Heat shrink protecting T junction cable joins

How to insulate wire T solder joints with heat shrink tubbing. You can’t just slide heat shrink tubing over a T joint.

Heat shrink wire wrap is shrinkable plastic tube used to insulate stranded and solid wire joins and terminals. The tubing slides over exposed conductor wire, a little heat is applied and tubing shrinks to seal and protect it.

Where you have lots of wires in small spaces, such under baseboards or within a model, it’s invaluable to prevent exposed conductor wire touching and shorting out or causing other problems.

After a post on soldering in which I showed a technique for reliable solder joints including t-joins, where one wire joins another in the middle, a few readers contacted me to ask how I get heat shrink tubing to wrap around these three point joints.

In an end-to-end joint, the tubing can just slide over the join from one side of the wire but for T splices the leg of the wire will obviously prevent the tubing sliding across. A T-splice join, before soldering, on my layout is shown below, you can see how the outer tubing wouldn’t slide across this.

T-splice wiring join

I mentioned how I solved this problem in a comment to the article and said I’d follow it up with some more information. This is that follow up, how I wrap T shaped wire joins with heat shrink tubing. There maybe other solutions, and I don’t claim this is the best approach, but it works for me.

Firstly, I cut two short pieces of the tubing, one fits on the length of the cable that I’m cutting into – the top of the T –  and one wraps around the leg that will merge into it. (In the above photo you can just about see the tubing on the leg in the bottom left hand corner)

The first piece has a slit cut half way along from one end so it can slip over not both the main length of cable but also around the exposed conductor of the leg wire.  Once in place, I heat this to keep it in place.

The second piece, in the bottom left of the photo above, is slit part of the way along its length on opposite sides creating a skirt that flaps over the the other tubing when it meets it.

You can just about make out how the tubing is slit on either side with the two halves flapping out to wrap over the first piece of tubing in the next photo.

t junction wiring heat shrink tube

The tricky part is to now heat along the seam of the slits on both pieces sufficiently to seal slits but not burn a hole in it or causing it to shrink away. I use the wire from a hot foam cutter or shaft of a soldering iron tip to do this.

Lastly, with the two sections of tubing in place and the slits sealed, a modest heat is applied to the entire assembly to shrink it tight around the join, a match is my typical aid for this.

Heat shrink tubing

And that’s it.

It’s fiddly I accept and applying just the right amount of heat along the slits to weld them together takes some practice but the finished item prevents damage to the t-join or any shorts occurring.

A final, personal, note: I spend a huge amount of time testing, photographing, writing and researching techniques for these articles and pay for all the running costs of MRE out of my own pocket. If you found this article useful you can support me by making a donation on my fund-raising page. Thanks and happy modelling, Andy.

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