You cannot post a reply to this discussion. If you have a question start a new discussion
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..
. . . If the neutral point is the point where the three phases' neutral-ends meet (in or on the transformer), then the conductor in question in PNB is a PEN by this definition. Here, again, this would not have been my choice when thinking about the effects of a break in this conductor with no other fault in the system. Even a TT system could by this definition have a 'PEN conductor' if the neutral from the source runs as a wire to the first earth electrode and then on to the customers, as is often found in overhead supplies with separate HV/LV earthing where the LV earth is at the "next pole". . .
No. A PEN conductor combines the earth and neutral functions - it carries load current under normal circumstances. Your fist example is TT, your second example is likely to be TT, but would be TNC-S if the DNO offered their neutral conductor in place of an earth conductor. You would need at least two earths, one at or near the transformer before the first service branch on that distributing main, the other on the main, at or after the last service branch.
. . . If the neutral point is the point where the three phases' neutral-ends meet (in or on the transformer), then the conductor in question in PNB is a PEN by this definition. Here, again, this would not have been my choice when thinking about the effects of a break in this conductor with no other fault in the system. Even a TT system could by this definition have a 'PEN conductor' if the neutral from the source runs as a wire to the first earth electrode and then on to the customers, as is often found in overhead supplies with separate HV/LV earthing where the LV earth is at the "next pole". . .
No. A PEN conductor combines the earth and neutral functions - it carries load current under normal circumstances. Your fist example is TT, your second example is likely to be TT, but would be TNC-S if the DNO offered their neutral conductor in place of an earth conductor. You would need at least two earths, one at or near the transformer before the first service branch on that distributing main, the other on the main, at or after the last service branch.
