David Jenkins
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| posted on 24/2/21 at 11:03 AM |
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Quick bit of advice from an electrician would be useful...
I am about to wire up a dawn-to-dusk switch and an external light into the garage lighting circuit. I have no fears or concerns about the circuit
I'll be using, nor about safety - I have been dealing with high-voltage electrics for a very long time (before anyone says anything!).
I have an easy access point to the garage's lighting circuit, the external light is easy (double insulated), but wiring the switch is making me
scratch my head - not because I don't know how to wire it (it's easy), but because it requires 3 wires. It's also double-insulated,
but it uses neutral, permanent live and a switched live connections.
So I have 3 wires to deal with, none of which are earth. So twin and earth seems to be unsuitable, and 3-wire and earth is excessive (I will only
need 750mm max length to the junction box, and it comes in big expensive reels!). I was thinking of running 3 individual cable cores, blue, brown and
either brown with a bit of red sleeve for the switched live, or some red cable core of the same diameter stripped out of another cable). The
down-side to this is that I would have 3 individual cable cores going into the side of the 4-way junction box. (Note: the switch's cable is
contained in a flexible conduit from the outside world).
A more fiddly solution would be to fit a junction box that has rear-entry for the switch's wires, but (a) I haven't got one, and (b)
I'm not sure what type to get.
So how would a proper certified electrician do it?
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daviep
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| posted on 24/2/21 at 11:44 AM |
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Sorry I'm not an electrician either but my thoughts are that I would just use 3 core and earth, as that is most likely how a tradesman would do
it, you don't mention what size of cable you require but almost all cable is available on eBay by the metre.
Alternatively I would use a piece of 3 core appliance flex and use heat shrink tube to sleeve the ends of the earth insulation to a different colour,
probably grey, black or red depending on what I had.
Regards
Davie
“A truly great library contains something in it to offend everyone.”
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David Jenkins
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| posted on 24/2/21 at 01:42 PM |
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About a year or so back I got a local electrician in to replace the consumer unit as it was too small for my needs. At the same time he went through
the house and re-wired all of the 'orrible bodge jobs that had been done over the years (not by me!).
Because of this I want what I'm doing to be 'to the book' as far as possible - I don't want to add a new bodge, even if it
works! He's a friend of mine, so I don't want to get my ear bent if it isn't up to his standards... 
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SteveWalker
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| posted on 24/2/21 at 01:51 PM |
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You can buy 4-core flexible cable by the metre from many places - or 3-core and Earth flat cable, but you'll need to seal that properly at the
cable entry and perhaps cover with split, flexible conduit to protect from the sun.
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David Jenkins
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| posted on 24/2/21 at 02:32 PM |
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quote:
Originally posted by SteveWalker
You can buy 4-core flexible cable by the metre from many places - or 3-core and Earth flat cable, but you'll need to seal that properly at the
cable entry and perhaps cover with split, flexible conduit to protect from the sun.
Trouble is, many places that would sell cable by length are shut at the moment - all the places like Screwfix and so on only do fixed lengths. I
might investigate eBay...
The only bit of cable that could be exposed to the sun comes down from the dusk-to-dawn switch, and that will have unsplit flexing conduit (already
got it, plus the gland to hold it in place and keep it waterproof).
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indykid
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| posted on 24/2/21 at 02:34 PM |
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As above, 4 core 3phase flexible cable is available cheap in short lengths on ebay. A local electrical wholsesaler should sell it by the metre
too....if there are any left by you.
The 3 phase flexible cable is also round so far easier to terminate in a standard gland.
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David Jenkins
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| posted on 24/2/21 at 02:43 PM |
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quote:
Originally posted by indykid
As above, 4 core 3phase flexible cable is available cheap in short lengths on ebay. A local electrical wholsesaler should sell it by the metre
too....if there are any left by you.
The 3 phase flexible cable is also round so far easier to terminate in a standard gland.
I went off and ordered some from eBay - 1 metre at £2.40 - hell of a lot cheaper than buying a 25 metre reel! Means that I'll have to wait
until the end of the week before I can do the job, but that's no real problem.
No problem with the gland - the flexible conduit is a perfect fit.
Is there a convention for which colour does what in 4-core cable? It's brown, black & grey - I guess brown = unswitched live, black =
neutral, grey = switched live? I can always put some red sleeving over the grey to indicate its status (liable to be a live circuit). I have the
sleeving on my shelf...
