please help

tizbad · Jun 20, 2009

hi, i went to a neighbours farm to help replace a broken motor, no problem. its supllied from a 3 phase board. however, the board is supllied via a 4 core armour with the armour providing the earth. i spoke to a colleague who says this is wrong. he says the submain should be rcd protected (300mA time delayed) banjoyed at the supply end, but not at the 2nd. board as this should have a tt stake fitted providing the earth. also the armour at the 2nd board should be insulated from the 2nd board so as to not export pme. is this correct
thanks

MySpark · Jun 20, 2009

you check with the supplier, some will not let you earth remote buildings to their MET,s, so yes you may have to TT it however any metalic cable covering must be earthed earthing it to the TT system is the correct way at both ends if possible. any TT system must have a minimum 300ma rcd for fire protection.

lewlec · Jun 20, 2009

hi

pme is not permitted in an agriculture installation, there fore the earthing arrangement needs to be tt.
so yes you could isolate pme at 3phase board and have 300ma rcd as main incomer then have 30ma rcbos for socket outlets, or make whole installation tt and have 300ma at origin.

hope this helps