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Topic Title: Not a borrowed neutral
Topic Summary: Neutral for a fan (domestic)
Created On: 16 October 2013 07:30 PM
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 16 October 2013 07:30 PM
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ady1

Posts: 766
Joined: 19 April 2005

Changed a board today and found the neutral from the unused shower cable was being used by the extractor fan.
Bizzare i know.
Upon thinking about it.....
If the earth is connected in too, then whats wrong with it ?
Your opinions pls

Regards
Ady

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Resistance is futile.
 16 October 2013 08:07 PM
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peteTLM

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and the live is from..........................?

If the live ISNT from the shower cable, of course its a borrowed neutral. Albeit it one from a radial not used for anything else.
Poor.

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----------------------------------------
Lack of planning on your part doesn't make it an emergency on mine....

Every man has to know his limitations- Dirty Harry
 16 October 2013 08:07 PM
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AJJewsbury

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If the "unused shower cable" isn't connected to any other load, nor the L to a different protective device, then it's just an expensive sheathed single-core N for the circuit that's supplying the fan. No objection to that - although it presumably needs labelling at the CU unless it manages to share the correctly numbered way in the N bar as the N for the rest of the circuit.
- Andy.
 16 October 2013 08:34 PM
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Parsley

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521.8.1 Each part of a circuit shall be arranged such that the conductors are not distributed over different
multicore cables, conduits, ducting systems, trunking systems or tray or ladder system.

Regards
 16 October 2013 09:50 PM
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ady1

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Just what I thought Andy.
Pete - The shower cable is otherwise un-used - yes it's poor, but I didn't do it.
Parsley - Excellent reg: I'm thinking now i should note that reg on my EIC in the departures box, but leave it as it is.
Needless to say, they don't want their bathroom ripping apart by me.

Agreed ?
Regards
Ady

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Resistance is futile.
 16 October 2013 11:05 PM
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AJJewsbury

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521.8.1 Each part of a circuit shall be arranged such that the conductors are not distributed over different
multicore cables, conduits, ducting systems, trunking systems or tray or ladder system.

I've still not quite figured out what they intended by that wording - 2-way switching without using different multicore cables? How about if you want to feed a fancy multi-lamp light fitting with three different switch lines? Are 6241Y/6181Y "spider wiring" for lighting banned?
- Andy.
 17 October 2013 07:21 AM
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leckie

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I have not got a clue what that regulation means.

Is it referring to line and neutrals from the same circuits not in different ferrous enclosures (eddy currents)?

Is a twin brown strapper and 6181Y switch line not allowed?
 17 October 2013 08:45 AM
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Parsley

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6181Y isn't a multicore cable.

EMI issues, induction loops and two way switches.

444.4.2.1 (iii) The installation of power cables (i.e. line, neutral and any protective earth conductors) close together in order to minimize cable loop areas.

Regards
 17 October 2013 02:43 PM
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davezawadi

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No, I think its to prevent inductive heating where the circuit conductors are enclosed in different metal enclosures, read conduit, swa, trunking (steel). What happened to the neutral travelling with the live to the fan?

It is a bit confusing, but probably won't cause any problem in a low power domestic fan case. Needs a note on your EIC though.

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David
CEng etc, don't ask, its a result not a question!
 17 October 2013 09:04 PM
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peteTLM

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I dont think its as high brow as eddy currents, more to do with preventing lash ups like the one the OP describes.

I read it as ' the circuit shall not contain conductors arranged within different containers'

E.g. you cant nick a spare core out of one cable for Live, and use another spare core in another cable for the neutral. They may be different lengths (like the op) different conductor sizes (like the op). You would expect the conductors supplying an item to be supplied to that item within the same cable.

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Lack of planning on your part doesn't make it an emergency on mine....

Every man has to know his limitations- Dirty Harry
 17 October 2013 09:24 PM
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leckie

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Ok, forget my ref to 6181Y, but how would mixing multicores, say 6243Y's in any arrangement on the same circuit be wrong, excluding routing cable line and neutral conductors through different, conduits, trunking, etc. or is that it, that's what the reg actually means?
 17 October 2013 10:58 PM
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Parsley

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Originally posted by: leckie

Ok, forget my ref to 6181Y, but how would mixing multicores, say 6243Y's in any arrangement on the same circuit be wrong, excluding routing cable line and neutral conductors through different, conduits, trunking, etc. or is that it, that's what the reg actually means?


I don't think it prevents using a 3 core and a 2 core or whatever on the same circuit, I see it as a circuits conductors should be kept close together by being in the same multicore cable(s) or in the same trunking/conduit single conductors for various reasons it's good practice and meets the requirements of 314.1, 314.4, 521.5.1 and 444.4.2.1 and probably several others.

