≥6-core flex?

[JohnW2]

If your scaling is anywhere near correct (it looks to be in the pic) I wonder why you are not looking at staying with 3C&E

The scaling is pretty accurate, but it is, of course, based on the dimesnions of flat cabled, which varying quite a bit.

As for your question, maybe your experiences are very different from mine - but it would seem 'obvious' to me that it would be very much more difficult(if not impossible!) for me to try to to run two flat cables, side by side, with 'all four corners' touching, or nearly touching, the walls of the conduit, than to have just a single, round cable not much bigger than half the ID of the conduit, almost 'floating around' within the conduit (probably not touching the conduit in more than one place).

In fact, I could make life even easier for you since, at least in terms of my present requirements, I wouldn't need 2 x 3C+E - one 3C+E and one T+E would suffice at present.

 

[mikehammer69]

No need for that - 1.0 mm² YY (which is 'allowed') is only fractionally larger but, electrically speaking, totally unnecessary for supplies to two LED lights

The concern always with undersized fixed wiring is what happens after

I appreciate the 1mm complies

 

[SUNRAY]

The scaling is pretty accurate, but it is, of course, based on the dimesnions of flat cabled, which varying quite a bit.

As for your question, maybe your experiences are very different from mine - but it would seem 'obvious' to me that it would be very much more difficult(if not impossible!) for me to try to to run two flat cables, side by side, with 'all four corners' touching, or nearly touching, the walls of the conduit,

The reality in my experience is keeping the cable flat/straight/smooth during the pull-in allows them to slide in fairly easily just as you describe.and of course much easier if Mrs JohnW2 is as handy as Mrs Sunray in assisting with these matters.

than to have just a single, round cable not much bigger than half the ID of the conduit, almost 'floating around' within the conduit (probably not touching the conduit in more than one place).

Yes of course and I have indeed done something very similar on a number of occasions, without full details of the job (which I wouldn't dream of asking or expecting from you) I'll assume this will entail requiring adding some form of junction box which may not otherwise be required.

In fact, I could make life even easier for you since, at least in terms of my present requirements, I wouldn't need 2 x 3C+E - one 3C+E and one T+E would suffice at present.

That would of course simplify the matter. Are you implying there may be future developments here, if that is the case I'd be looking for more at this point, a 12*1 is still only 11.1mm, I know I have some 18*1.5mm² which would happily be able to wend its way but from that chart is 15mmØ so I imagine a non starter.


My first action would be to slide a cable rod into the space beside the existing cable and see how easily is goes in, you may be surprised.

 

[JohnW2]

The concern always with undersized fixed wiring is what happens after

Someone always says that, but in this case it seems just plain silly! What on earth could happen in the future to require the cable feeding two light switches to be 'massive'?

In any event, what we're talking about is worse (sillier!) than that since 0.75 mm² flex in NOT, electrically speaking.'undersized', since wth a CCC of 6A, it's adequately protected by the 6A OPD of a lighting circuit. The only thing it is (may be!) 'under' is some ('inexplicable') seemingly arbitrary 'minimum cable size'.

Until very recently, we had the same nonsense with 'power' (as opposed to 'lighting') circuits which had an arbitrary minimum cable size of1.5 mm², even thiose the CCC og 1.0² mm cable would be adequate in some situations. However, they have 'seen the light'over that one, and there is no longer a distinction bewteen 'power' and 'lighting' circuits, the minimum therefore now being 1.0 mm² for both.

I'm not convinced that the people who write these regs ever both to read what they have written before 'publishing'it

 

[JohnW2]

The reality in my experience is keeping the cable flat/straight/smooth during the pull-in allows them to slide in fairly easily just as you describe.and of course much easier if Mrs JohnW2 is as handy as Mrs Sunray in assisting with these matters.

You seem to have had much happier experiences than me. It's keeping things perfectly straight/flat which is the issue - the slightest tendency to bend, let alone 'twist', and everything often 'jams up' (in my hands)

Yes of course and I have indeed done something very similar on a number of occasions, without full details of the job (which I wouldn't dream of asking or expecting from you) I'll assume this will entail requiring adding some form of junction box which may not otherwise be required. .... That would of course simplify the matter. Are you implying there may be future developments here, if that is the case I'd be looking for more at this point, a 12*1 is still only 11.1mm, I know I have some 18*1.5mm² which would happily be able to wend its way but from that chart is 15mmØ so I imagine a non starter.

