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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
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    part of the problem is that the regs make no distinction between the case of (extraneous) conductive parts that are lightly earthed like the fence post, or even an earth electrode, where yes, it is grounded, but via significant electrode resistance, such that current is limited, and a person holding it is probably no more connected to earth and at risk than if the metal was not there, but they were barefoot on the ground.


    and the other case of parts that are solidly connected to the neutral or earth elsewhere, and can carry a large current,  potentially enough to start a fire, and really are part of the earthing system, and need either solidly bonding or keepoing out of reach.


    A  palms of hand contact with say a galvanised handrail connected to a PME earth at a bus stop, is quite different shock proposition to a similar looking rail 'planted'  on concrete pads on the earth, even if the footings are buried, and mud comes up round the bottoms of the bare metal for a bit.

    I am reminded of the railway fence dilemma to bond or not to bond that came up last year. Sadly I do not think we know the conclusion the OP reached on that one.
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  • 0
    part of the problem is that the regs make no distinction between the case of (extraneous) conductive parts that are lightly earthed like the fence post, or even an earth electrode, where yes, it is grounded, but via significant electrode resistance, such that current is limited, and a person holding it is probably no more connected to earth and at risk than if the metal was not there, but they were barefoot on the ground.


    and the other case of parts that are solidly connected to the neutral or earth elsewhere, and can carry a large current,  potentially enough to start a fire, and really are part of the earthing system, and need either solidly bonding or keepoing out of reach.


    A  palms of hand contact with say a galvanised handrail connected to a PME earth at a bus stop, is quite different shock proposition to a similar looking rail 'planted'  on concrete pads on the earth, even if the footings are buried, and mud comes up round the bottoms of the bare metal for a bit.

    I am reminded of the railway fence dilemma to bond or not to bond that came up last year. Sadly I do not think we know the conclusion the OP reached on that one.
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