Power at Work: For a better wiring job, use heat shrink tubing

Monday, March 31, 2008

It's better than electrical tape, doesn't unravel and lasts far longer

by KEITH BERGLIND

Heat shrink tubing is a simple product often overlooked for sealing electrical connections. This easy-to-install product does a better job than electrical tape and it lasts far longer than a few wraps of tape.

Electrical tape is always my second choice for covering any electrical connections. I plan most jobs to be finished and sealed with heat shrink tubing.

This means putting the tubing looseon the wire before doing the soldering, and before clamping or crimping any connection.

Heat shrink tubing is a simple-looking plastic sleeve, which shrinks as soon as it is heated to over 70 C. Most brands of tubing will shrink to about half their size when heated by a heat gun or flame. Typically a quarter-inch tube can shrink down to one-eighth of an inch. In practice, the tubing is only heated until it shrinks tight. The tubing is only heated until you are satisfied with the look of the tight fit.

I normally use a heat gun for my jobs, mainly because I happen to have a quick-heat gun designed for welding plastic. Hair driers are not usually hot enough for this job. I also use a propane torch, but more care is required with that. I have seen mechanics using cigarette lighters and matches. Anything works, just do not overheat with an open flame, or the joint will look sloppy and distorted.

To start, I keep a supply of shrink tubing in the shop - a wide range of inside diameters of tubing, from one eighth to five eighths of an inch, and in short four-inch lengths, up to three-foot lengths. These products are available in electrical supply shops, such as The Source, Canadian Tire, Home Depot, etc. The long pieces are usually found only in specialty electronic supply stores.

I always prefer to solder all electrical connections, rather than use crimp-on connectors. The one problem to watch for is dealing with the heat from the soldering. It will cause the tubing to shrink before you can slip it over the new connection. So be sure to keep the tubing back from the soldered joint until the joint has cooled.

To start the job, slip a piece of tubing onto the wire, back from the soldering heat. Make the connection, then slip the tubing up in place and heat it until it shrinks neatly around your connection.

Special jobs. All too often, we manage to damage our favourite shop extension cords. Usually, this calls for some electrical tape, applied neatly.

But, will it last, and is it waterproof?

No, of course not. And in time the tape starts to unwrap and look sloppy.

Whenever I cut the outer layer of an extension cord, I remove one of the cord ends and slip on a short piece of heat shrink tubing. In Figure 1, note the double bulge on one of the three repairs, which was created when I put a short piece of tubing over a cut, heated it, and then put a longer piece of tubing over the top. It's over-kill of course, but it is my best 14-2 extension cord.

In cases where the inner insulation around one of the wires is also cut, I will cut this wire and peel back about two inches of the outer insulation, on one side, to hold the first tubing. After I re-connect the wire, the small tubing goes over the wire repair. Then a larger piece of tubing covers the whole wound.

Waterproof tubing. Common shrink tubing is waterproof enough for vehicles and shop use, but there are true waterproof tubing kits available.

The most common kits we use are for connecting wires to a submersible well pump. There is an inner layer of sealant which you will see squishing out at the end, as the tubing is heated, and which shrinks tight around the wire.

Wire ends and connectors. Since I always solder all wires ends, instead of crimping, I first have to cut off the plastic sleeve you find on most wire ends. Then, after making a solid soldered connection, I slip on a piece of heat shrink tubing. Neat and secure.

Heat shrink tubing also works great on pliers and other small handles. BF

Keith Berglind is a licensed heavy-duty mechanic.