Use of ECBs

[Radio Fixer]

Ah! good on you Lawrence.

I have now understood something else on that consumer panel of mine. In the picture the unit serving the outside lights etc is an RCBO.

   

So I have 5 circuits on one RCD and 6 on another and then an RCBO for any outside wiring that some nasty with a pair of insulated cutters can snip without affecting the other circuits.

Gary

[pwdrive]

" The Neutral should be bonded to Earth at the Meter and be tagged as PME. "

Well now another two things I don't understand. What does PME stand for? And the neutral being bonded to earth. To me that is a No! No!. The neutral has volts on it and I have always understood that it should not be connected to earth at the domestic premises. I was told it is connected to earth back at sub station or the transformer that splits out the phases.

Well I hope it was the mower and yes you don't actually need an earth to it. The RCD trips because on an unbalance in the L and N wires. I will have to try it again sometime. But it still seems unlikely the lead is in good order and when I cut the stalks off the grass it was bone dry. We hadn't had rain for about a month. Gladly we had some last night.

Gary

PME means as in post #10 as far as I know.

There are various earthing systems, I'm not an expert but here our house wiring earth from the consumer unit is connected to the DNO's neutral at the meter box using a 10 mm earth cable, legally only the DNO can connect that. From there the neutral and the live goes to the top of a utility pole in the garden, I was told there was also another connection from the neutral at that point down to a buried ground mat or spike.

Once the DNO's neutral and PME reach the consumer unit they go there separate ways and must not be connected together under any circumstances even though they are connected together at the meter box.

Lawrence. EDIT: I've referred to this in the past, the system at our place is TN-C-S :

electrical.theiet.org/wiring-matters/16/earthing-questions.cfm?type=pdf (copy and paste into your address bar)

[AlanBeckett]

In days of old, when Knights were bold, etc, etc, a typical UK Domestic Installation consisted of a Substation feeding a Street or Streets with 3 Phase. Each house got a Phase and Neutral and provided its own Earth, typically the incoming Lead Water Pipe or other suitable arrangement. Thus every third House was on the same Phase. The snag is that any unbalance Current flows back down the Neutral, and there would be Voltage on it. At out last house you could often find 30 Volts on the Neutral, and bear in mind that it's backed up by the Sub. If you lost the Neutral somewhere, typically due to corrosion or damage, the whole of the 'Dowside' would rise to Phase Voltage. It was generally OK when the consumption by each House was low, but as lots of high Loads were added the problem got worse. The solution was to bond the Neutral to the incoming Earth, provided with the Supply, at each Meter point, hence 'Multiple Earthing'. Now any unbalance Currents flow to Earth at each House. I believe it was also driven by the use of Plastic Water Pipes where you could no longer rely on the incoming Pipe to provide you with a decent Earth. Note that Bonding the household Metallic Pipes to Earth is NOT to Earth the Supply, it's to Earth the Pipes - Eqipotential Bonding - so you won't get a shock between Neutral and a Pipe.

There's a proper explanation on the Net.
Come on Lawrence, you're good at finding these things.

Alan

[pwdrive]

Here's something for starters:

http://www.tlc-direct.co.uk/Book/5.6.3.htm

Lawrence.

[pwdrive]

And a working link from the duff link attempt in my post #22

Lawrence.

[pwdrive]

Which begs a question from me, our caravan, it's a timber one not metal, an armoured cable from the house to the caravan has been laid, it's three core plus the galvanized multi strand protective sheathing, neither end of the cable has been connected up yet, the caravan has a mini ring main installed and a lighting circuit and an electric shower all going to a small consumer unit within the caravan, do I rely solely on an exported PME connection from the house once the cable is connected or do I sink an earth spike at the caravan end as well or is there another arrangement? I did ask our electricity supplier, they said go speak to an electrician, I spoke to an electrician and he said it's £30 an hour when do you want me to come round..

Lawrence.

[Radio Fixer]

Protected Multiple Earthing. Don't think I have it and don't think I'm bothered whether I do or not in so far as I don't think it affects my installation and what I'm trying to achieve.

But I hate not understanding and I will digest your wisdom Alan and follow up on Lawrence's lead and get back if I'm still a dummy !!

thanks Gary

[pwdrive]

Gary, here's a couple of pictures I just took of our recently installed meter box etc, the first shows the bottom of the DNO's junction box with the incomer, the other pic is the top, the neutral and the house wiring earth return are connected together inside it, 'scuse the dead wildlife...


Lawrence.

[AlanBeckett]

Ah, the wonders of Standardisation. Meter Tails used to be Red and Black and you didn't need to label them.
Progress?

Alan

[pwdrive]

You can just see the bottom of the new electronic meter, that wasn't there when I fitted the meter box, originally the old meter and cable was inside the house, when they came to connect up the new tails and earth they used the old meter again, meanwhile EDF had been sending me letters for four years saying that the old meter must be replaced as a legal duty, as usual the letters ended up in our tear up and laugh department, eventually they got kinda tough so I succumbed, we always have the meter man/person to read the meter but today I got a letter saying can I phone their new automated line with the reading "Was that a nine "...No it was a five.."Was that a nine"... I think I will lose the meter box key, stick some underpants on my head and two pencils up my nostrils and wait 'till they come round to investigate.

Lawrence.