Regards
 19 October 2013 06:50 AM
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leckie

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Oh I see Parsley. So with reference to multicore cables it would mean not for example, not using 2 cores from a three core cable for the strappers of one lighting circuit and the remaining core for part of another lighting circuit.

So what about a 4 core swa using 2 core for one single phase circuit and the other two for another single phase circuit? This isn't distributing circuits over different cables, but is more than one circuit within one cable. So that would be ok but you couldn't use three core for a three phase balanced load supply and the spare core for a conductor in another circuit.

With regards the op, the old shower supply isn't a circuit, it's a bit of cable with one core redundant, so it's not shared circuits within a multicore cable so it would seem ok. Although i can't imagine why you would send a line from a light to a fan and a neutral from a redundant supply? Perhaps the fan was changed to a timer version and had a twin and earth from the light and these were used for permanent and switched lines and they nicked the neutral from the spare cable. Cannot think of another scenario.

Edited: 19 October 2013 at 07:01 AM by leckie
 21 October 2013 02:48 PM
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AJJewsbury

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Is it referring to line and neutrals from the same circuits not in different ferrous enclosures (eddy currents)?

But that's already covered by (the old) 521.5.1.

EMI issues, induction loops

Again, as you say, already covered by 444.4.2.1 - so why do we need another regulation? Is EMI really affected by having a couple of thicknesses of PVC sheath between a couple of live conductors?

E.g. you cant nick a spare core out of one cable for Live, and use another spare core in another cable for the neutral.

My gut feel is that's the kind of thing they had in mind - but we have a long tradition of doing just that (e.g. a light fed with L+PE 6241Y and a separate N 6181Y) - and (although frequently not done), it would be possible to route cables in such a way that satisfied EMI requirements. Plus of course we are allowed to run two or more circuits in the same multicore cable, so it's all looking very muddy to me. And I've not even started to think about typical multi-zone central heating control wiring...

- Andy.
 21 October 2013 04:17 PM
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leckie

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I dont think it means a 6241Y and a 6181y is a problem; as parsley has already said a 6181Y is not a multicore cable. I think, for example, a 6243Y that used 2 cores for say the strappers of one circuit and the other core for a line, neutral or switch wire to another circuit would be the type of issue referred to regarding multicore cables.
 21 October 2013 04:21 PM
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leckie

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Having said that, a few posts ago I hadn't got a clue to what the reg. might mean!
 21 October 2013 04:42 PM
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AJJewsbury

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I dont think it means a 6241Y and a 6181y is a problem; as parsley has already said a 6181Y is not a multicore cable.

Sorry - I've caused more confusion than intended. 6241Y has one "live" core and a bare c.p.c. - hence multicore. I only mentioned 6181Y (one core insulated & sheathed - usually used for N) as the two were usually used together in "spider wiring" of domestic lighting circuits and the like.

I think, for example, a 6243Y that used 2 cores for say the strappers of one circuit and the other core for a line, neutral or switch wire to another circuit would be the type of issue referred to regarding multicore cables.

I think there are two points there - one is sharing a cable between two circuits, the other is having one circuit split between two cables. If it's just the latter, why is splitting a circuit across more than one multicore cable bad? Why is having two 2-core cables bad, but four single-core ones or even one 3-core and one single-core good? Has someone out there got shares in a company that's about to start producing 4-, 5- and 6-core BS 6004 cables?

- Andy.
 21 October 2013 04:53 PM
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leckie

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I don't think one circuit across more than one cable, either single or multicore is a problem. I think it's mixing circuits in one multicore that might be what the reg refers to, as per the example I used. However, we are allowed to use a four core swa for two single phase supplies I think, but that is two complete circuits, not a division of circuits.
 21 October 2013 05:19 PM
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AJJewsbury

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Yet the wording of 521.8.1 allows me to put L of three different circuits down one 6243Y and use three separate single cores for the corresponding Ns ? - or vice versa with the Ls in single cores, or even a mix ??
- Andy.
 21 October 2013 09:24 PM
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leckie

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Sorry Andy, I'm not reading it like that. Parsley explained it to me, and I thought I had got hold of the regulation. But I understood it was saying you could not mix individual parts of circuits in a multicore cable. I must still be misunderstanding it.

I think you can use several multicores to wire the same individual circuit, but not add 1 core into a multicore that is a different circuit.

Edited: 21 October 2013 at 09:33 PM by leckie
IET » Wiring and the regulations » Not a borrowed neutral

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