What level of voltage is dangerous Zoom? or can we turn it round and say what voltage is safe? Answer -Zero Volts. Equalise yer voltages as far as possible and you are relatively safe in that respect. I suppose those added words do not really change the intention but merely enhances the meaning of things to the unwary

The expression needs expanding as on its own it is meaningless. How can an extraneous-conductive- part introduce a dangerous potential difference into an installation? It is normally at Earth potential.

Z.

To my mind the extra words are strictly speaking unnecessary - as the concept creating a hazardous potential difference by introducing a another potential into the installation is already covered in the definition of an extraneous-conductive-part. I guess they've just put them in there to reinforce the "change" (i.e. a change of attitude, not of underlying principles) that internal metal pipework only connected to the outside by plastic pipework, need not be bonded.

  - Andy.

How can an extraneous-conductive- part introduce a dangerous potential difference into an installation? It is normally at Earth potential.

The key concept there is potential difference, rather than absolute potential. If all the other metalwork inside your installation is at say 115V or 230V (even briefly due to an earth fault during clearance times, or for a longer duration, say due to a broken PEN conductor), then a part held at true earth potential creates a hazardous potential difference, across which someone could receive a fatal shock.

   - Andy.

What about a lost neutral? If everything else is getting on for 230 V, the kitchen tap at 0 V introduces a dangerous potential difference unless it is bonded.

So it is not just the extraneous-conductive-part that is hazardous on its own. On its own it may be quite harmless. It is only hazardous in combination with other aspects within an installation. The wording should make this situation clearer.

Z.

Or the extraneous-conductive-part may export your 230/240 Volts to the outside. DANGER.

Z.

There could well be an extraneous-conductive-part that is NOT liable to introduce danger.

For example, if a metal pipe is converted to plastic within a very short distance - say 5 cm - of entering the building volume from the ground, contact with the short metal part is highly unlikely - the risk is further reduced if the floors are wooden, the metal is hidden away somewhere, and there is no risk of simultaneously touching it and any other conductive parts connected to the MET. So, in addition to being very difficult to effect a suitable bonding connection, bonding it would serve no purpose.

Note that in the same Regulation, the "insulating section" wording is now gone.