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What earthing arrangement is this?
Former Community Member
The supply is from a private transformer in a four core cable 3ph + n. The cable armour is earthed and connected to the MET. However there is also a green and yellow cable connected to the neutral terminal at the main isolator going back to a the transformer casing. The transformer is only 5 or 6 metres away. I think this must have been intended to make it a tncs supply but seems to me to just create parallel neutral conductors. Or is it tn-s-c-s? I have only been able to go off visual inspection because I could not disconnect the supply..
Apart some special circumstances you are not allowed to combine the neutral and earth in the consumers installation. The "S" in TN- C- S means separate. So we colour our protective conductors green/yellow even if they are connected to the supply neutral.
I am a bit sceptical about the arrangement in the OP. Having a neutral coloured green/yellow run outside a SWA armour with one inside is a bit worrying! Running a separate earth with SWA or AWA cables is common practice but they are connected to the earth bar not the neutral.
Apart some special circumstances you are not allowed to combine the neutral and earth in the consumers installation. The "S" in TN- C- S means separate. So we colour our protective conductors green/yellow even if they are connected to the supply neutral.
I am a bit sceptical about the arrangement in the OP. Having a neutral coloured green/yellow run outside a SWA armour with one inside is a bit worrying! Running a separate earth with SWA or AWA cables is common practice but they are connected to the earth bar not the neutral.
