO, a single switch that does both	Protects one circuit from overload and leakage	Either of the above, but only on that circuit
Main switch	Turns everything off	It does not normally trip on its own; check if it was knocked

Write down which one tripped and what was happening at the time. That information saves an electrician a lot of searching.

The unplug and reset method

This is the safest first test you can do.

1. Switch off and unplug everything on the affected circuits. Include things you forget about: fridge freezer, washing machine, boiler plug, extension leads, chargers, outside lights.
2. Reset the switch that tripped.
3. If it stays on, plug in one appliance at a time, waiting a minute between each.
4. If it trips when one item goes in, leave that item unplugged and get it checked or replaced.
5. If it trips again with everything unplugged, the fault is in the fixed wiring or something wired in, such as a light, an immersion heater or an electric shower. Leave it off and call an electrician.

Do not reset more than a few times in a row. If it will not hold, stop.

Common causes we find

A faulty appliance. Kettles, washing machines, dishwashers, ovens and immersion heaters all use heating elements. When an element ages, it can start to leak current and trip the RCD. Our guide to oven, kettle and immersion heater trips goes further.

Water. Outside lights, garden sockets and bathroom fittings are the usual suspects. If trips get worse in wet weather, read electrics trip when it rains.

Overload. Several heaters, an air fryer and a kettle on the same kitchen circuit can trip an MCB, especially in winter.

Damaged cable. A nail or screw through a cable can cause a trip that starts after DIY.

Leakage adding up. Every appliance leaks a tiny amount of current. Put a lot of them on one RCD and the total can reach the trip level. This is common in older homes where many circuits share one RCD.

Timed loads. If trips happen at night or at the same time each day, something on a timer is a strong suspect. See RCD keeps tripping at night.

Why 1930s semis in Harrow trip more often

Harrow is a good example of how London’s housing affects its electrics. According to the VOA council tax stock of properties, 51.8% of homes in Harrow were built between 1919 and 1939, the highest share of the boroughs we cover. Rayners Lane, Kenton, Pinner and North Harrow are full of semis from that era.

Very few still have their original 1930s wiring. But many were rewired in the 1950s, 60s or 70s, and then extended. A typical semi might have:

• a later consumer unit added in front of older circuits
• a loft conversion or rear extension wired at a different time
• an old immersion heater in the airing cupboard
• outside lights and a garage fed by cable laid decades ago

Electrical Safety First notes that cables coated in black rubber were phased out in the 1960s. Where they survive, the insulation can crack and leak current to earth, which is exactly what an RCD detects.

Mixed era wiring is not dangerous in itself if it has been tested and is in good condition. But it does mean more possible places for a small fault, and more chance that adding a new RCD will reveal leakage that an old fuse box never noticed.

What an electrician will do

When you book our electrics keep tripping service, the visit usually involves:

1. Asking what tripped, when, and what was on.
2. Testing each circuit’s insulation, which measures how much current is leaking and where.
3. Testing the RCD to check it trips at the correct level and speed.
4. Isolating the faulty circuit or appliance and making it safe.
5. Explaining the fix and giving a price before any repair work starts.

If the board itself is the problem, or circuits are bundled on one RCD so a single fault takes out half the house, the electrician may suggest changes. That could mean moving circuits between RCDs, or a new consumer unit. Replacing a consumer unit is notifiable work under Part P of the Building Regulations. It must be done by a registered competent person who can self certify, or notified to building control. Ask to see the electrician’s scheme registration and check it on the scheme’s website.

What not to do

• Do not tape, wedge or hold a switch in the on position.
• Do not open the consumer unit cover.
• Do not swap fuses in an old fuse box for a bigger size.
• Do not keep resetting if you smell burning. Switch off at the main switch if safe and call for help.

If you are in Harrow or anywhere else in London and your electrics will not stay on, note what tripped, unplug and test, and call us when it still will not hold.