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EVs, Street furniture, PME and TT configurations

Former Community Member
Former Community Member
Good afternoon all,


I'm part of one of the teams installing the EV charging points around London and we keep running into the same situations and problems when going through the site selection process - proximity of other electrified street furniture to the units we are installing (as well as potentially plugged in cars which is measured to the edge of the parking bay.)

Regs say that any EV installation cannot be connected to a PME system and must be converted to a TT in case of a damaged/faulty PEN conductor. Naturally if you're converting something to a TT system and not using the DNO TN-C-S earthing arrangement, there must be a reasonable distance between the TT and any other TN-C or TN-C-S systems (2m or so is reasonable).

If there were other services in the vicinity but can be proven that these have also been converted to TT and are 100% confirmed to not be using the DNO earth, would it be reasonable to say that the requirement for the 2m distance can be reduced or ignored completely? Another thought I've had is to bond the cabinets together - being on the same type of system, it makes logical sense that this would in turn reduce the Ze and improve disconnection times, both units have their methods of ADS and incorporate an RCD/RCBO of a 61008 or 61009 standard respectively.


Any other thoughts or ideas would be much appreciated as I try and figure a workaround for this issue. I understand this could work for smaller cabinets and for individual supplies, and not necessarily for street lighting which might not be adequately equipped for being converted to TT (bit of a bigger job to start installing RCDs and then giving a minor works cert etc.).
Parents
  • 0
    If the total load downstream of the PEN that breaks is only something small like a lamp post and the load is hundreds of watts or less, I agree, the light will keep working dimly as a sort of single wire earth return, assuming a respectable electrode resistance,  and the touch and step voltages will be significant, but probably safe enough to persist for days or weeks until the fault is noticed.. For higher current single load loads, like the car charger,  or just a break further back down the chain, it is not clear that this works well enough. 


    This is where ADS in the form of the magic all-pole breaking (including the CPC ) lost neutral detector is needed, either with phase/ neutral variation detector, or using a low current, high Z pilot earth electrode to allow some sensing.


    In the mean time free draining ballast spread on the ground around he charger and vehicle will reduce the danger from step voltage, in two ways, once because it raises the contact resistance, and secondly because the stones are so darn uncomfortable, no-one in bare feet will stand on them if they can possibly avoid it.


    I sense that the advice will need to change as it is probably becoming unworkable right now.
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  • 0
    If the total load downstream of the PEN that breaks is only something small like a lamp post and the load is hundreds of watts or less, I agree, the light will keep working dimly as a sort of single wire earth return, assuming a respectable electrode resistance,  and the touch and step voltages will be significant, but probably safe enough to persist for days or weeks until the fault is noticed.. For higher current single load loads, like the car charger,  or just a break further back down the chain, it is not clear that this works well enough. 


    This is where ADS in the form of the magic all-pole breaking (including the CPC ) lost neutral detector is needed, either with phase/ neutral variation detector, or using a low current, high Z pilot earth electrode to allow some sensing.


    In the mean time free draining ballast spread on the ground around he charger and vehicle will reduce the danger from step voltage, in two ways, once because it raises the contact resistance, and secondly because the stones are so darn uncomfortable, no-one in bare feet will stand on them if they can possibly avoid it.


    I sense that the advice will need to change as it is probably becoming unworkable right now.
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