Is it worth adding additional cores when buying SWA?

[Ivor Windybottom]

One possible use for additional cores could be a smoke alarm power supply and/or interlink to the house.

A doorbell?

It's no good for internet/network as it's the wrong cable and in very close proximity to the power.

It's not a bad idea to pop a few extras in for futureproofing.

 

[JohnW2]

Was the ducting big enough? Tight corners on the ducting

In at least some cases it's certainly been more than big enough, with no significant bends of any sort.

My most recent experience was with a ~30m run of ~4" diameter almost totally straight 'ducting' going across a part of my garden,which contained just three modest cables (plus a draw string). In the end I had to pull out all three cables (plus the drawstring), together, t,pulling a new draw string in behind them, and then using that string to pull all three cables, plus a new one, back in. When removed, I could see that the string was comprehensively wound around the cables for much of the run.

As I wrote,the problem seems top be that if one simply initially pulls in the cables (plus a draw string) in by pulling with another draw string, then there is seemingly no way of preventing the rotation of 'the bundle' which results in thee drawstring becoming 'wound around' the cables. Ironically,this is probably less of a problem if the duct is only just big enough for the cables!

was the draw cord made of?

I'm afraid I can't remember - probably polypropylene 'rope'.

Never struggled with this myself

I'm pleased for you,but that doesn't alter my personal experiences.

 

[JohnW2]

I've not had a problem either, but it does help to keep them separated on the input.

Particularly when it's a long run, I'm not sure that keeping them separated at the 'input' will have much impact on what happens downstream when one starts pulling.

It's also possible to blow or suck draw cords through after, starting with a light weight one that you use to pull a heavier cord through, driven by a blockage such as a carrier bag. Depending. The size of the duct you may get away with even a domestic hoover or compressor

I have, in my time, tried those techniques, with varying success.

Kind Regards, John

 

[d000hg]

I have certainly heard the same thing can happen. It's one of the reasons I write this thread - I previously naively assumed you can just pass another string/wire when pulling the cable, but the person who laid some other ducting/SWA for us a few years back told me they had had bad experiences "you only get one shot at this". Of course you can pull the cable back out but only if both ends of the duct remain easily accessible.

The ability of cables and string to tie themselves up seemingly despite you even touching them is well-known though, e.g. you put a cable away and it comes out tangled next Christmas

A guide rope only needs about 1/2 turn wrap on your SWA and the friction might make it unusable - it doesn't need to be wrapped round and round.

 

[bernardgreen]

As I wrote,the problem seems top be that if one simply initially pulls in the cables (plus a draw string) in by pulling with another draw string, then there is seemingly no way of preventing the rotation of 'the bundle' which results in thee drawstring becoming 'wound around' the cables. Ironically,this is probably less of a problem if the duct is only just big enough for the cables!

Twisted rope tends to untwist when under tension. This causes the cables to twist together.

Either use braided rope or fit a swivel link between rope and cables

 

[JohnW2]

Twisted rope tends to untwist when under tension. This causes the cables to twist together.

That's probably true, but not something I've ever experienced. I've never seen significant 'untwisting' of rope' Indeed, because I had also considered that possibility I've also tried with 'monofilament' pullcords (washing line!) and have experienced the same problem.

I'm not talking about anything 'untwisting' but ,rather,, of the (still 'twisted') 'cord getting 'wound around' the cables.

 

[JohnW2]

A guide rope only needs about 1/2 turn wrap on your SWA and the friction might make it unusable - it doesn't need to be wrapped round and round.

Exactly - that's my point - and with the recent example I described, there were many turns of 'wrap'

Kind Regards, John

 

[robinbanks]

Particularly when it's a long run, I'm not sure that keeping them separated at the 'input' will have much impact on what happens downstream

I don't see how this is possible; two wires are admitted into a duct at the same time and pulled and efforts to prevent them from overlapping are made at each end (and neither end twists as it feeds in/out), they cannot twist around each other, because for every twist "up", you need a twist "down", and even if two cables were internally twisted so as to encourage a coiling in a particular direction the entire cable would coil in that direction, not half one way, half the other

Draw cords work, because the pulled wire takes the same path as the cord, but a wire and a cord tied at the head and not twisted at the input cannot end up with one spiralled around the other for the full length of the run unless a twisting has been introduced. If only one wire is being drawn it doesn't end up twisted around the others already in the duct..

you put a cable away and it comes out tangled next Christmas

Either put away or got out incorrectly. Next time consider packing it how rescue workers pack throw ropes into a throw bag - about 2:30 in this video

.
If winding it onto a drum, unwind it off the drum rather than pulling off in one gonna bunch of coils and hoping the coils will uncoil without wrapping up - your extension reels don't generally knot up, thanks to the wind/unwind process

 

[JohnW2]

I don't see how this is possible; ...

