Wire strippers and crimpers: matching the tool to the gauge

Wire work is one of the few areas of DIY where a bad job is genuinely dangerous rather than merely ugly. A loose crimp has resistance; resistance makes heat; heat in a connector behind a panel is how fires start. The tools are inexpensive and the technique is learnable in an afternoon.

Reading the gauge markings

American Wire Gauge runs backwards: the larger the number, the thinner the wire. 22 AWG is a signal wire; 12 AWG is a household circuit. Every stripper and crimper has its usable range stamped on the jaw or printed alongside each notch.

Common ranges you will meet:

• 10–12 AWG — household circuits, larger automotive feeds
• 14–16 AWG — lighting circuits, general automotive
• 18–20 AWG — accessories, low-current wiring
• 22–24 AWG — signal, data, small electronics

Using the 14 AWG notch on a 20 AWG wire leaves insulation attached. Using the 20 AWG notch on 14 AWG cuts strands. Both are wrong and both are avoided by looking at the numbers.

Stripping properly

1. Pick the notch that matches the conductor, not the outside diameter of the insulation.
2. Squeeze until the jaws stop, then rotate a few degrees to score right round.
3. Pull straight off. Twisting as you pull is what shears strands.
4. Count the strands. If the stripped end looks thinner than the wire, you cut some. Cut it back and start again — a wire with a third of its strands severed carries a third less current at that point and heats up there.
5. Strip the right length. Too short and the crimp grips insulation; too long and bare copper stands proud of the connector. The barrel length of the terminal is your guide.

Crimping, which is where people go wrong

A crimp is a cold weld. Done correctly, the barrel deforms around the strands hard enough that they become one piece of metal. Done with pliers, it is a pinch that will work loose.

• Use the colour-matched die. Insulated terminals are colour-coded — red 22–18 AWG, blue 16–14, yellow 12–10 — and crimpers have matching dies. Using the wrong die is the most common fault.
• Terminal orientation matters. The seam of the barrel should face the indenter, not away from it.
• Crimp the barrel, not the insulation grip, in the first squeeze; double-crimp terminals need both, in the right order.
• Go to the ratchet stop. A ratcheting crimper will not release until full compression is reached. That is the feature you are paying for; a non-ratcheting tool leaves you guessing.

The pull test

Every crimp gets tested. Hold the terminal, pull the wire firmly. It should not move at all. If it slides, or if the wire comes out entirely, cut it off and do it again — that joint would have failed in service, probably at the least convenient moment.

It takes three seconds and it is the difference between a professional job and a hopeful one.

Soldering versus crimping

A properly made crimp is more reliable than solder in anything that vibrates, which is why the automotive and aviation industries crimp. Solder wicks up the strands and creates a hard point where the wire flexes, and that point eventually snaps.

Crimp for anything mechanical or automotive. Solder for board-level electronics that will not move.

Heat shrink, and doing it in order

The universal mistake: making the joint, then reaching for the heat shrink. Slide the sleeve on first, well back from the heat, then crimp, then slide it over and shrink it. Adhesive-lined shrink is worth the extra for anything exposed to weather.

Tool choice at the counter

A combination tool that strips, cuts and crimps is fine for occasional work and a compromise at all three. If you do more than a few joints a month, a dedicated ratcheting crimper and a separate stripper will make better joints faster. Tell us what gauges you work with and we will show you which jaw covers them.

Ferrules for stranded wire in terminal blocks

One case that catches people out: stranded wire clamped directly into a screw terminal. The screw crushes the strands, some break, and over time the connection loosens and heats. The fix is a bootlace ferrule — a small metal sleeve crimped over the stripped end so the screw clamps a solid cylinder rather than loose strands.

Ferrules need their own crimper with a square or hexagonal die. It is a modest additional tool and it is the correct answer any time stranded wire meets a screw terminal, which is most of the time in control panels and light fittings.

Colour codes, and not trusting them blindly

In US residential wiring the convention is black or red for hot, white for neutral, green or bare for ground. Automotive wiring follows manufacturer-specific colours that have no convention at all. Older installations follow whatever was done at the time.

Test before you trust. A non-contact voltage tester costs very little and belongs in the same drawer as the strippers. Colour tells you what somebody intended; a tester tells you what is actually there.

Heat shrink sizing

Shrink tubing is sold by its pre-shrink diameter and a ratio — 2:1 or 3:1. Choose a size that slides over the connector easily before shrinking and that will contract below the diameter of the wire. Too large and it will not grip; too small and it will not go on over the terminal.

Adhesive-lined tubing costs a little more and seals properly, which matters on anything outdoors or under a vehicle. A heat gun gives a much more even result than a lighter, and a lighter frequently chars the tubing and the insulation beneath it.