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EV TN system

lyledunn
722.312.2.1 in IS10101:2020 has only one stipulation and ignores all the TN-C-S issues highlighted in BS7671 2018 A1 regarding PME even though the vast majority of installations in Ireland are PME.

It says; "In TN system, the final circuit supplying a connecting point shall be a TN-S system". A rather unusual way of putting things. It sounds almost like a bit of bad translation. More to the point, I always thought that unless you had an intervening transformer TN-S referred to the whole system from source to final connected equipment.
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    If  describing the end to end system is always required/intended, then I would agree, but I'm not sure it always is, at least in the eyes of the standards writers.  I suspect they assume you can also use the same notation to describe a meaningful subsystem, such as just the  distribution, or just the consumer wiring, separately.

    This interpretation works, and allows the addition of more information, if the whole system has more than  the two CPC arrangements. If not there is the potential to run aground if you wish to describe anything more complex, for example let us consider the earthing of a TT island derived from distribution with a grounded neutral .


    That would need to be  written as  TNC-TT or TNC-S-TT or something for the whole end to end system, (first with no section using a neutral derived CPC, e.g. whole house TT,  and the second if we were talking about an island for an outbuilding perhaps on a TNCs main building) but normally I'd refer to it simply as "a TT installation" - but of course this only refers to the subsystem downstream of the CPC break.

    I must admit the longer form would be more descriptive, and perhaps quite helpful, but I'm pretty sure that I've never seen it.

    M.
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    If  describing the end to end system is always required/intended, then I would agree, but I'm not sure it always is, at least in the eyes of the standards writers.  I suspect they assume you can also use the same notation to describe a meaningful subsystem, such as just the  distribution, or just the consumer wiring, separately.

    This interpretation works, and allows the addition of more information, if the whole system has more than  the two CPC arrangements. If not there is the potential to run aground if you wish to describe anything more complex, for example let us consider the earthing of a TT island derived from distribution with a grounded neutral .


    That would need to be  written as  TNC-TT or TNC-S-TT or something for the whole end to end system, (first with no section using a neutral derived CPC, e.g. whole house TT,  and the second if we were talking about an island for an outbuilding perhaps on a TNCs main building) but normally I'd refer to it simply as "a TT installation" - but of course this only refers to the subsystem downstream of the CPC break.

    I must admit the longer form would be more descriptive, and perhaps quite helpful, but I'm pretty sure that I've never seen it.

    M.
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