I cannot argue about what you can 'see', but I can only report what I have experienced, many times.

two wires are admitted into a duct at the same time and pulled and efforts to prevent them from overlapping are made at each end ....

I'm not quite sure what you mean by 'overlapping' but, whilst one can exercise some control as regards what goes on at thee 'input' end, I can;t see what 'efforts' to control them can bee exercised at the other end, as it disappears into, as in my example,a 30mlog duct.

(and neither end twists as it feeds in/out), ...

... that, I presume is what happens. That whilst one can prevent 'twisting'at the 'input',one has no control about what happens at the other end, deep within the duct. In fact, somewhat ironically, the problem might reduce if one did not try to prevent twisting at the input, since the cable there then might 'follow' the rotation of the more distant bits, at least to some extent, reducing the extent to which the cord 'wound around' the cables.

It would be different if one were pulling the cables (and draw cord) through with something fairly 'rigid', that could largely prevent rotation of the far end of the cable+cord bundle,but when one is pulling with 'a bit of string',one has no control over rotation. Why thee rotation happens, I don't know - but I suppose that if the downstream end of the cables touch the wall of the duct at an angle as they are pulled, that might tend to initiate a rotation which then persist and becomes self-perpetuating?

However, I have not thought too deeply about the mechanism of hat happens, but I do know what has happened to me on more than a small number of occasions over thee decades.

 

[d000hg]

It'd be interesting (well sort of) to see this in a clear conduit. Because we all know a SWA does not twist or rotate easily at all, it’s pretty stubborn. It’s a bit of a mystery how a rope can get several wraps around it but it seems that happens.

 

[d000hg]

] .
If winding it onto a drum, unwind it off the drum rather than pulling off in one gonna bunch of coils and hoping the coils will uncoil without wrapping up - your extension reels don't generally knot up, thanks to the wind/unwind process

you’re definitely right there. wrapping a cable onto a spool introduces a huge amount of twist compared to rolling it.
I’ve learned that in the past

 

[JohnW2]

It'd be interesting (well sort of) to see this in a clear conduit. Because we all know a SWA does not twist or rotate easily at all, it’s pretty stubborn. It’s a bit of a mystery how a rope can get several wraps around it but it seems that happens.

I can't disagree with what you're saying. However, although the OP of this thread is admittedly about SWA, the comments I've been making have been 'general', and many of the problems I've personally experienced have been related to cables other than (and 'softer' than) SWA

 

[Notch7]

I am not sure I even understand the question properly we have an old dedicated overhead cable running 100m up our drive from the road (just to our house) and a brand new meter/supply was fit ~3 years ago off the pole (they replaced the cable to the meter and everything). We have the main consumer unit coming off that which has an earth rod sunk into the ground on the exterior wall of the building (so it is accessible).

different earthing types:

chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://electrical.theiet.org/media/1549/earthing.pdf

you might need to one of the cores rather than the armoured sheath as an earth

and some electricians prefer it as they they feel the armour can rust away if the outer plastic is damaged -seems like theres differing schools fo thought on it

 

[robinbanks]

one has no control about what happens at the other end, deep within the duct.

Maybe you and I have different things in mind when we each say SWA, but the armoured cable I'm thinking of would be impossible to twist to any meaningful degree if unrolled. If pulled sideways off the coil and straightened out it would have to twist to remove the loop because there is no way it would rearrange itself internally to absorb the rotation brought about by straightening of the loop

 

[OvertonPlumber]

I had 42mtrs of 16mm swa run down to my garage. Had a 100 amp. Cu in there with a 16amp socket for my inverter tig welder. Ran the wifi down the armored with a tplink main plug worked a treat.