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SteveWalker
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| posted on 24/2/21 at 03:28 PM |
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Brown black and grey is for 3-phase and the colours all denote live. You should really sheath the black in blue, to give you a brown permanent live,
blue neutral and grey switched live. Although not the recommended way, even blue insulation tape is enough.
No need to sheath the grey in red, as grey means live anyway.
If your existing wiring is all in red and black, you are supposed to add a sticker (I can't really see the point in a single phase domestic
dwelling with no singles) to the consumer unit, stating the use of mixed colour systems.
[Edited on 24/2/21 by SteveWalker]
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roadrunner
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| posted on 24/2/21 at 04:13 PM |
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quote:
Originally posted by David Jenkins
I have been dealing with high-voltage electrics for a very long time (before anyone says anything!).
Sounds like my marriage 
[Edited on 24/2/21 by roadrunner]
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David Jenkins
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| posted on 24/2/21 at 04:50 PM |
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quote:
Originally posted by SteveWalker
Brown black and grey is for 3-phase and the colours all denote live. You should really sheath the black in blue, to give you a brown permanent live,
blue neutral and grey switched live. Although not the recommended way, even blue insulation tape is enough.
No need to sheath the grey in red, as grey means live anyway.
If your existing wiring is all in red and black, you are supposed to add a sticker (I can't really see the point in a single phase domestic
dwelling with no singles) to the consumer unit, stating the use of mixed colour systems.
Good info, many thanks.
I have old and new wiring, so brown/blue and red/black. I bet there isn't a sticker on the consumer unit!
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cliftyhanger
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| posted on 24/2/21 at 05:09 PM |
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quote:
Originally posted by David Jenkins
quote:
Originally posted by SteveWalker
You can buy 4-core flexible cable by the metre from many places - or 3-core and Earth flat cable, but you'll need to seal that properly at the
cable entry and perhaps cover with split, flexible conduit to protect from the sun.
Trouble is, many places that would sell cable by length are shut at the moment - all the places like Screwfix and so on only do fixed lengths. I
might investigate eBay...
The only bit of cable that could be exposed to the sun comes down from the dusk-to-dawn switch, and that will have unsplit flexing conduit (already
got it, plus the gland to hold it in place and keep it waterproof).
Teh electrical wholesalers I use sell by the metre (CEF and TLC, so I expect others do too)
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coyoteboy
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| posted on 24/2/21 at 05:30 PM |
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I still have a fuse-wire CU from 1930, protected by a whole-house RCD.
You're making me want to go and sort it 
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nick205
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| posted on 24/2/21 at 05:52 PM |
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quote:
Originally posted by coyoteboy
I still have a fuse-wire CU from 1930, protected by a whole-house RCD.
You're making me want to go and sort it
We had a fuse wire CU when we bought this house in 2004. A conservatory and some other electrical work demanded a change to update the CU. It works
very well and IIRC cost about £400 to have it changed.
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David Jenkins
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| posted on 24/2/21 at 07:27 PM |
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For me, it was having a car charger installed... there weren't enough spaces left on the CU, and it all had to be rearranged anyway as its
layout was non-standard.
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SteveWalker
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| posted on 24/2/21 at 10:06 PM |
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I put in a new CU when I re-wired here, before Part P. At the time a single, whole house RCD, covering sockets, cooker, garage and immersion was
pretty standard (no electric shower here), with lights and alarm unprotected. I have since removed the RCD and upgraded the protected MCBs to RCBOs to
prevent nuisance trips from the large number of leaky IT devices that we have. I will get round to upgrading the lighting MCBs soon.
The great thing was that knowing people in the industry, I got free samples - sockets, switches, pendant lampholders, ceiling roses, shaver socket,
cooker switch, all free (Volex 9000 range) and a free CU, MCBs and RCD (Crabtree Starbreaker), plus even some cable. So it cost me next to nothing!
Using 25mm2 T&E, with almost all of it in free air, for the cooker may have been overkill!. Yes, I know 25mm2 T&E (especially with Brown/Blue
cores in 1993) was not normal - that's why it was free. They'd accidentally produced almost a mile of non-standard cable before
they'd realised and stopped production!)
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