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

PME stands for Protective Multiple Earthing. It is the most common type of earthing system used in UK homes, supplied by your electricity network operator such as UK Power Networks, Northern Powergrid or Western Power Distribution. Under normal conditions it works safely and reliably, but a specific type of failure can make it extremely dangerous.

How PME normally works

In a PME system, your home's earth connection is tied to the neutral conductor of the electricity supply network. The network is connected to the ground at multiple points along the street, which keeps the earth in your home at a safe zero volts. This is why the system is called Protective Multiple Earthing.

What goes wrong during a PME failure

If the shared neutral conductor breaks or corrodes somewhere upstream, perhaps in the street cable or at a joint in the network, your home loses its connection to those multiple earth points. The neutral in your installation, which is now also your earth, is no longer anchored at zero volts. Load currents from neighbouring properties can push that conductor to a voltage that may reach 110 volts or more relative to true ground. All metalwork in your home that is connected to the earthing system, including taps, radiators, boiler pipework, sinks, appliances and socket earth pins, can become live at that dangerous voltage.

Why it is so dangerous

A person touching an earthed metal surface while standing on the ground,

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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.