What is PME earthing failure and why is it so dangerous?

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, or touching two earthed metal surfaces at slightly different voltages, can receive a fatal electric shock. Residual current devices will not protect against this because the fault is on the supply side, upstream of your consumer unit. What you should do if you suspect a problem You should treat any unexplained tingling sensation from taps or metalwork as an urgent warning sign. Do not touch any metalwork in the property. Do not enter or remain in the property if you can avoid it. Call your Distribution Network Operator on their emergency number, which is 105 from any phone in the UK, available 24 hours a day. Do not attempt to investigate or repair the fault yourself. This is not a job for an electrician working inside your property. The fault lies in the supply network and must be made safe by the network operator before any internal work is carried out.