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Can you share earths?


Ford Anglia
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Just a question asked me by my wife, when I was last over there, struggling to bend 6 single core cables round a tight bend in a conduit.

They were LN&E for lighting and sockets. They later pass into a larger junction box, where the lighting goes one way, and the socket wiring the other.

Wife asked me why I didn't attach to lighting EARTH to the socket earth at the large junction box, and only have FIVE cables back to the distribution board? I had no real answer.

At the time, I was nearly there, so I continued doing it as I've described at the top of the post.

The recent post about "sharing lighting and socket wiring", brought the memory back.

IS it something that is a complete no-no? If so, why?

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No you can't. Each circuit has to have its own earth running along the same path as the phase and neutral for that circuit.

Also make sure you are using the correct diametre conduit. There are regulations for the number of wires and wire guages allowed down each conduit.

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[quote user="fulcrum"]No you can't. Each circuit has to have its own earth running along the same path as the phase and neutral for that circuit.

Also make sure you are using the correct diametre conduit. There are regulations for the number of wires and wire guages allowed down each conduit.
[/quote]

Yeah, the conduit wasn't the problem, it was the VERY unflexible French single cored cables! They would keep twisting around each other, and so increasing the amount of space needed.

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[quote user="fulcrum"]No you can't. Each circuit has to have its own earth running along the same path as the phase and neutral for that circuit.

Also make sure you are using the correct diametre conduit. There are regulations for the number of wires and wire guages allowed down each conduit.

[/quote]

Umm, thats not correct.  Your wife is very astute!  You can split the earth between the sockets and lights, so long as you  keep the 2.5mm2 running  back to the dist board and you do the joining in a box and not at the sockets.  Electrically, this is OK, however, mechanically its difficult to ensure a good connection when joining a 1.5mm2 to x2 2.5mm2, the choc/domino block always seems to leave the smaller wire loose, so I wouldn't recommend  it.  Your problem is probably due to too small a conduit.  I always keep the lighting and sockets cabling separate in individual conduits.  This keeps things simple and lets you drop the conduit for the lights and sockets directly to where they are needed and make fault finding in years to come easier.

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pcwhizz

I am sure when reading the French Normes that it states that all wires for a given cicuit should run along the same route from Tableau de repartition and that lighting and power sockets must be kept separate.You yourself have pointed out that it isn't easy to connect 1.5 to 2.5 wires in the dominoes and make a good connection. It also makes sense to have separate cabling for each circuit for easier fault finding.

If I'm not correct and it isn't in the French Normes, then I stand corrected.

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Fulcrum,

You still meet that rule as the earth wire will still run along the same route as the lines and neutrals, will it not?  Its just 1 wire and not 2.

Looking in my copy of the "L'electricite pas a pas" (sold at Bricolages)  in the conducteurs de protection section it clearly shows an earth wire being split 2.5 - running, 1.5 teeing off for lighting.  Interestingly it also shows the earth wire being shared by a washing machine, an oven and a light fitting.  The point is that the earth wire is distributed via jointing boxes and NOT via the sockets and light fittings.

As I said before, I always run the light wiring in its own conduit and jointing boxes, I find this much simpler,  and of course this means a separate earth wire is run for the lights.  You must always consider  the mechanical integrity of any electrical installation.  Its not easy deciding whats best, but keep it simple is a golden rule.  Sharing earths (even if it is allowed in the regs) can end up with an install looking like the inside of a pin ball machine!

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[quote user="pcwhizz"]Fulcrum,

Sharing earths (even if it is allowed in the regs) can end up with an install looking like the inside of a pin ball machine!

[/quote]

Agreed. That is why I keep it all separate. It makes testing installed circuit impedances much easier when the install has to be signed off..

Anyway I don't want to get in to an argument. Especially on this forum. Perhaps I should have said, in my original post, No You shouldn't instead of No you can't.

Peace  [:)]

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  • 2 weeks later...

[quote user="fulcrum"][quote user="pcwhizz"]Fulcrum,
Sharing earths (even if it is allowed in the regs) can end up with an install looking like the inside of a pin ball machine!
[/quote]

Agreed. That is why I keep it all separate. It makes testing installed circuit impedances much easier when the install has to be signed off..

Anyway I don't want to get in to an argument. Especially on this forum. Perhaps I should have said, in my original post, No You shouldn't instead of No you can't.

Peace  [:)]
[/quote]

Agreed, "I haven't, so I won't", to precis Magnus in a rather inverted manner[:D]

I'm sure it's not the conduit diameter that's the problem, I very carefully followed the instructions in my book for number, and size of cables per conduit, and I APPEARED to have loads of room.

So I did..........until it came to persuading the very stiff French cables round corners.[:P]

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I have a tip for pulling cables through gaines, in fact two!

The first is to pull the cables through before running the gain through partitions etc, or indeed to use "gaine prefilee".

The second is regarding the difficulty of pulling the cores through the gaine which tends to bunch up and create curves which further hinder efforts. - Tie off the one end of the draw-wire to a door or window handle, the other end secure to the cables and then pull the gaine over them, in this manner the cables are stretched into a staright line and the gaine is extended and straightened as it passes over them.

My business for some 10 years in the Uk involved a lot of cabling in ducts (gaines) and in all that time I never cottoned on to this, I found it in onew of my french electrical books.

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[quote user="J.R."]

I have a tip for pulling cables through gaines, in fact two!

The first is to pull the cables through before running the gain through partitions etc, or indeed to use "gaine prefilee".

The second is regarding the difficulty of pulling the cores through the gaine which tends to bunch up and create curves which further hinder efforts. - Tie off the one end of the draw-wire to a door or window handle, the other end secure to the cables and then pull the gaine over them, in this manner the cables are stretched into a staright line and the gaine is extended and straightened as it passes over them.

My business for some 10 years in the Uk involved a lot of cabling in ducts (gaines) and in all that time I never cottoned on to this, I found it in onew of my french electrical books.

[/quote]

Good tips.  Trying to pull cables through a fitted conduit , even if its a reasonable straight run is a non starter.  If you do manage to get the cables through, you will probably have damaged them in doing so.
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