This whole discussion has now actually become pretty moot (see below) but my very simple question about availability of a certain type of cable seems to have turned into a complex 'big deal'

There are certainly no secrets. The present switch, supplied by 3C+E is just inside the front door,and does 2-way switching of the hall lights, the other 2-way switch being on the first-floor landing. I'm about to install a light outside the front door, very close to that switch and simply want to change the existing switch to a 2-gang one so it can control the new light as well as the existing one (and I obviously need to get L&N for the new light down to that vicinity. It it extremely unlikely that there will be any 'future developments' that would need any more wiring in this location in the house.

However, I've been silly (I blame a combination of old age and the unacceptable heat ). I've just realised the the present 2-way switching of the hall lights has been done in the 'modern'('conversion') way, such that one of the strappers is a 'permanent live. That means that all I need (in addition to what's there already)is a neutral (which I'm pretty sure is available very nearby to the top of the conduit) in order to be able to install the new outside light and a switch (gang) for it. So it looks as if all I need to do is replace the exisiting3C+E with 5-core flex ('4C+E), of which I have plenty, and which hopefully will/would be a fairly straightforward 'change'! The situation would then look something like this (or am I missing anything?!) ...

My first action would be to slide a cable rod into the space beside the existing cable and see how easily is goes in, you may be surprised.

That's been one of my concerns, since I did a little playing with just one 1mm² insulated conductor (from some T+E) and struggled to get it in at all beside the existing cable

 

[securespark]

What I have done in the past is strip twin and earth and pull the stripped portion down the 5/8" conduit, such that the sheath is just inside the conduit. You'll need little rubber thingies on the ends though, if you haven't got them already.

I don't know if modern ones exist.

 

[JohnW2]

What I have done in the past is strip twin and earth and pull the stripped portion down the 5/8" conduit, such that the sheath is just inside the conduit.

It seems that that is what's been done- as you can see from my photo, the sheath is not visible at the bottom of the conduit, and nor can I get it to show itself by gentle pulling (I'm hesitant to do more than that until I'm ready to deal with any undesirable consequences!)

You'll need little rubber thingies on the ends though, if you haven't got them already. I don't know if modern ones exist.

What are/were these thingies -some sort of grommets?

 

[securespark]

Yes.
Like a sleeve of rubber that went over the end of the conduit that prevented the cable from chafing on the metal.

I don't know if I still have any to photograph and show you. I'll have a look.

 

[JohnW2]

Yes.
Like a sleeve of rubber that went over the end of the conduit that prevented the cable from chafing on the metal. ... I don't know if I still have any to photograph and show you. I'll have a look.

Fair enough, but if it were going to be able to prevent 'chafing, it presumably would have to at least slightly 'into' the conduit, which could be an issue if, aspeople have been discussing, one is trying to cram a lot of cables into the conduit?

... and, anyway, why should chafing occur after the cable has been pulled through -nothing is going to 'move' significantly, is it?

 

[securespark]

Hopefully not too much.

But one still fits grommets elsewhere to stop cable rubbing.

Cables do move a little when you take off or swap out the accessories they are attached to and cables in straight conduit drops will be free to move throughout their length.

I used to try and collect the old grommets and whenever I reused old 5/8" conduit, I made sure I used them on each end.

It was a bit of a faff, because there were usually wooden boxes and the conduit entered in the middle. So I'd end up drilling a 20mm hole in the middle of the new box and fixing it such that the conduit just came inside.

 

[SUNRAY]

You seem to have had much happier experiences than me. It's keeping things perfectly straight/flat which is the issue - the slightest tendency to bend, let alone 'twist', and everything often 'jams up' (in my hands)

I have the T-shirts too

This whole discussion has now actually become pretty moot (see below) but my very simple question about availability of a certain type of cable seems to have turned into a complex 'big deal'

There are certainly no secrets.

I didn't expect there but from history your on here I don't expect to question your reasons for the work or your understanding of it.

The present switch, supplied by 3C+E is just inside the front door,and does 2-way switching of the hall lights, the other 2-way switch being on the first-floor landing. I'm about to install a light outside the front door, very close to that switch and simply want to change the existing switch to a 2-gang one so it can control the new light as well as the existing one (and I obviously need to get L&N for the new light down to that vicinity. It it extremely unlikely that there will be any 'future developments' that would need any more wiring in this location in the house.

Only mentioned due to this casual comment:

...at least in terms of my present requirements, I wouldn't need 2 x 3C+E - one 3C+E and one T+E would suffice at present.

However, I've been silly (I blame a combination of old age and the unacceptable heat ). I've just realised the the present 2-way switching of the hall lights has been done in the 'modern'('conversion') way, such that one of the strappers is a 'permanent live. That means that all I need (in addition to what's there already)is a neutral (which I'm pretty sure is available very nearby to the top of the conduit) in order to be able to install the new outside light and a switch (gang) for it. So it looks as if all I need to do is replace the exisiting3C+E with 5-core flex ('4C+E), of which I have plenty, and which hopefully will/would be a fairly straightforward 'change'! The situation would then look something like this (or am I missing anything?!) ...

