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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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    mapj1:




    If the extraneous-conductive-part is bonded to one installation already, and you then bond it again to another installation, the second protective conductor [main protective bonding conductor] surely becomes common to both installations.




    But the idea that they are not bonded is something of a mistake, reliable isolation cannot be acheived, adjacent buildings share gas and water pipes accross multiple methods of earthing (TT and PME is commonly mixed on farms, where the house is PME, and the farm proper is very much TT. Both have water. Mixed TNC-s and TNs on the same substation is common in built up areas with mixed ages of property), not to mention water and gas pipes also interlinking the CPCs of multiple substations.


    perhaps we need to permit fuses and breakers in the CPC after all ?



     




    So, point accepted with respect of water pipes, but if everything is connected on PME, it will be OK.  TT for a building is a different story to TT for caravans, and EV charge points - they are another thing entirely.


    In terms of "Metal pipes serve TT and TN systems equally" - Well, that's how it WAS.


    If you TT a NEW installation, or charge point, DNOs have physical separation requirements from metal parts connected to their global earthing system, including a requirement to separate the earth electrode below ground ... but this is no problem, as we can put insulating sections on our incoming pipework now.


    This has just as much to do with the changes brought in when we moved from the old BS approach for combining HV and LV earthing - and the definitions of what's acceptable in terms of overvoltage impulses due to EPR from a fault in the HV network. We are now working to BS EN 50522 / BS EN 61936-1 values instead, and the current definition of what's "HOT" and not, and I guess the DNOs are being mindful of that. BS EN 50522 and BS EN 61936-1 replaced the BS's back in 2010.


    It's not plain sailing out there.

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  • 0

    mapj1:




    If the extraneous-conductive-part is bonded to one installation already, and you then bond it again to another installation, the second protective conductor [main protective bonding conductor] surely becomes common to both installations.




    But the idea that they are not bonded is something of a mistake, reliable isolation cannot be acheived, adjacent buildings share gas and water pipes accross multiple methods of earthing (TT and PME is commonly mixed on farms, where the house is PME, and the farm proper is very much TT. Both have water. Mixed TNC-s and TNs on the same substation is common in built up areas with mixed ages of property), not to mention water and gas pipes also interlinking the CPCs of multiple substations.


    perhaps we need to permit fuses and breakers in the CPC after all ?



     




    So, point accepted with respect of water pipes, but if everything is connected on PME, it will be OK.  TT for a building is a different story to TT for caravans, and EV charge points - they are another thing entirely.


    In terms of "Metal pipes serve TT and TN systems equally" - Well, that's how it WAS.


    If you TT a NEW installation, or charge point, DNOs have physical separation requirements from metal parts connected to their global earthing system, including a requirement to separate the earth electrode below ground ... but this is no problem, as we can put insulating sections on our incoming pipework now.


    This has just as much to do with the changes brought in when we moved from the old BS approach for combining HV and LV earthing - and the definitions of what's acceptable in terms of overvoltage impulses due to EPR from a fault in the HV network. We are now working to BS EN 50522 / BS EN 61936-1 values instead, and the current definition of what's "HOT" and not, and I guess the DNOs are being mindful of that. BS EN 50522 and BS EN 61936-1 replaced the BS's back in 2010.


    It's not plain sailing out there.

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