Is this a TNCS PNB? Large Commercial Site with local 11KV Tx

Paultrim123321 · May 14, 2012

Hi All

Sorry for the poor photo's, just after some clarification as to the arrangements at source of the supply below. No info from the DNO with little info available in the sub. Photo 2 clearly show a PEN between the neutral and the earthing bar in the section board. I am presuming this to be PNB but would appreciate some advice please gents. For info, the Tx is 11KV with local metering on the LV side adjacent to the LV Section board.

johnboy6083 · May 14, 2012

The neutral is linked to earth at either the tx, or in the main panel. Most I've seen are linked in the supply side, in the cable chamber below the ACB.
Although these systems are sometimes called TNC-S, I don't believe that they share any of the characteristics, and I'll stick my neck out here, and u would design bonding as TNS

Paultrim123321 · May 14, 2012

The photo was taken at the main panel which is located approx 2M from the Transformer.

Knobhead · May 14, 2012

It’s TN-S standard set up for a MV/LV transformer.
The removable link is purely for “dead” testing. As John said the normal location is on the incoming on the switchgear before the main ACB. Very rarely will the earth link be fitted in the transformer.

Engineer54 · May 14, 2012

Agree with Tony, this a typical TN-S arrangement made at the LV Main Switchboard. If this is a DNO transformer, for area distribution, then the chances are these days, that the neutral will continue to be grounded at every cable joint along the various cable distribution routes.

By the way, that MV cable termination into the Transformer isn't a good one. I'd almost certainly fail it, if presented to me on my project!! lol!!

Knobhead · May 15, 2012

I’ve just had a close look at the connections in PhotoShop.

There’s no soldered thimbles on the cores. Those clamps will never hold up under load.
The clamps alone can be used for SolidAl conductors but copper needs a thimble sweated on to stop the conductor being squashed and keep a constant contact area.

I’d condemn it out of hand!