Electrics after a leak or flood

Electrical Safety First advises switching off at the consumer unit only if it is safe to do so, getting a registered electrician if there is any sign of water inside the consumer unit or of arcing or overheating, and not using mains powered appliances until you are told it is safe. Keep away from any exposed wiring, as it may still be live.

If the leak is coming from a pipe in your home, turn off the water at the stop tap. If it is coming from the flat above, tell your neighbour or the managing agent straight away.

57% of London homes are flats, rising to 72% in Wandsworth and 82% in Hackney, according to the Valuation Office Agency. A washing machine hose or overflowing bath upstairs often comes down through ceiling roses and light switches, because cable holes are the easiest path.

Who pays depends on the cause and your lease. The flat owner usually looks after the wiring inside their flat, and the freeholder or managing agent looks after communal parts. Tell your insurer early and keep photos. Our advice on a leak from the flat above goes through it.

London has seen how fast this can happen. Two flash floods on 12 and 25 July 2021 affected 24 boroughs and more than 2,000 properties, including homes and Underground stations, according to the Environment Agency. Basement flats and ground floors with sockets near the floor were among the worst hit.

After a flood, every circuit that was under water needs testing, and corroded sockets, floor boxes and consumer units are usually replaced. Electrical Safety First suggests asking whether new sockets and the consumer unit can be raised above any expected flood level. Raising sockets or moving a board is notifiable work in some cases, so it needs a registered installer or a building control notice.

Water does not always cause an instant fault. A wet ceiling rose may work for a day, then trip the lights when the water reaches a joint. That is why the advice is to keep the affected circuit off until it has been tested, even if it seems fine.

The main test is insulation resistance. It shows whether current can leak from the cables to earth. Wet insulation gives a low reading. As things dry, the reading rises. Some circuits recover once dry. Others do not, especially if dirty flood water got into fittings, or if the cable was already old.

Fittings that have been under water, or filled with water from above, are usually replaced, because dirt and corrosion stay inside. Sockets fitted low on walls in basements and ground floor flats are the ones most often lost in a flood. When they are replaced, it is worth asking whether they can go higher. The consumer unit can sometimes be moved up as part of a replacement too.

Keep the electrician's report. Insurers often ask for it, and it shows any later buyer or tenant that the electrics were checked after the water. Our post on electrics after a flash flood covers what London learned in 2021.