View attachment 418299


That's been one of my concerns, since I did a little playing with just one 1mm² insulated conductor (from some T+E) and struggled to get it in at all beside the existing cable

I find a single copper wire tends to catch and then buckle at the slightest hint of any obstruction.



FWIW I have just been playing with a microphone stand top section which has a 5/8" thread. It measures 15.88mm & 13.63mm so I'll estimate fairly close to 5/8" or 16mm conduit.
This scrap of 1.5mm² 3C&E looked like this

complete with lumps as shown after removing it from here

It pushed in and pulled out without using force to its 300mm length but probably wouldn't have done so over say 2m. Smoothing out the bumps just a little

it slid in and out with ease.

I'll repeat this is not actual conduit so I don't know how close the dimensions are, nor do I know if your installation is either of 5/8" or 16mm conduit, for all I can tell from here it could be 1/4" gas pipe.

 

[JohnW2]

I have the T-shirts too

I would be very surprised if you didn't.

In my experience, the situation I have at the moment exemplifies the most common problem - at least IF I pull the new cable(s) in from the bottom. As you can see from the photo (and this must be extremely common) to get a new cable into the bottom of that ('sunken') conduit would require a significant bend immediately before it entered the conduit and, as the cable moved into the conduit, the bend would 'propogate upwards, very often resulting in a 'jamb'.

I suppose I could first pull in something easy (like a bit of string) from the bottom (pulling it with the existing cable), and then use that 'something' to pull the new cable in from the top (where,in my present situation, the same problem does not exist, so the cable could enter the conduit 'straight').

However, it's not at all uncommon (probably very common) for this problem to exist at both ends of the conduit, in which case there is presumably no way of circumnavigating it ?!

 

[SUNRAY]

I would be very surprised if you didn't.

In my experience, the situation I have at the moment exemplifies the most common problem - at least IF I pull the new cable(s) in from the bottom. As you can see from the photo (and this must be extremely common) to get a new cable into the bottom of that ('sunken') conduit would require a significant bend immediately before it entered the conduit and, as the cable moved into the conduit, the bend would 'propogate upwards, very often resulting in a 'jamb'.

I suppose I could first pull in something easy (like a bit of string) from the bottom (pulling it with the existing cable), and then use that 'something' to pull the new cable in from the top (where,in my present situation, the same problem does not exist, so the cable could enter the conduit 'straight').

However, it's not at all uncommon (probably very common) for this problem to exist at both ends of the conduit, in which case there is presumably no way of circumnavigating it ?!

Yes I understand exactly and in simple terms exists at every Besa box.
The difference is learning to manage it. I pretty much always strip insulation from the leading end to make it as thin and tapered as possible and the transition from whatever means of pulling it in is used as smooth as possible, all with as little tape a practicable to avoid stiffening it.
Providing the 'bend' required isn't TOO sharp It sometimes takes a little preparation time but the success is usually worth it.

 

[JohnW2]

Yes I understand exactly and in simple terms exists at every Besa box. ... The difference is learning to manage it. I pretty much always strip insulation from the leading end to make it as thin and tapered as possible and the transition from whatever means of pulling it in is used as smooth as possible, all with as little tape a practicable to avoid stiffening it.

Sure, that is all crucial, and almost 'goes without saying'

Providing the 'bend' required isn't TOO sharp It sometimes takes a little preparation time but the success is usually worth it.

As I've said, you seem to have had happier experiences than me. In my hands, the 'bend' doesn't have to be remotely sharp to create the problem. Even a very slight bend results in the cable contacting and pushing aganst two 'opposite' points on the ID of the conduit, and it is that which I presume creates the friction which can result in jams.

 

[JohnW2]

This is very interesting/intriguing ...

People have been making all sorts of suggestions (about which I'm pretty nervous!) about getting umpteen cables/cores into the seemingly 'tiny' (maybe 5/8") conduit I'm dealing with, but it seems that whoever did the present wiring even had a problem getting one 1mm² 3C+E cable in!

I've now got that "3C+E" cable out, and drawn in a new length of 5-core flex. I commented before that I could not find he cable sheath at the bottom, so assumed it had been 'cut back', but there was no doubt that what was going into the top of the conduit was3C+E (with sheath). However, having now got it out, look what I found ....

.... There was, in fact, only one or two inches of sheath going into the top of the conduit. For the rest of the run down the conduit, the sheath had been stripped off, leaving just the cores (including the bare CPC), which were neatly taped together. I suppose that's not too far off Sunray's suggestion to"use singles", but I have to say that I've never previously seen it done in quite this way