O PEN Devices and Supplies

but give it a few years of hacks and changes and it won't be, and there may be scope for a few nasty accidents when things like water meters are replaced .

I’ve got a very thorough plumber, his apprentice once asked him why he uses a set of crock clips to bridge the gap before removing a section of the water pipes. Obviously the lad was confused as to how this helps prevent electric shock if there’s an earth fault. “Go and ask the sparks” I drew him a little picture with a very unhappy plumber holding onto one piece of pipe with one hand and the other piece with the other during fault conditions! I hope he remembers that in years to come when he’s feeling lazy about going to the van for his temporary equipotential bonding clamps.

perhaps he should carry a clamp meter. Still, a jump lead is a good idea working on an installation of unknown condition - which it probably most. I suspect though such caution is the exception, rather than the rule.

Mind you fast forwarding to about 60 seconds into this video after the long talking intro about chat rooms for gas engineers , that image should hammer the point home to anyone who doubts.  Would you wish to undo that main bond without gloves ?

(a clearer demonstration of PME arcing problems I have not seen . An AFDD or indeed switching off at the main will probably not help a fat lot here either.)

Mike.

I foresee the same with OPDDs, starting with the next edition of the EV code of practice I suspect they will become the preferred option where an installation is PME and eventually I suspect all new TN installations will require one. 

There was a suggestion a while ago that open-PEN detection (based on L-N voltage) could be easily built-into smart meters - they already have voltage measurement and a contactor already built-in - even if they only disconnected the load leaving the PE connected it would be an improvement (if all loads were removed then the PEN wouldn't be at a hazardous voltage) - and of course they can automatically inform the DNO of the problem and possibly wait for the DNO to signal that the repair had been made before reenergising).

But of course we live in a world where we couldn't even get the smart meter installation program to include an isolator, so that's going to be far too much like joined-up thinking....

    - Andy.

The suggestion re SMART meters would not be to disconnect the installation (that may also not take away the problem due to diverted neutral currents and shared extraneous-conductive-parts) but instead to notify the DNO so they can investigate.

I believe this is proposed for (if not actually being implemented right now in) Australia.

IronFreely said:

I’ve been thinking about this a lot recently and I’ve been asking myself why it’s taken EVs to bring in OPDDs…. In the UK there are 400 Open PEN faults recorded by the DNOs annually, 1% of these result in electric shock, 25% of which are serious resulting in hospital treatment or death (death is actually quite rare).

Detecting the fault is one thing ... what do you want to do when you've detected it?

Disconnecting L and N, even at the meter, doesn't take the problem away. The only real way (because of actual or fortuitous "bonding" downstream of the protective device) is to fit the disconnector preferably immediately before the piece of current-using equipment that the person may be touching.

Makes the "disconnecting device" approach OK for a single EV (as the EV itself is insulated by tyres from the ground, and hopefully other metal) but not for installations, or groups of circuits, and indeed certain circuits with fixed installed equipment (like boilers) on them.

a clearer demonstration of PME arcing problems I have not seen

Impressive! I wonder what's triggering the arc? I'm guessing there's a consistent small gap between conductive parts somewhere - most unusual for plumbing fittings (either metal-to-metal or metal-to-plastic).

   - Andy.

Well given the hissing and spitting, the dreaded high resistance char I expect. It is quite likely to be some sort of organic jointing compound, perhaps a grease or a putty-like thing between two metal parts, that conducts to a degree, and is heated and pyrolysed to produce something more like a sooty carbon deposit that has a resistance  of several ohms that then heats up and does more burning/ boiling off of any oil or moisture.

I think it might be a compression type copper to lead transition, and if it is, then something like "plumbers mait" may have been used, but I am only guessing.

A properly sweated lead to copper soldered joint would probably have been good for half a kA at least with water running in the pipe, but no-one does those any more.

Mike.