Hahaha... rewired 100s' of old council flats', where the cooker runs' were the worst with old 7/044 VIR cables STUCK inside the conduit! BUT, pulling in 6mm singles, (ESPECIALLY when, back then, we'd sometimes been given SOLID 6mm, instead of stranded were another nightmare, haha),... glad I don't do that anymore BUT; answering your post... I always used lard etc, (don't tell anyone... sometimes fairy liquid, when desperate),  but you must use someone to pull, while you're, (I know you know what to do...), feeding, the cables' in BUT BUT, haha, when the draw wire separated, haha!  BUT , I hear you say... "what about the air gap?" WOT AIR, haha, GAP?

The other alternative is 2" x 2" metal trunking... I cannot remember, but must have at one point, used 32mm metal conduit, I can remember, actually, my foreman using a large section, around 5 foot long, of timber, with a hole at one end, used for bending metal conduit. I know I'd use the trunking, before using 32mm stuff. TOP tip; if you're running metal trunking and you've worked out you need to start off with 4" the always go one higher... use a 6" then drop down, at the first branch, to a smaller one!

Happy days', (on reflection). 

Wot a life, a? 

All the best! Tom

Tom, thank you for your unique response as ever.

If your VIR is stuck, it doesn't really matter if you pull hard enough, but then it occurs to me that if you have a Klingon left behind, drawing in the new cable could be difficult.

"draw wire separated" No problem if it is the first wire 'cos you can redo it.  I have been using some 3 mm string from Cotswold. It is a bit too stretchy for my liking, but far stronger than any pull that I can manage. I haven't lost control of the draw wire yet!

Chris Pearson said:

3 x 16 mm² into 25 mm conduit.

I think it's less of a function of the diameter of the conduit, more the lack of flexibility in the conductors themselves vs the bends (and also taking into account the radius of those bends, but even so, as has been said, more than a couple and it's difficult).

I seem to find for any given pipe and cable combo there is a critical distance up to which it is a piece of cake, beyond which it rapidly gets hard and then   much beyond 1.5 times that it becomes essentially impossible. Clever use of lubricant and draw tape with wheels etc helps change that distance, but there is still remarkably hard cut-off when the only method it to have mid-point access. But in general flexibles do go quite a bit further for the same nominal sizes.

Mike.

mapj1 said:

But in general flexibles do go quite a bit further for the same nominal sizes.

Agreed, I think that's the issue ... unless, of course, the live conductors are 6181Y (insulated and sheathed), there's plenty of space in there for thermal and space to bend/twist.

Looking at how much spare space there might be with the max diameters of cables and max thickness of conduit walls (assuming plastic, as the wall thickness is a little more), if you get one bend after another, it's not going to be easy due to the rigidity of the 16 mm² 7-strand:

I think that Graham is correct: irrespective of the diameter, the cables must touch the walls on the inside of any bends.

I think that once the cables have been drawn in so that there are 3 side by side, it is just a matter of effort. Part of the problem is exerting enough force whilst up a ladder, especially when going sideways. Kinks do not help.

The difficulty with the 3rd cable is that it presumably has to slide between the other two around any bends. If the cables get a bit twisted, it gets so much more difficult.

I have found that a couple of yards at a time is the maximum if any degree of control is to be maintained; which is why it's up the ladder, lube, down the ladder, move the ladder, up the ladder, pull, etc. Patience is the key!

Chris Pearson said:

The difficulty with the 3rd cable is that it presumably has to slide between the other two around any bends. If the cables get a bit twisted, it gets so much more difficult.

From experience, it's often easier to draw in a set of conductors with a draw wire, than an individual conductor after other conductors are already present, which perhaps supports this theory. However, I think also, the difference pulling a 1.5 sq mm vs a 16 sq mm in both instances will speak for itself - even if there is loads of room for either: the 16 sq mm will struggle round the bends (to bend itself) far more than the 1.5 sq mm.

Coming back to the cables' flexibility, getting 3 x 16 mm² to go round a bend together is a big ask. I tried it and I am simply not strong enough.

Getting it out afterwards without at least partly dismantling the conduit first will be at least as difficult.

Guidance Note 1, Appendix A, Tables A3 and A4 (or OSG Appendix E, Tables E3 and E4) provides us the following for 16 sq mm insulated (not sheathed) in 25 mm conduit:

• Straight run: 10 m  run should be OK
• One bend: 10 m run should be OK
• Two bends: 10 m run should be OK.
• Three bends: 4.5 m maximum run
• Four bends: 2.5 m maximum run

I think three and four bends would not be easy full-stop, with Class 1 (Solid) or Class 2 (Stranded / rigid) 16 sq mm conductors - perhaps a classic case of where practical experience wins over theory.

Another factor is that a typical minimum bend radius of H07V-R is 4 × diameter, or 28 mm for 16 sq mm - so a tight 90 elbow really won't do the job !

Hi Chris,

After going through the replies from the thread, here's my take:

1. Teamwork Makes the Dream Work: Simon and AJJewsbury are spot on. Whenever possible, get someone else on the other end. Pulling in thick cables can be a two-person job. It's all about the balance between feeding and pulling.

2. Conduit Size and Bends: Broadgage and Sergio got a point about the conduit size. But I get your point about space constraints. Sometimes, the ideal solution isn't always practical. Too many bends and even the recommended sizes can become a chore.

3. Alternative Methods: Andy's idea about threading individual lengths of conduit over the cables is clever. It's a workaround, but it might just do the trick in tricky situations.

4. Materials and Techniques: WHJohnson suggested SWA. While it may not have been ideal for your situation, it's good to have options. Mike and Tom shared some wild stories. Sometimes, unconventional methods can be lifesavers - like Tom's use of lard or fairy liquid, and Mike's coax inside a nylon 'suzie' pipe.

5. The Third Cable Conundrum: As you and Graham highlighted, the third cable sliding between the other two can be tricky. The twists, the bends – it's a whole other beast.

6. Bending Challenges: Mapj1 and gkenyon provided insights about the cut-off distance and bending challenges, especially when dealing with rigid cables.

7. Patience Is Key: Your comment about patience hits the nail on the head. It's a tough job, and it's all about taking it step by step. As you rightly said, demonstrating that the job is possible is what counts in the end.

Yes, the OSG might give guidelines, real-world scenarios can throw you a curveball. 

take it easy on yourself! It's a tough job, and sometimes, it's just going to be a grind.

Cheers,