Advice re crimps and heat shrink please

[Mike Clarke]

I need to re-route some mains cables which squeeze through a hole alongside hot water pipes. I'm planning to remake the joints with insulated crimps and heat shrink sleeving.

I'll avoid the cheap 3 quid crimp tools and get a ratchet one, is there much to be gained by getting the £25 one from Screwfix as opposed to the £10.50 one from Toolstation?

Judging from the flexibility of the cables I think they are old 7/029 and 7/036. Will crimps grip OK on this or are they only suitable for modern metric stuff?

I intend to cut the individual conductors to different lengths to avoid bulky joints with all 3 crimps side by side. Am I right in assuming that I don't need to put sleeving over the individual (insulated) crimps but just over the complete cable to replace the PVC sheath? I was planning to use wide black heat shrink from Maplin for this, is it tough enough for the job?

This is my first time using heat shrink on mains cable. Previous jobs have been on small electronic bits where I just wiped the back of the soldering iron along the sleeving to shrink it. This isn't going to work for the big stuff, will a hot air gun be OK - knowing what it does to paint I'm a bit nervous about using it on PVC cable but SWMBO's hairdryer doesn't seem hot enough.

[chris French]

In message , Mike Clarke writes

I should imagine so.

I had some of that so used it, seems fine.

Yes, you don't need to sit there for long, or hold it too close to shrink it, the PVC insulation will be fine.

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[Richard Porter]

It's certainly worth getting a proper ratchet crimp tool. I think Maplin have theirs on offer at the moment. It's a lot less than £25 though that's what I paid for mine a few years ago. I haven't seen the Screwfix or Toolstation tools.

Most mains cable is now solid core. If you've got old rubber covered flexible stuff consider whether you should be replacing the whole lot. Either way, isn't it a lot easier just to use a junction box? You don't really want to be making the joints where the cable squeezes past the pipe. In any case that should be avoided as the heat will make the insulation brittle.

I would tape the joints and then tape the whole lot together if I was going to do it that way, but as I said I'd rather use junction boxes.

A hot air gun is fine, or a blowlamp if you're careful and don't get the flame too close. Use a plumber's soldering mat to protect surrounding paintwork. You won't need to apply heat for long enough to do any damage.

[:::Jerry::::]

7/029 and 7/036 multi-strand cable is not limited to old rubber covered / insulated stuff, there must still be some considerable quantity of PVC stuff around.

[Dave Plowman (News)]

A hot air gun for paint stripping will work fine. If you haven't got one, a two heat model will be best, and use the low one. You've still got to be slightly careful, but the shrinking happens long before the PVC melts.

[Mike Clarke]

This is PVC cable, it was introduced a few years before cables went metric.

That's what I would have done in the past but I now get the impression that crimps provide a better permanent joint than screw terminals, and these joints won't be very accessible afterwards.

Yes, that's why I intend cutting the cables, re-routing them to avoid the pipes and then linking them up again.

[The Natural Philosopher]

You know, why not solder it and heat shrink?

Crimps are ok for the sort of half trained gibbon that calls itself an electrician, but really...

[chris French]

In message , Mike Clarke writes

Isn't it a regs requirement now anyway that screwed joints be accessible?

Crimping is quicker as well than fiddling with junction boxes as well.

[Phil Addison]

Solder should not to be used as the mechanical support alone. If soldering the wires should be mechanical joined first, e.g. by several tight twists. The heat shrink is not adequate for mechanical integrity, only for insulation.

Crimps are one of the few methods approved for use in hi-reliability aerospace work. However, that only applies if a proper force-calibrated ratchet tool is used - and that excludes the el-cheapo £3.95 scissors rubbish. If you haven't done crimping before I should do a few trials first and make sure you cannot pull the finished joint apart with a straight pull.

Phil The uk.d-i-y FAQ is at

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[Richard Porter]

I've used crimp terminals quite a lot on cars. Yes they're quick but in my experience not as reliable as soldered terminals. Using the correct size terminals or butt connectors for the cable is crucial.

For joining multistrand cables I prefer to mesh the strands, solder and heatshrink. The heatshrink tube may have to be threaded onto the cable first! Of course you have to be able to make a good solder joing using a sufficiently powered iron for the gauge of cable otherwise you melt the insulation before the solder).

[Phil Addison]

I would only cut existing cable as a last resort. Can't you open up the hole a bit to get some clearance between cable and pipe? Or jam some cut-down plastic trunking in there to give protection from chaffing?

Phil The uk.d-i-y FAQ is at

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[raden]

In message , "Dave Plowman (News)" writes

NOT CPC again, 'fraid so ...

They sell a nice little catalytic heat gun with a shield which curves around the back of the wire. It runs on a cigarette lighter and costs around a tenner. It's not overly powerful, which can be an asset when using heatshrink.

[The Natural Philosopher]

No arguments there. Actually on solid copper I tend to for a U in each one to be soldered, and twist em up tight to completely lock together, then flow solder in to completely lock.

Crimps CAN be very good, and have one huge advantage over soldering - they do not stiffen stranded wire as solder runs up inside the insulation. This makes them very very good for areas of vibration, where solder joints would need to be (expensively) supported.

However the average house suffers little from vibration, and uses solid core wire anyway.

And, a crimp is totally dependent on how well its made. Its a bit harder to make a complete mess of solder as long as the iron is hot...

[Pete C]

Hi,

If you partly cover the intake on a hairdryer it should be hot enough to do the heatshrink - or possibly even catch fire!

cheers, Pete.

[Peter Parry]

Would that be why soldering is banned for Milspec, Naval and aerospace but crimps approved?

In terms of reliability it really is no contest - and solder isn't the winner - no matter how highly trained the gibbon.

[Dave Plowman (News)]

Since I bought the correct crimp tool - mega bucks - I'd not agree. The problem with soldered terminals in a car is that they are likely to fracture - they're not really designed for soldering, and the cable clamp is too close to the soldered part.

[Dave Plowman (News)]

Using the normal crimps and the correct tool it's a bit difficult to get it wrong...

Then just about every factory manages it - given the number of solder faults you get on older electronic equipment. Including those not subject to excessive heat and vibration.

[chris French]

And so is a solder joint.

You've not seen my soldering. It's pretty hard to make a mess of a crimp joint as long as you use the right tool, right crimp etc. I'ts much easier for me to make a dodgy soldered joint.

[The Natural Philosopher]

Thermal cycling. I forgot thermal cycling. Nasty on solder joints especially if they are under tensin from a crop-and-bend machine.

If crimps are so darned good, why don;t we have crimpable chips resitsiors, capaitors abnd circuit borads?

A good crimp is good on electrcal conductvity, on vibration resistance and on thermal cycling.

But it can fail like anything else. on stranded wire its potentally more subject to corrosion as well, as moisture can get trapped in the strands..

Wiring looms in aircaftt are not subject to the same set of conditions as mains wires in walls, and are totally dissimilar from mass produced crcuit boards in consumer equipment.

And trained aircfart technicians using proper equipment and subject to rigourous testing are not the same as half trained gibbons squeezing crimps with pliers and shoving them in a wall to be plstered over.

[The Natural Philosopher]

*shrug*. I do both. Crimps are bulkier and you have to have exactly the right crimp,and the right tool. Other wise they fall to pieces.