What is PME earthing failure and why is it so dangerous for my home – Advice from Electriman, North London Electricians

PME stands for Protective Multiple Earthing. It is the type of earthing system used in most UK homes, supplied by your electricity network operator. Understanding what can go wrong with it is important because the consequences are serious.

In a PME system, the earth connection in your home is provided by the same conductor that carries the neutral current back to the substation. This combined wire is called the PEN conductor. Under normal conditions this works safely, but if that shared conductor breaks or corrodes anywhere between the substation and your home, something very dangerous can happen.

When the PEN conductor fails, the neutral in your home loses its reference to true earth. Because appliances are still drawing current, the neutral voltage rises. All the metal pipework, radiators, sinks, taps, and anything else connected to the earthing system in your home can then sit at a voltage that is potentially fatal to touch. The outside of your washing machine, your boiler casing, your bathroom taps — all could become live.

Here is why this is so dangerous in practice:

1. It can happen without any fuses blowing or RCDs tripping.

2. The fault originates outside your property, so your own consumer unit gives you no protection against it.

3. Anyone touching earthed metalwork while standing on the ground or touching anything at true earth potential could receive a fatal shock.

What you can do safely as a homeowner is limit

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Electriman covers Mill Hill, Barnet, Finchley, Edgware, Enfield, Watford and surrounding areas. All work is Part P certified and fully insured.