Is there a minimum size for the cover on an earth rod?

[ericmark]

Due to having an UPS, I have an earth rod for the inverter should the DNO supply fail, this is connected to the rest of the earths, and where I intend to pave in due time, the cover is a conduit box, with a sticker on it. This seems rather small to protect against shock should I have a loss of PEN.

If I cover with slabs this should then be OK, but can't remember any regulations as to size of cover on an earth rod, is there any?

 

[SUNRAY]

That seems to be a standard pre labelled item these days.

 

[Murdochcat]

Are you suggesting that you pave over the cover?

 

[ericmark]

I want to extend the patio, and will be driving the earth rod further into the ground and covering next year some time, the patio is too high, over the damp coarse, it was a double garage but now a flat, and we hope in the future to fit a lift between main house and flat, so it can be used more.

The earth rod is because we have batteries, inverter, and solar panels which can supply freezers, and central heating should we loose the DNO supply, so that the neutral in a power cut is referenced to earth, the inverter auto connects neutral and earth when the DNO supply is lost.

However when the DNO supply is connected, it is connecting the DNO PEN to earth, and if there should be a broken PEN, then even with my isolator switched off, so no DNO supply into the house, there could be a fair current going through the earth electrode, and there will be a gradient of voltage as we move away from the earth rod.

In all my time in the UK only had first hand experience of a loss of PEN once, it was a radio hams home, and he had an earth mat for his transmitter bonded with 4 mm² to the TN-C-S earth of the house, he realised some thing was wrong, turned off his main isolator, but his earth cable became a line of copper globules where it had melted.

My earth rod is no where good enough to cause that sort of current to run, and loss of PEN is rare, but using a word search for earth electrode in BS7671:2008 found loads, but nothing about size of cover over an earth rod. I expected some thing like this

but got like this

but only a single depth of conduit box.

The installer showed me the loop impedance on his meter, less than 1Ω, clearly an error some where, a single earth rod would never be that low, but not got around yet to measuring myself, I suspect he removed the wrong wire from the earth block to test. He also removed the boiler from any RCD protection, which also seems wrong, I know it is a FCU not plug and socket, but would have expected it to be RCD protected, it was before they fitted the solar, it was fed from an RCBO.

 

[JohnW2]

... where I intend to pave in due time, the cover is a conduit box, with a sticker on it. This seems rather small to protect against shock should I have a loss of PEN. /// If I cover with slabs this should then be OK, but can't remember any regulations as to size of cover on an earth rod, is there any?

I'm unaware of any regulations which require an earth rod to have a 'cover',let alone specifying a minimum size for such an item.

Do you really believe that there is a significant risk that someone would be touching an earth rod at the very same time that there was a ('vwery rare') 'loss of PEN'?

As has been asked, are you really saying that you intend to pave over the earth rod? If you did that, it would surekly not be accessible for inspection?

 

[ericmark]

Slabs lift easy. I see your point, thanks put my mine at ease.

 

[JohnW2]

Slabs lift easy.

Fairly easily (unless they are cemented down ) - but would the average electrician actually bother to lift them?

 

[333rocky333]

may be worth looking in regs under labels and identification, some labels have to be certain format, if there is one relevant , then that would denote the minimum size cover

 

[JohnW2]

may be worth looking in regs under labels and identification, some labels have to be certain format, if there is one relevant , then that would denote the minimum size cover

I thought of that, and looked, but the requirement for marking/'labelling' required on an earth conductor is the same as for connection of a bonding conductor to an extraneous-c-p, or the MET (which often seems to be absent!) - and those little things used for bonding & (sometimes!) METs effectively do not impose any minimum size on what they are attached to.

In any event, as I said, since the regs don't impose any requirement at all for a 'cover' to an earth electrode, I can't see how they could impose any minimum size for that cover (which did not have to be there ).

 

[ebee]

As far as I am aware an earth rod should be accessible for inspection and testing and given some mechanical protection from inadvertent damage so a bit that you can get to in order to disconnect and test should be the joint (say clamp to lug where the earthing conductor joins to the rod and the joint itself given a little protection from the elements.
Seems to me that the box itself merely gives a little indication of where that joint is as a info/warning and to some extent gives a little protection from rain etc corroding that joint, you might smear a little Vaseline etc around it once assembled, I would not hide that connection under concrete or flags etc unless it is connected to the conductor via a robust sufficient method. Then your tests could be alternatively made from the other end of the earthing conductor but you can not visually inspect the rod end connection so I would prefer to avoid that.

If a rod is internal to the property and under a floorboard for instance then it would not usually need a cover anyway, just some clue as to where it might be.