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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.).
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    Yes, you can't legislate for everything, the situation is in a right pickle. There will be other areas where for one reason or another soil resistivity is far lower than average too.


    To be honest, I'm most worried in all this how electricians are supposed to work out what's going on with other services ... in many places, no-one knows where they are. And to boot, none of it is really directly related to the consumer's installation, it's all outside influences driving a range of, what some may say are, less-than-satisfactory solutions at the moment.



    Indeed. I've a feeling that all this trying to create an "equipotential zone" out of doors is rather letting the perfect become the enemy of the good.


    There's a long standing exception to bonding extraneous-conductive-parts within reach of lighting columns etc. (currently 714.411.3.1.2 but has been there in a similar form for decades I'm sure) - which doesn't seem have have caused any problems whatsoever in practice. At the moment I'm thinking that exposed-conductive-parts of a TT system - especially ones that'll probably easily comply with RA x IΔn ≤ 25V (let alone 50V) and satisfies 0.2s disconnection time and 40ms @ 150mA) doesn't pose any more of a hazard w.r.t. an adjacent PME's lighting column than any other bit of metalwork that's in contact with the general mass of the earth (such as a fence or cycle stand) - or indeed the ground surface itself (which usually seems to get overlooked in equipotential zone discussions). In these cases the TT'd item won't be at a hazards voltage above true earth for a hazardous duration - so it seems to me we should be able to treat it as simple extraneous-conductive-part as far as neighbouring systems are concerned - and so apply 714.411.3.1.2 (even if the EVSE happened to be installed after the lamppost). The hazard posed by the PME lamppost is what it already is and isn't made unacceptable by installing another bit of metalwork nearby (whether a fence or a cycle stand or a TT'd EVSE).


    Indeed I might question how "conductive" to touch all these items are in practice - steel lighting columns are usually heavily painted, likewise car bodywork, car door handles and charging connectors tend to be plastic, outdoor footwear usually insulating, posts for roadsigns plastic coated and so on. Nothing you'd want to rely on in lieu of basic insulation of course, but nevertheless they must reduce the chances of a shock in practice. What is the real probability of someone coming to harm even with a broken CNE?


        - Andy.
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  • 0

    Yes, you can't legislate for everything, the situation is in a right pickle. There will be other areas where for one reason or another soil resistivity is far lower than average too.


    To be honest, I'm most worried in all this how electricians are supposed to work out what's going on with other services ... in many places, no-one knows where they are. And to boot, none of it is really directly related to the consumer's installation, it's all outside influences driving a range of, what some may say are, less-than-satisfactory solutions at the moment.



    Indeed. I've a feeling that all this trying to create an "equipotential zone" out of doors is rather letting the perfect become the enemy of the good.


    There's a long standing exception to bonding extraneous-conductive-parts within reach of lighting columns etc. (currently 714.411.3.1.2 but has been there in a similar form for decades I'm sure) - which doesn't seem have have caused any problems whatsoever in practice. At the moment I'm thinking that exposed-conductive-parts of a TT system - especially ones that'll probably easily comply with RA x IΔn ≤ 25V (let alone 50V) and satisfies 0.2s disconnection time and 40ms @ 150mA) doesn't pose any more of a hazard w.r.t. an adjacent PME's lighting column than any other bit of metalwork that's in contact with the general mass of the earth (such as a fence or cycle stand) - or indeed the ground surface itself (which usually seems to get overlooked in equipotential zone discussions). In these cases the TT'd item won't be at a hazards voltage above true earth for a hazardous duration - so it seems to me we should be able to treat it as simple extraneous-conductive-part as far as neighbouring systems are concerned - and so apply 714.411.3.1.2 (even if the EVSE happened to be installed after the lamppost). The hazard posed by the PME lamppost is what it already is and isn't made unacceptable by installing another bit of metalwork nearby (whether a fence or a cycle stand or a TT'd EVSE).


    Indeed I might question how "conductive" to touch all these items are in practice - steel lighting columns are usually heavily painted, likewise car bodywork, car door handles and charging connectors tend to be plastic, outdoor footwear usually insulating, posts for roadsigns plastic coated and so on. Nothing you'd want to rely on in lieu of basic insulation of course, but nevertheless they must reduce the chances of a shock in practice. What is the real probability of someone coming to harm even with a broken CNE?


        - Andy.
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