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p111dom

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Picked up a bathroom fan with some others items at a auction. It's in as new condition apart from the wire which had had its white shroud stripped down most of the wire exiting the cable. Just needs a new cable wiring in but it's a double live single neutral cable that I can't find anywhere. Is there a special name for this?
 

p111dom

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Correct Jonzjob. Ones a constant live and the other lives for a switch from say the bathroom light. All plastic body, two browns and a blue. Just can't find a cable with two browns and a blue.
 

nev

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The green and wetter end of the M4.
just use a length of this from the bathroom ceiling rose to an isolator switch and then to the fan. using tape or heatshrink or sleeving of the appropriate colour over the black and grey to identify them as live and neutral.
or run a twin brown and a single blue.
 

Eric The Viking

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The two lives are so that the timer allows the fan to run after the light switch controlling it is switched off. If you aren't bothered by that, you can join both live wires together safely inside the fan enclosure, connect it up with normal twin+earth (wired normally) as if it was a light bulb and it will just go on and off with the light, ignoring the timer.

Cheers, E.
 

p111dom

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Would do but there is no earth on the unit so don't want to add an additional wire in a redundant earth. If it's just heat shrink Id use I'll just use standard twin and earth heat shrinking the earth to a live colour.
 

Eric The Viking

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p111dom":2qs04yhl said:
Would do but there is no earth on the unit so don't want to add an additional wire in a redundant earth. If it's just heat shrink Id use I'll just use standard twin and earth heat shrinking the earth to a live colour.
It's not a good idea for a number of reasons:
  1. The earth is there to force a fuse to blow (or an RCD these days) if the cable is damaged. If that didn't happen fires and electrocution could result. It's important to have earth continuity all along the cable, to ensure the fuse blows if the cable is severed, especially with lighting circuits, where the wiring often takes quite strange routes. It's why an earth terminal is provided in lighting fittings, even though it's not always connected to the light itself. It gives you a tidy termination for the earth and a point to join it if it continues onwards.
  2. There is only the outer insulation covering the earth wire. That can degrade over time, for example in the presence of the styrene fumes given off by some insulation. In that case you have a live wire exposed, and worse, one that looks like an earth.
  3. People follow on after you. They expect to find things done in a certain way. Wiring in a way that's confusing is somewhat dangerous - pros are used to finding all sorts of bodges, but amateurs often make assumptions that could kill them! The only generally used way that T+E is installed, where the wire colour doesn't go as per, is a light switch or similar, where the blue (or black in old colours) is the switched live. In all such cases it should be identified by coloured tape or heatshrink at both ends, on the 'abnormal' wire. Personally, I also write on joist boxes (round junction boxes) what the circuit is, and any oddities (lighting sometimes has 'borrowed' neutrals, but it's deprecated these days (17th Edition distribution boards won't work properly if you do this). Labelling does no harm, as long as it's right!

You can get five-way (usually white) flex from plumbers, as it's used for solenoid valves in heating. It ought to be easy to blag a bit off your local heating engineer. Ignore one core and cut it off to the same length as the outer insulation.

You can also buy three-core+earth in short reels (25m), as it's also often used in hall/landing light switching, where there are switches for each light on the other floor, also for PIR security lamps.

Regards,

E.
 

p111dom

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That makes sense about the earth I guess. Was just going off a Sparky at work who failed an item (granted portable) because it was a self/internally insulated electrical item but someone had at some point fitted it with a triple core cable and done just that, snipped the earth off in line with the shroud. I guess his position was that if a live cane loose and came into contact with the earth it would have the same effect as you described. Ultimately for all these reasons I was trying to replace like for like. The OEM was a twin brown and single blue in a shroud, no confusion there, no heat shrink and if the shroud degraded anywhere along the cable the correct warnings/colours would be exposed. To be honest it's not like I'm going to use it myself. It's just in too good a condition to throw away but don't want to sell it on with a damaged cable. Currently there's just two browns and a blue loosed out of the unit so if I'm using heat shrink I think the best thing to do would be to but heat shrink over the lot effectively re-shrouding the wires to get the cable I'm looking for. Any problem with this?
 

Eric The Viking

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Personally, if I was going to sell it on, I'd just test it, to see that it works and isn't obviously going to blow up, etc. and then remove the cable altogether, leaving it for the purchaser to do. When selling, label as tested as working but s/h and with no warranty, nor safety checks (although it's implicitly safe if installed as intended). They aren't sold with wires attached normally.

I think the wiring is a can of worms you don't necessarily need to open ;-)

E.

PS: I think your sparky is very wrong: if loose live wires blow fuses or trip breakers, that's a GOOD thing, not a bad one!
 
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