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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..
I'd respectfully suggest that anyone who thinks it is TT should be demoted straight back to only changing light bulbs.
A Private Neutral Bond like this can only be TN-something. The decision as to which depends if normal load neutral currents and earth fault current share part of the path to the electrode - which can only normally occur where there is more than 1 NE bond.
And by the way if you do have 2 NE bonds, it is only illegal on the consumption side, the "distribution" bit is fine having bits of TNC - normally by it reaches any sort of load with a neutral connection, we should be in the 'S' part of the TNC-S, and then having parted, never shall N and E meet again.
This one NE bond thing most commonly comes horribly unstuck where there are UPS, mains and Gensets to consider, and any one of them may be the sole source, especially with US sourced kit, as in their world, the distinction between N and E is a bit less clear.
I'd respectfully suggest that anyone who thinks it is TT should be demoted straight back to only changing light bulbs.
A Private Neutral Bond like this can only be TN-something. The decision as to which depends if normal load neutral currents and earth fault current share part of the path to the electrode - which can only normally occur where there is more than 1 NE bond.
And by the way if you do have 2 NE bonds, it is only illegal on the consumption side, the "distribution" bit is fine having bits of TNC - normally by it reaches any sort of load with a neutral connection, we should be in the 'S' part of the TNC-S, and then having parted, never shall N and E meet again.
This one NE bond thing most commonly comes horribly unstuck where there are UPS, mains and Gensets to consider, and any one of them may be the sole source, especially with US sourced kit, as in their world, the distinction between N and E is a bit less clear.
