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Distribution circuit tt system

Discuss Distribution circuit tt system in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

havo one

havo one

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on a TT system today I had meter tails backed up by domestic 100A 88-3 fuse directly into fusebord, no main switch or RCD on tails which is very common in N.I, am I right to consider this as a distribution circuit?
my thoughts are that the fuse doesn't provide proper disconnection time and would need RCD. reg 411.5.4
Zs x Ia equal or less than Uo
my Zs is 74 ohms & from appendix 3 I see Ia =850A for 1s disconnecton

74 X 850 = 62900 ? any thoughts thanks
 

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