Earthing Electric Vehicle Charge Points,
and why it is so important

Most UK households have a PME supply (protective multiple earth) This is a very reliable method of providing electrical installations with an earth connection.

PME (TNCS) is the most common form of earthing provided at new installations and utilises a single conductor for the neutral and earthing functions (PEN) with an earth terminal derived from the neutral cable. The danger arises if there is an open PEN conductor within the network. This can lead to an electric shock if any metallic parts, including gas pipework and any bonded appliance, were touched by a person in simultaneous contact with the general mass of Earth
Unfortunately, MCBs and RCDs currently used DO NOT detect this fault and DO NOT offer any protection
Because of this the IET Wiring Regulations BS:7671 2018 Amendment 1 2020, states that a PME earthing facility shall not be used as means of earthing for the protective conductor contact of a charging point located outdoors or that might reasonably be expected to be used to charge a vehicle located outdoors.
Unless one of the following methods is used

o The charge point forms part of a three-phase installation where all of the demand including the charge point/s are balanced over all of the available phases –
This is almost impossible to achieve as loads on each phase will vary continually with equipment connected being on or off throughout the day

o The car charging installation includes an Earth electrode of sufficient resistance to ensure the rise of earth potential will be limited to a maximum of 70 V rms during a broken neutral event –
This is only an acceptable solution if you can guarantee no simultaneous contact with the PME earth

o Protection of electric shock is provided by a device which disconnects the charging point/s from the live conductors of the supply and the protective earth within 5 seconds in the event of a broken neutral regulation 543.3.3.101(ii). -
This is the ideal solution as it allows connection to a PME earth without having to meet the strict criteria of the above methods.



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An RCD will not provide any protection against these effects

So to prevent anyone within the building being subjected to this voltage protective bonding is required for all extraneous conductive parts
  • Incoming metal water pipes, gas pipes and other incoming metal pipes
  • Metal central heating pipes and ducting
  • Metal Structural parts of the building

However, this bonding will NOT protect people outside the building who are simultaneously in contact between conductive parts connected to the PME earth – eg an electric vehicle being charged AND true earth – eg metal work connected to the ground but not connected to the main earthing terminal (MET) of the building
Because of this there are very specific regulations regarding the installation of an Electric Vehicle Charge Point IF the charge point is located outdoors or IF located indoors might be reasonably be expected to be used to charge a vehicle outdoors.

So, if your charging equipment is located indoors – an integral garage - with a tethered non-extending cable that only allows the vehicle to be charged inside, then the PME earth can be used without the need for a separate earth pit.

However, if the vehicle is to be charged outside then a separate TT system should be adopted. The charge equipment must be located where there is no risk of simultaneous contact with metal parts connected to the PME earthing system.

"The final circuit supplying an electric vehicle charging point shall not include a PEN conductor" (combined neutral and protective conductor or TNCS system)
Regulation 722.312.2.1 Electrical installation requirements BS7671:2018

As most properties in the UK adopt this system of electrical protection. You will therefore usually have to have a separate earth pit installed or an O PEN LNE disconnector

There are 3 types of earthing arrangements used
in UK households. Which one do you have?

TT - Identifying a TT system

NO green and yellow cable or green cable or wire mesh connected to the black cable coming into your property just below the main fuse. An earth pit or rod will be located outside your property usually near the main fuse

If your property has a TT earthing arangement you will not require a seperate earth

TNCS - Identifying a TNCS circuit

A green and yellow cable or green cable coming out of the main fuse

If your property has a TNCS (PME) earthing arrangement you will usually require a seperate earth.

TNS - Identifying a TNS system

A green and yellow cable or green cable or wire mesh connected to the black cable coming into your property just below the main fuse

If your property has a TNS earthing arrangement you will usually require a separate Earth, unless the network supplier can guarantee the supply will not be upgraded to a TNCS System
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