Earthing Rods for EV chargers

johnwicklover said:

Why is earthing rod needed in a TN-C-S System but not required in a TNS system?

Use of an earth electrode for TN-C-S is not mandatory.

There are restrictions for installation of EV charging equipment in installations with TN-C-S ("PME") systems in the UK, to protect people from a shock risk from the body of a car, due to certain faults in the LV supply network in the UK.

The options available to the installer of EV charging equipment, if there is a PME supply, according to BS 7671:2018+A2:2022 are:

• Use the option in BS 7671 Regulation 722.411.4.1 (ii) ... which permits an earth electrode to be used to limit touch voltage in a fault. Sadly, this requires an earth electrode resistance so low that it is only possible to achieve in certain installations (for example, where there is significant structural steelwork that can be used as the electrode).
• Use the option in BS 7671 Regulation 722.411.4.1 (iii), (iv) or (v) ... which permits fitting of a device to help detect and disconnect the vehicle from the supply (and supply earthing) if specific faults occur in the distribution network. Some of those devices may use a functional earth electrode a sufficient distance from all buried metalwork and exposed conductors connected to the PME earthing arrangement
• Provide a separate TT earthing arrangement for the EV charging equipment, which requires a consumer's earth electrode, and separation of earthing systems between TT and PME.
• Use an isolating transformer to supply the charging point as described in Annex A722 of BS 7671.

If the installation has a TN-S earthing arrangement, this problem is unlikely to exist, BUT if the supply is received at LV, then many distribution network operators in the UK may have converted part of the TN-S network to have combined neutral and earth cable, and there is no way for the installer to know.

If the earthing arrangement is TN-S, supplied from a transformer where it is guaranteed PME will not be supplied (e.g. a private HV to LV transformer), then the above precautions are not necessary.

johnwicklover said:

Could you have a earthing rod in a TNS system ?

Yes, supplementary earth electrodes can be used in TN-S systems - they can also be used in TN-C-S (PME) systems. Supplementary earth electrodes are recommended for TN systems by BS 7671, and would usually be necessary if the installation was a prosumer's electrical installation that included island mode operation.

johnwicklover said:

Why is earthing rod needed in a TN-C-S System but not required in a TNS system?

Use of an earth electrode for TN-C-S is not mandatory.

There are restrictions for installation of EV charging equipment in installations with TN-C-S ("PME") systems in the UK, to protect people from a shock risk from the body of a car, due to certain faults in the LV supply network in the UK.

The options available to the installer of EV charging equipment, if there is a PME supply, according to BS 7671:2018+A2:2022 are:

• Use the option in BS 7671 Regulation 722.411.4.1 (ii) ... which permits an earth electrode to be used to limit touch voltage in a fault. Sadly, this requires an earth electrode resistance so low that it is only possible to achieve in certain installations (for example, where there is significant structural steelwork that can be used as the electrode).
• Use the option in BS 7671 Regulation 722.411.4.1 (iii), (iv) or (v) ... which permits fitting of a device to help detect and disconnect the vehicle from the supply (and supply earthing) if specific faults occur in the distribution network. Some of those devices may use a functional earth electrode a sufficient distance from all buried metalwork and exposed conductors connected to the PME earthing arrangement
• Provide a separate TT earthing arrangement for the EV charging equipment, which requires a consumer's earth electrode, and separation of earthing systems between TT and PME.
• Use an isolating transformer to supply the charging point as described in Annex A722 of BS 7671.

If the installation has a TN-S earthing arrangement, this problem is unlikely to exist, BUT if the supply is received at LV, then many distribution network operators in the UK may have converted part of the TN-S network to have combined neutral and earth cable, and there is no way for the installer to know.

If the earthing arrangement is TN-S, supplied from a transformer where it is guaranteed PME will not be supplied (e.g. a private HV to LV transformer), then the above precautions are not necessary.

johnwicklover said:

Could you have a earthing rod in a TNS system ?

Yes, supplementary earth electrodes can be used in TN-S systems - they can also be used in TN-C-S (PME) systems. Supplementary earth electrodes are recommended for TN systems by BS 7671, and would usually be necessary if the installation was a prosumer's electrical installation that included island mode operation.