TPN SOCKETS OUTDOORS

Not a job I would agree to test and inspect, it’s out of my league.


Is it a quarry or a materials handling site? I would assume that if it is a quarry then the additional requirements for quarries and mines apply to it rather than just  BS7671 and the machinery requirements if it is just a transfer facility.


 Andy Betteridge.

If it was new you could install 30 mA RCD protection and probably be half way down the street before there was a trip.


Andy Betteridge.

If it is correctly designed, then it should be no worse than any other motor driven kit  intended to live outdoors- and to be honest if it leaks 30mA to earth more from one phase than the others then it has probably got wetter inside than it should. There are mining  installations with what are in effect 3kV extension leads with connectors running in mud without issues. Enclosures and louvred  vents can be organised to keep things cool and still be dry in the mud and rain, though I agree there are plenty of examples in practice, especially agricultural practice, that are not as good as they could be, and a higher leakage threshold may be a work around  for the first start after a long idle period until the things warm up a bit.

The bigger source of grief in terms of earth leakage will be if there is a VFD in the box,  and that is probably also the biggest risk for premature failure if the PCB with the electronics suffers from the green copper plague.

You have not mentioned the human factor, whilst abusing the equipment may not be deliberate it may be a result of working in a harsh environment.


Andy Betteridge

Since it would be classed as 'Portable Equipment Used Outdoors' then depending upon motor rating, all of the conveyors we inspect/test/connect up have to have 30ma rcd protection. Generally, this is via a plug/socket arrangement with an integral 4 pole RCD , with the socket being fed from a main control panel and it's wiring protected accordingly for the rating.

Yes, probably.


I assume that the sockets are 32 A.

411.3.3 an exception may be provided for (i) if a documented risk assessment determines that it is not necessary. (You would need to see the actual document.) The furthest left socket may have individual RCD protection. If it is intended that the other sockets are used for a fixed purpose, perhaps being provided with a view to isolation for maintenance (Table 537.4), (ii) need not apply - the equipment does not appear to be "mobile".

I would assume that if it is a quarry then the additional requirements for quarries and mines apply to it rather than just  BS7671

Is that still the case? As I recall the 'mines and quarries' exemption to BS 7671 changes to just 'mines' a release or two ago.

   - Andy.

From the photo it looks like the topside of a coal mine to me.

I see a conveyor, which looks to be on a plug and socket arrangement - surely a 400v trailing lead mandates rcd protection in any case?

I hate to see steel, even coated steel enclosures used outside like this. The ones we find on site are generally ill-installed,and  bashed to bits, thus no maintenance of IP integrity and much ingress of all kinds of rubbish.

This is a dockside coal yard that sorts and grades thousands of tons for onward delivery to wholesale customers and the company’s own bagging plant. The sockets are just convenient means for connecting the conveyor motors. There is a TPN socket just outside the picture which is fitted with a 30mA RCD. This was specifically for power washing and has a notice to that effect but it got hit by a lump of coal and, although not dangerous, no longer functions. They do the power washing when the plant is idle but whilst the guy doing it has no idea of the merits of a 30mA RCD, he is cute enough to start the conveyor and use one of the motor ports. 

It’s hard to risk assess initiative!