In a commonly used earthing arrangement in the UK known as T-N-C-S (Terra Neutral Combined Separate) or also known as ”PME” there is a PEN conductor.
PEN = Protective Earthing Neutral.
Essentially, the supply to the property is along 2 conductors, the Line (previously known as “Live”) and the PEN conductor which acts as the neutral and earth in 1.
Once it enters the property it is then separated into individual neutral and earthing conductors where they continue to act as separate conductors throughout the installation.
When it is working correctly then yes, it is safe. However, if the PEN conductor fails on the local power network (break down of cable joint in street, damaged cable, water ingress etc) then we have a major problem and here’s why;
The line conductor will still be supplying a voltage of circa 230 volts, but it will no longer have a return path via the neutral which it needs to complete a circuit.
That means any metallic objects within the home will now have a potential difference to true earth – anyone coming into contact with these surfaces will make the circuit to true earth (the ground below their feet) and the electricity will flow through them completing the circuit – which depending on how conductive they are could result in a tingle, through to a severe shock with live threatening injuries.
For example, in the home this would include water pipes, sinks, boilers, potentially any water too.
Outside the home anyone sitting in hot tub (without additional measures in place) would likely
receive a shock as they make the circuit when they leave the water and touch down to ground (real earth) and given the moisture of the body and potential for wet ground conditions this would be an ideal condition for an electric shock.
The same can occur with an Electric vehicle (EV), whilst it is charging outside if there is a PEN fault then there is a possibility of the bodywork becoming live – now as the tyres are a good insulator the flow of current will not go anywhere until the circuit is made, potentially by a person touching the bodywork and being on contact with the ground at the same time.
With vehicle bodywork being predominantly metallic, this is a major concern under PEN fault condition.
This is why PEN fault protection is required is required for EV chargers, either a standalone unit that is fitted downstream of the car charger, or an integral PE fault protection device within the EV charger itself.
Good question – it monitors the voltage between Line and Earth and will disconnect the supply if it detects these values are out of range.
If you have either a T-N-C-S or a T-N-S earthing arrangement, then yes you will – though at the time of writing this most EV chargers have an integrated PEN fault detection system so there isn’t usually a need to have an external unit.
Yes, they are unfortunately. Here’s a quote from an article that featured recently in the IET (Institute of Engineering Technology).
“Reports of broken PEN conductors increased from 57 in 2003 to 474 reports last year (2021) according to a Freedom of Information (FOI) request. As incidents are often not reported, the real figure is likely to be much higher and each incident can affect fifty properties, meaning tens of thousands of properties are likely at risk in the UK.”
Given the number of EV chargers on the network and their combined loading – I suspect things will get worse before they get better.
