An engineer friend recently recieved a request to look into the possibility of designing the installation for EV Charging points located on the top floor of a multi storey car park. The building is PME but begs the question of how can the EV Chargers be TT'd correctly ? IMO I would recommended chargers be installed on the ground floor if not only for ease of access (with the possibility of a disabled EV driver indiscrimanately having to park on the top floor) but also the TT spike installation would prove very difficult to install. My advice to him was to rethink the location but again wondered if anyone else had encountered this and how they approached the problem ?
Step back a moment. The only reason for TT is to avoid standing on the ground and getting a shock while in simultaneous contact with the ground and the car.
On any floor except the basement, unless the victim is a giraffe or has arms like Mr Tickle, this is a non issue, in fact it is safer if the car metalwork uses the PME earth, as the carpark light fittings and so forth will already be bonded to that, and this is all about reducing the voltage difference between accessible parts.
In the basement, an electrode is probably easier to arrange.
Won't the steel barriers to protect this occurrence be connected to some steelwork that is buried in the ground?
Assuming you mean prevent, rather than protect, any guard rails and fencing will only be driven into terra-firma one imagines on the bottom level. Any such barriers on the upper floors will presumably be bolted to tags cast into the concrete floor slabs. And if by some happenstance the whole thing is one big electrode, perhaps a steel walled and floored car park, rather than concrete, then well you have your electrode upstairs anyway.
In all cases, to minimise the shock risk, you need to bond the charger CPC and so the car metalworks to the same 'earth' as the accessible metalwork on that floor, if it is at a true terra-firma potential or not.
Agreed, top floor of multi-storey, provided of course the top floor is not at ground level, is really "indoor" - depending on how high we are talking, of course, lightning protection may be a more important consideration - installing charging points may well require a re-evaluation of the LPS on the top storey to ensure the charging equipment, and vehicles on charge, are adequately protected by the air termination and rooftop system.
