Soldering cable query.

[Northbeach]

Having never done this before (I have around 1 - 2 cm of cable to play with here - crimping and chok block out of the running now - thanks for the suggestion breezer) I'm a little cautious as to how I can do this correctly. I've had a quick rummage through the search section and 'heatshrink' often comes up in the replies.
I have spare 3 core mains cable (5mm, grey...) I was merely going to join to each core. Had a practice run on old bits of cable, but I think I'm going to struggle pushing the tight sleeving back down over the join. Might it be possible to keep the original sleeves on and tape over the joins...I'm assuming that this is where heatshrink comes in? Would I also need thinner cable to wrap around the existing cores?
The cable is barely poking out of the wall so this is a right feisty job!
Hope someone can help.
Cheers.

 

[Northbeach]

Ok sorted this in my head at least.
I have flex core in order to wrap this around the existing cable.
I'm struggling with finding Heat Shrink Tape however - I've just got back from a trip around the local electrical/hardware/pumbing stores - you name it...half have heard of it (but don't stock it) the other half havent'.
Searched on maplins and they store Heat Shrink Tubing - looks like my only option - is this ok in light of the lack of tape...or could I get away with insulation tape?

This shortening of the cable has turned into a right old headache!
Apologies for labouring you all with these queries...but the missus isn't too happy with me at the moment

Cheers folks.

 

[ricicle]

What is it that you are soldering ie what is the cable supplying, what two cables are you joining, and what is the reason for not crimping/connector blocking?

++++++
I think perhaps Northbeach is referring to an earlier post;
possibly //www.diynot.com/forums/viewtopic.php?p=466986&highlight=#466986
in which case he should have used "reply" rather than starting a new one.
M R
++++++

 

[ricicle]

Yeah I've just read the original

 

[Northbeach]

Oops - sorry folks...i didn't have a reply for that one and figured I was going off track ever so slightly, hence starting a post dedicated to soldering.
I managed to get hold of some heat shrink tubing (not the tape) so I'll try my hand at that.

 

[ricicle]

Soldering correctly takes practise so be sure you are confident before applying it to an electrical circuit and when you have done it make sure you are happy with the joint before covering with the heatshrink.Do not allow the solder to 'wick' the cable ie not cover the stripped back part all the way down to the insulation otherwise this leaves the joint stiff and can possibly snap off.Leave a small gap between the bottom of the solder and the insulation.Good luck

 

[Northbeach]

Thanks for the tip ricicle.
I'll be binding flex core around the original cable core then lay a coat of solder around this - I'll then wrap on the heat shrink sleeve (although I may have to get the next size up of tubing looking at it now...).
Cheers.

 

[davelx]

Thanks for the tip ricicle.
I'll be binding flex core around the original cable core then lay a coat of solder around this - I'll then wrap on the heat shrink sleeve (although I may have to get the next size up of tubing looking at it now...).
Cheers.

Hopefully you will not be laying a coat of solder AROUND the joint. That is not how a soldered joint works! If you stop at that point you will have a dry joint.

You must heat the cable up to the solder melting point with the iron BEFORE applying solder DIRECTLY TO THE CABLE, so that it flow INTO the joint. You do not need to cover the joint so you cannot see the wrapping strands, what you want is sufficient solder to flow into all the gaps and between the two main conductors but still be able to see the external detail of the wires. Do not moce the joint whilst the solder is solidifying. It should be bright and shiny when cool. If it is grey/dull/crystalline it is a dry joint - you did not heat the work up enough.

NEVER load solder onto the iron and carry it to the joint - that is a recipe for dry joints.

 

[Northbeach]

Thanks Davelx...I'm glad you posted this before I started (google is somewhat lacking in soldering information surprisingly). The last time I soldered was during an electronics class at school many years ago.

You must heat the cable up to the solder melting point with the iron BEFORE applying solder DIRECTLY TO THE CABLE, so that it flow INTO the joint.

Quick question from this - the original core/s will be wrapped with the flex core/s - won't the thinner flex strands melt before the stronger original core is sufficiently heated?

what you want is sufficient solder to flow into all the gaps and between the two main conductors.

Are you classing the flex cores as a conductor...or is it a case of using stripped flex cable to bind two seperate mains/lighting cable cores?

Appreciate the advice. I'll give this a few test runs first off.
Thanks.

 

[davelx]

You are only heating the joint up to the melting point of solder - not copper!

Yes, use a strand from a stripped flex core to bind together the two conductors tightly. Solder provides a good electrical connection but is not mechanically strong - binding with the thinner wire provides the mechanical support .

If I have a moment tonight, I'll do one on my bench and take a few photo's

 

[Northbeach]

OK...it was probably a silly question! But those flex strands look so fragile!
Do I need to 'tin' the iron beforehand? Although reading such a tinning methodology it contradicts your 'never load solder onto the iron' point.
I'm going to give your advice a whirl now...I'd honestly be looking at dry joints now had you not posted - many thanks.

 

[Northbeach]

Yes, use a strand from a stripped flex core to bind together the two conductors tightly. Solder provides a good electrical connection but is not mechanically strong - binding with the thinner wire provides the mechanical support .

If I have a moment tonight, I'll do one on my bench and take a few photo's

** only saw your first line of post when I replied on my last post.
I was under the impression that the flex core would be used as the actual cable to the new light fitting and not merely using the strands to bond between the two...I'll let you know how I get on - thanks for the photo offer also...it really is a fine art isn't it?
Cheers.

 

[davelx]

Yes, the iron must be tinned - but that is a very thin coating - you melt solder onto the bit then wipe it off with a damp sponge - there is no "blob" of solder left on the bit.

I would actually use something a bit thicker than a core from the flex to secure the cores - I have reels of 0.5 mm tinned copper wire for this.

Does this help?

 

[Northbeach]

Cheers Davelx...I don't have any other wire to wrap around and the trouble I'm facing is that the cable from the wall is barely reachable - it's a tight job here!

 

[Northbeach]

That pic does help although I'd understood from what you had written the type of workflow required (though your pic has three cores rather than two).
Had a few practices and I think I'm getting there - little bit tricky placing the iron underneath the bound wires and it's take some time to heat up (bog standard iron I have). I may have to get hold of larger heat shrink tubing mind...I have 2.5mm which looks like it will barely go over the joint...it will be a tight squeeze, especially when it's heat shrinked.
Cheers.