mains earthing - yet again

[Toom Tabard]

After delay of 3 weeks, DNO have completed paperwork and I go into the queue to get my almost TN-S earthing (bonded to pipe) replaced by their official TN-S (bonded to cable sheathing) system.

Now the next corner I'm painted into - obviously the ideal time to connect the new earth cable to my rather old fuse box would be when everything is isolated before they activate the new fused cutout provided with the new earthing - that would be a two-minute job. But DNO say they leave me my old earthing connected, and provide a new coiled-up earth cable where it is up to me to arrange connection. And I find there is no isolation switch between the meter and consumer unit (nor apparently is there a regulatory requirement for one ) - and getting one would be a new and separate DNO application - there is only the fusebox switch to isolate anything beyond that. So there is the problem that an electrician, to operate safely, would apparrently have to get the DNO to come and take out the main fuse in the cutout to provide isolation!!!

Anyone know how this is usually handled? What I need is a simple earth cable connection job. Is it possible and compliant for an electrician to join/splice my cable from the box to their new cable - no doubt theirs will be required by the regulations to be thicker and weightier than mine. The good news is I've become somewhat expert on earthing - the bad news is I've moved into the realm where '1984' meets Franz Kafka in terms of regulation and everyone covering their backs by drawing demarcation lines.

All I need is compliant earthing now - my electrics seemed reliable, safe and operational until recent problem occurred- I'd shouldn't have to look at upgrade/re-wiring for a few years yet - I'd prefer lots of time to plan that stage.

Cheers

Toom

[Dave Osborne]

I don't quite understand your problem - possibly because it isn't a problem ;-)

Normally, you would have an earthing block like this:

with a label:

DNO earth wire would be connected to this block, as would your consumer unit and your main equipotential bonding.

Like this:

can be achieved safely by turning off the consumer unit at the main switch (even replacing the earth wire in the consumer unit for a larger one).

[Andrew Mawson]

apparrently

electrician

weightier

earthing -

Do what everyone else does - pull the company fuse - do the work and pop it back. Never yet been challenged on the lack of a seal on a company fuse. Wouldn't touch the meter seals though!!

AWEM

[Toom Tabard]

Many thanks, Dave

Haven't got anything external like that, but indirectly, you may just have solved it. At present my main earthing wire emerges from a hole beneath the fuse box and is bonded to the incoming supply pipe. My equipotential bonding, together with all the circuit cables, emerge from the ceiling above the fuse box and disappear into the box. So, assuming there is a corresponding earth connection bar for the bonding and circuits, it is inside the consumer unit and is part of it.

However, from what you say, could I fit such a block below my unit, connect my mains earthing from the consumer unit to it, and connect DNO earthing wire to it ?

The equipotential bonding aspects are about to be looked at separately as part of my central heating boiler installation, but would it matter if they are presently connected in the consumer unit and only one wire is emerging as a composite? As I say, there must be some bar(s) in the unit . Otherwise, what you are suggesting seems basically my idea of connecting/splicing the two cables.

So, is this just called an 'earthing block' that I can pick up anywhere?

I'd really be relieved if this is a non-problem.

Is it possible for an electrician to dig into the consumer unit to attach a higher capacity earth cable just by turning off the main switch incorporated in the unit? I thought there was a problem with the main/live output from the meter being directly connected if there was no DNO isolation switch.

I'm really encouraged by the info you've given. I hope it points to an easy solution. Wish the DNO was as helpful.

Regards,

Toom

[Toom Tabard]

That had occurred to me as one answer, but I didn't know has feasible it was, or how prevalent.

Thanks,

Toom

[Dave Osborne]

At present my main earthing wire emerges from a hole

There is indeed an earth bar in the consumer unit and if your main equipotential bonding conductors are connected to this earthing bar, then (provided the earth wire from the consumer unit to the new earth block is 16mm2), you can leave the main equipotential bonding conductors where they are.

Yes, of course. This is what is shown in the picture.

If you replace the main equipotential bonding conductors, then you could either connect the new cables to the earth bar in the consumer unit or to the new earth block. I would connect them to the new earth block as a matter of course, but it's your choice. You need to make sure the earth wire from the consumer unit to the earth block is 16mm2.

Yes, including eBay, B&Q and probably other sheds. You are obliged by the regs to have a label associated with the earth block. You likely will not get the label from a shed, but you can use the label from a Tenby earth clamp if you wish. The label only has to be permanently affixed with the prescribed wording; it doesn't have to be black on yellow.

