Metal C.U (exsposed conductive part)

[ianphilip007]

hi all

quick question , have an outbuilding which has no extrenuous conductive parts (water,gas,steel frame construction) the supply is TN-C-S and the earth has been extended to the outbuilding. The existing C.U. is plastic but has become damaged, are there any problems re earthing/bonding if a more robust Metal C.U. were to be fitted. i cant think of any or will the the new metal C.U. be classed as an exsposed conductive part and require bonding back to the M.E.T (10mm2) 0r am i confusing this with extrenous conductive parts

many thanks

 

[Des 56]

http://www.electriciansforums.net/e...159-good-guide-exported-pme-outbuildings.html
There you go

 

[Deleted member 9648]

You are confusing the two terms....an exposed conductive part is part of the electrical installation and requires earthing.
An extraneous conductive part is not part of the electrical system but may introduce a potential,usually earth,and may require bonding.
The metal case of a CU will thus be the former and require earthing

 

[diditrain]

The metal C/U will be classed as an exposed conductive part and not an extraneous conductive part. No problem with it being metal construction

 

[ianphilip007]

thought so getting my terms mixed up, brain slowing, the metal c.u is earthed via the tncs earth, and of course it is an exsposed conductive part so no bonding required, and as stated there are no extrenuous conductive parts.

just to check. Metal / plastic C.U makes no difference when exporting tncs earth?

when working on TT supply (rcd protection on tails) if metal C.U. is used?

as you here so many myths re taking tncs earth to outbuildings,

 

[Deleted member 9648]

thought so getting my terms mixed up, brain slowing, the metal c.u is earthed via the tncs earth, and of course it is an exsposed conductive part so no bonding required, and as stated there are no extrenuous conductive parts.

just to check. Metal / plastic C.U makes no difference when exporting tncs earth? None whatsoever

when working on TT supply (rcd protection on tails) if metal C.U. is used? Or take precautions to ensure tails cant short out onto case...ie- bushing entry, DI tails,clamping to ensure no movement......100-300ma T/D RCD prefererred option.

as you here so many myths re taking tncs earth to outbuildings,.....Yep.....:banghead:

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