TNCS 6mm main earth - EICR

Thanks for that Andy.


I have a copy of the 14th Edition of the "Regulations for the Electrical Equipment of Buildings" 1966 published by the Institution of Electrical Engineers, now the I.E.T. My edition contains amendments up to 1976.


Table D.2M shows the sizes of earthing leads etc. required, related to the nominal cross-sectional area of the associated copper circuit conductor. The earthing lead is now called the main protective conductor.


If the main tails are 10.0mm2 or 16.0mm2 then the earthing lead is required to be 6.0mm2.


Earth continuity conductors, (circuit protective conductors) should be 6.00mm2 minimum.


Bonding leads should be 2.5mm2 minimum.


Of course the 850 Amp high fault current will only occur at the main terminals, down stream with higher Zs values the fault currents will be lower, but then final circuit protective devices like M.C.B.s will disconnect those lower earth fault currents.


Out of interest, back then, a maximum  earth fault loop impedance of 1.35 Ohms was allowed for a circuit protected by a 60 Amp semi-enclosed or cartridge fuse having a fusing factor exceeding 1.5,or 0.8 Ohms for a 100 Amp fused circuit. (Table D.1).


Z.

Thanks for that Andy.


I have a copy of the 14th Edition of the "Regulations for the Electrical Equipment of Buildings" 1966 published by the Institution of Electrical Engineers, now the I.E.T. My edition contains amendments up to 1976.


Table D.2M shows the sizes of earthing leads etc. required, related to the nominal cross-sectional area of the associated copper circuit conductor. The earthing lead is now called the main protective conductor.


If the main tails are 10.0mm2 or 16.0mm2 then the earthing lead is required to be 6.0mm2.


Earth continuity conductors, (circuit protective conductors) should be 6.00mm2 minimum.


Bonding leads should be 2.5mm2 minimum.


Of course the 850 Amp high fault current will only occur at the main terminals, down stream with higher Zs values the fault currents will be lower, but then final circuit protective devices like M.C.B.s will disconnect those lower earth fault currents.


Out of interest, back then, a maximum  earth fault loop impedance of 1.35 Ohms was allowed for a circuit protected by a 60 Amp semi-enclosed or cartridge fuse having a fusing factor exceeding 1.5,or 0.8 Ohms for a 100 Amp fused circuit. (Table D.1).


Z.