I'd really be relieved if this is a non-problem.

Yes, that's what I said above. The incoming meter tails in the consumer unit are (or should be) insulated, so you can work inside your consumer unit with the consumer unit main switch in the off position.

I thought there was a problem with

See above.

It is very straightforward. nothing to worry about.

[John Rumm]

It depends a bit on the CU in question. If its a wylex style box with rewireable fuses, then its safest to work on when isolated - there is a certain amount of live metalwork inside that could be contactable if fiddling about. A modern CU however, could have a new earthing connection made relatively safely even with the power still on - the only live bit will be the (shrouded) terminals at the top of the main switch where the tails come in. So unless you go poking things into the terminals from above its actually quite hard to find something live when the main switch is off.

Its possible to join (although not desirable). However taking the new earth directly to the main earthing terminal is by far the best way. Note the MET is not always in the main CU - it can be a separate block.

The official line is that one would arrange for a temporary disconnection for the work to be carried out. The reality is that 99.9% of electricians will simply pull the main fuse, and get on with it. If you are getting a nice new main fuse into the bargain, then there is very little practical risk in pulling it.

[David Hansen]

On Mon, 13 Sep 2010 04:51:17 -0700 (PDT) someone who may be Toom Tabard wrote this:-

I imagine that your rather old fuse box has shields over the incoming cables. With a lot of the old ones these are slid in place when the main switch is opened, as they are attached to the switch. If that is the case then the electrician can open the main switch and, provided they take appropriate precautions, connect up the new earth cable.

If such shields are not fitted then no work can be undertaken on the fuse box without studying the situation, including fitting the earth cable. There may be a reasonably practical way of doing the work, but if there is not the only solution is to insert an extra main switch in the meter tails. It depends on the fuse box.

[Toom Tabard]

Dave, Many thanks for all that info - I'll follow it up

Regards

Toom

[David Hansen]

On Mon, 13 Sep 2010 06:18:59 -0700 (PDT) someone who may be Toom Tabard wrote this:-

In the days of old if the meter reader spotted this it would be sealed again. However, that was in the "bad old days", these days they probably wouldn't even notice.

However, three cautions. 1) turn the main switch off first. 2) remember that one of the terminals behind the fuse carrier is still energised and is protected by a fuse rated at several hundred amps, so a lot of current will flow if you short it, enough current to melt thick copper wires. 3) the main switch may not isolate everything, unlikely in a house but in an office building I am familiar with someone wired the emergency lights up to the incoming side of the main switch, so be prepared for sparks on removing and inserting the fuse.

[js.b1]

To OP... Do not pull the fuse if the meter is still turning with everything OFF. Do not insert the fuse unless everything is OFF, so you do not insert the fuse on a fault.

Fuse carriers of the BS1361 BS88 type often have a plastic guard over the live terminal, but it is pretty useless if you are wrestling a bit of 16mm 6491X or 25mm 6181Y tails into place and thus easy to get the end to just poke in by sods law. So it would be very wise to remove the fuse from the carrier and refit the carrier in place whilst working.

To be honest, book an isolator fitment.

Fit the MEB yourself and MET - the simple ones referenced at TLC are quite fine, there are very fancy ones with bridging bar and such like but they are expensive.

[chris French]

In message , Dave Osborne writes

spare earthing clamps at the time, so I printed myself one up. goggled around for a suitable image, wasn't hard to find one from a label seller.

Printed it out onto glossy photo paper and stuck it up.

[Toom Tabard]

Many thanks again to Dave and to all others who gave info. I suppose maybe it says something about my planning that when, twenty-eight years ago, I had the luxury of getting possession of the empty house three weeks before moving in and could let builders, electricians and joiners let rip, that our provision of power and light sockets was so generous that it is still adequate (apart of course from the extension boards near for our home computer stuff!! - In these days, I'd just taken delivery of a room-sized VAX11 at work) and no-one has touched the consumer unit in all these years. I've managed to find a electrician who seems very knowlegeable on the local issue of earthing problems caused by utility companies. He's coming to have a look to ensure there are no hidden issues I haven't been aware of. Here's hoping I just need the DNO to supply the earth, and it's a few minutes to swap for existing earth cable. Then the one day boiler installation job abandoned three weeks ago might finally get its day.

Regards

Toom