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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..
there is a certain amount of copying in class going on
I agree - I have been told by folk who should know better that there is no such thing as TNS PNB , if it is PNB it must always be TNCS.
To which I say, unless there is a PEN, and two points where N and E link it cannot be. The point about earth fault detection is a good one, and chimes in as the big current version of the error folk make with an RCD on a small genset with floating windings.
By all means insist, as many DNOs do, that it should be bonded as if TNCs, as one day there may be another building added on the same transformer with a CNE supply, but that is not the same at all as the private case when it is all under one control.
But then the same technical authorities are unable to separate heating due to magnetic hysteresis and that from eddy currents, and have a very wrong, but well copied diagram showing current in loops in the metal around a wire penetration.
there is a certain amount of copying in class going on
I agree - I have been told by folk who should know better that there is no such thing as TNS PNB , if it is PNB it must always be TNCS.
To which I say, unless there is a PEN, and two points where N and E link it cannot be. The point about earth fault detection is a good one, and chimes in as the big current version of the error folk make with an RCD on a small genset with floating windings.
By all means insist, as many DNOs do, that it should be bonded as if TNCs, as one day there may be another building added on the same transformer with a CNE supply, but that is not the same at all as the private case when it is all under one control.
But then the same technical authorities are unable to separate heating due to magnetic hysteresis and that from eddy currents, and have a very wrong, but well copied diagram showing current in loops in the metal around a wire penetration.
