I mentioned in another post that I would contact HSE regarding any issues reported to them arising from loss of neutral and EV charging points. They have responded and confirmed that there has been no incident reported to them. However, they were made aware of a small number of situations that were a result of poor or no load management. I should point out that this is HSE in Northern Ireland.
Indeed, PME is the worst of all worlds. The safety conductor should NEVER carry power in normal usage. It's just a copout due to years of little to no maintenance
6.1 In accordance with The IET Wiring Regulations (Eighteenth Edition) BS 7671 and ST:TP21E, “ A PME earthing facility shall not be used as the means of earthing for the protective conductor contact of a charging point located outdoors or that might reasonably be expected to be used to Charging a Vehicle located outdoors unless one of the following methods is used” :-
The charging point forms part of a three phase installation where all of the demand including the Charging point/s are balanced over all of the available phases.
The car charging installation includes an earth electrode of sufficient resistance to ensure that the Rise of Earth Potential (ROEP) will be limited to a maximum of 70 volts during a broken neutral event.
Protection against Electric shock is provided by a device which disconnects the charging point from the live conductors of the supply and from protective earth within 5 s in the event of a broken neutral.
6.3 TT earthing arrangements shall be utilised by Electric Vehicle Charging Points that do not meet the PME requirements specified in clause 6.1.
As I previously mentioned, it is the company who set the standard for distribution utilisation in their own area. Only the local DNO can understand the capability of their network, which incidentally exceeds far and beyond the limitations of a simple guide book, published mainly for small domestic/commercial installations
As regards, "In accordance with....." Western are being polite! they want the guide book to feel loved, to be wanted in the industry!
The wording in the post from Sparkingchip is years old, set by UKPN around 10 years ago. the wiring regs hadnt caught up then, but it started to use the wording a couple of years later, which is the pattern. The best example, probably was the creation of 16th ed wiring regulations, All of a sudden a whole raft of "special locations" appeared, The common or garden bathroom, farms, building sites, even a street bollard now needed special attention. Marinas, caravans, oh dear! Outside in the real world the former electricity boards had of course been guiding electricians since the 60s with their supply issues for all electrical installations. Before that, simple water pipe/rod earthing sufficed, but the area boards took the industry in to the great new world of PME networks, new cabling enabling Electricians throughout the land to achieve disconnection times unheard of previously. Voltage operated ELCBs, steel fuse boxes without an effective earth, all left behind thanks to the great supply industry engineers. Time moves on, and in recent years the London guys have been involved in projects bigger than before, Terminal 5, The Shard, new football stadiums and many new tower blocks. The EV strategy is in place for the area and the company will continue to increase its load capability accordingly.
All EVCP’s in the public highway must be connected to a TT earthing system.
A PME earth terminal shall not be used (the supply and installation of earthing system and protection is the responsibility of the EVCP installer) as set out in section 6.2 of EDS 08 5050
Yet UKPN, as in you, appear to be telling us that using TNCS for an EV charger is perfectly fine.
Perhaps you can reference guidance from UKPN, the DNO, as to how to safely install an EV charger with TNCS earthing.
I am never confused, ( at work)!!! I cannot speak though for other DNOs,and different areas have different policies. North Norfolk may have different policies to central London. LPN, London power networks, SPN, South power networks and EPN, Eastern power networks have slightly different policies because of historical issues. EV chargers on the public highway, ( and certain other areas) would not be offered a PME terminal.
On consumers property, PME is allowed though unlikely, as the resistance of a rod would be virtually impossible to obtain, so we are looking at TT or 1/1 transformer. Apparently there is a new "gadget" which disconnects the L/N/E but I have not looked into it, I cant see how that would work, normal voltage drop on the network would carry over to the car body and people would get tingles. But I am open to stand corrected on that.
So, in answer to your question, PME on the driveway, depending on loadings/resistance
I only found one variation between the IET guidance and the DNO guidance.
The IET are saying that there should be 10 metres of separation between the consumers TT electrode and parts of the DNO TNCS-PME network, including buried service cables and extraneous metalwork, however Western Power and other DNOs say this can be reduced to 3.6 metres for single phase and 0.3 metres for balanced three phase, which makes it a lot easier to install charging points alongside a public highway.
