Joining Wire with Solder and Heat Shrink

I’ve been having one of those weeks when you pick up a job and have to put it right back down again, as life throws you another curve ball.  But not wanting to drop the bat in this weeks post, I will be making it nice and short and answering another question I’m often asked at shows and exhibitions.  What’s the best way to join wires together?

This question is normally asked in regards to fitting a DCC decoder into a non-DCC ready locomotive.  This is called hard wiring and normally requires connection of all the DCC decoder’s wires directly to the locomotive.  Often there are wires already in the locomotive that can be utilized and connected to.  And, as is often the case, there is very little room spare to make a connection.  The smallest, and best, method of joining the wires is to solder them together but this causes a problem.  At the point where the wires are soldered they are exposed, and could come into contact with the locomotive body or other wires and cause a short, or worse damage the decoder.

The answer is to use heat shrink.  This is readily available at most hobby shops and electrical stores, and there is endless supplies on the internet.  Heat shrink is a rubbery plastic tube that when heated shrinks to encase whatever is inside.  To show how I join wires together I did a quick demo.

Below is a standard piece of multi core hook up wire and a piece of heat shrink that is just a bit bigger than the wire.

Wire Joint With Heat Shrink 1

Using a pair of wire strips I strip back a about 4 of 5mm of the insulation and using a pair of snips cut off a piece of heat shrink slightly longer, maybe 10mm.

Wire Joint With Heat Shrink 2

The heat shrink is then slid over one wire end.  Normally you would have two wires 🙂

Wire Joint With Heat Shrink 3

Then using the soldering iron I tin the ends of the wires.  This means flooding the end of the wire with solder.  Depending on how powerful your soldering iron is will determine how long this takes, but typically it’s only about one to two seconds.  Hold the iron tip to one side of the wire and apply some solder to the other, as the heat runs through the wire it will melt the solder, causing it to flood into the wire.  You don’t need to add much, just enough to cover the individual strands.

Wire Joint With Heat Shrink 4

Then place the two tinned ends together, its easer if one is attached to something as you need one hand to hold the iron.

Wire Joint With Heat Shrink 5

Simply touching the iron on the two tinned ends for one or two seconds will cause the solder to flow together making a solid joint. This will now be stronger that the wire and will give the best electrical performance.  Note: make sure the heat shrink is not right next to the joint when you do this other wise it might react to any heat traveling down the wire and shrink where it is.

Wire Joint With Heat Shrink 6

Then, once cooled for a few seconds, slide the heat shrink over the joint.

Wire Joint With Heat Shrink 7

The bump in the heat shrink is simply where one of the wire ends was sticking out a bit.  If the heat shrink wont slide over you can squeeze the joint with a pair of pliers just enough to flatten it out.  Then its time to activate the heat shrink.  Normally this is done with a special heat gun but I simply use the tip of the soldering iron or a cigaret lighter if there is one handy.  Which there wasnt tonight!  The flame from the lighter will ensure it shrinks evenly but the iron tip will do the job although it looks a little rougher.

Wire Joint With Heat Shrink 8

And that is how I join wires.

Hopefully things will get back to normal this week and I can get back on track.  I will be at the Fordingbridge Model Railway Exhibition this coming weekend so I will hopefully bring you a review of the show and layouts in next weeks post.