EV Charging TN-S Supply

Also you cannot have your TT earthing system being simultaneously accessible to another earthing system, see Regulation 411.3.1.1. So you may need to change Class 1 light fittings adjacent to Class 2 and enclose any nearby pipework.

Interestingly 411.3.1.1 only requires simultaneously accessible exposed-conductive-parts to be connected to the same earthing system - there's no such demand on extraneous-conductive-parts in that regulation - and normally no demand at all about extraneous-conductive-parts being isolated from the influence of a different earthing system. Which is all quite practical when you consider a typical TT installation which may share a metallic water pipe with next door who uses PME. Common sense might indeed suggest that you would want to avoid the influence of two different earthing systems being within reach of each other - but the regulations don't seem to make that a specific requirement - indeed 714.411.3.1.2 seems to reduce the normal requirements for bonding extraneous-conductive-parts for outdoor systems (including highway power supplies & street furniture) - which arguably EVSE might fall under as well as section 722.


In terms of reducing shock, the aim surely should be to try and keep the EVSE's earth at a similar potential as possible to the ground on which the vehicle will be standing - which isn't necessarily the general mass of the earth. Consider where the installation's metallic water supply pipe runs directly underneath the drive (probably not unusual) - in such cases having the TT electrode moderately close to the pipe so that its potential varied in a similar way to the ground surface would provide better safety than having it a greater distance away to avoid such influence.  A 'ditch tape' electrode around the perimeter of the parking space, regardless of the influence of any other buried metalwork, might be a far more effective approach than attempting isolation from other earthing influences (installation practicalities notwithstanding of course).


722.411.4.1 has changed quite recently - I'm not sure its evolution is yet complete.


  - Andy.

Also you cannot have your TT earthing system being simultaneously accessible to another earthing system, see Regulation 411.3.1.1. So you may need to change Class 1 light fittings adjacent to Class 2 and enclose any nearby pipework.

Interestingly 411.3.1.1 only requires simultaneously accessible exposed-conductive-parts to be connected to the same earthing system - there's no such demand on extraneous-conductive-parts in that regulation - and normally no demand at all about extraneous-conductive-parts being isolated from the influence of a different earthing system. Which is all quite practical when you consider a typical TT installation which may share a metallic water pipe with next door who uses PME. Common sense might indeed suggest that you would want to avoid the influence of two different earthing systems being within reach of each other - but the regulations don't seem to make that a specific requirement - indeed 714.411.3.1.2 seems to reduce the normal requirements for bonding extraneous-conductive-parts for outdoor systems (including highway power supplies & street furniture) - which arguably EVSE might fall under as well as section 722.


In terms of reducing shock, the aim surely should be to try and keep the EVSE's earth at a similar potential as possible to the ground on which the vehicle will be standing - which isn't necessarily the general mass of the earth. Consider where the installation's metallic water supply pipe runs directly underneath the drive (probably not unusual) - in such cases having the TT electrode moderately close to the pipe so that its potential varied in a similar way to the ground surface would provide better safety than having it a greater distance away to avoid such influence.  A 'ditch tape' electrode around the perimeter of the parking space, regardless of the influence of any other buried metalwork, might be a far more effective approach than attempting isolation from other earthing influences (installation practicalities notwithstanding of course).


722.411.4.1 has changed quite recently - I'm not sure its evolution is yet complete.


  - Andy.