How do wire strippers remove insulation?

1. A wire has two parts. In the middle is copper, a metal that electricity flows through easily. Around it is a plastic coat called insulation, which keeps the electricity inside.
2. To join a wire to a battery or a lamp, metal must touch metal. With the plastic still on the end, nothing flows. Bare the tip, and the bulb lights.
3. Wire strippers look like pliers with sharp blades. Each blade has a row of half-round notches. When the jaws close, the notches meet and make round holes of different sizes.
4. Lay the wire in the hole that matches its copper, then squeeze. The blades slice through the plastic all the way around, and stop just before they touch the copper.
5. Keep squeezing and pull the tool toward the end of the wire. The cut piece of plastic slides off like a tiny sleeve, and the bare copper is ready to connect.
6. If the hole is too small, the blades cut into the copper and weaken it. If it is too big, they never get through the plastic. Only the matching hole strips cleanly.

Tap each part of the tool and the wire. Watch what it does.

• Handles. Squeezing the handles closes the jaws. The long handles work as levers, so a gentle squeeze makes a strong bite at the blades.
• Pivot. The pivot is a pin that joins the two halves. They swing around it, just like a pair of scissors.
• Spring. A small spring pushes the handles apart. When you let go, the jaws open by themselves, ready for the next wire.
• Notches. Each blade has sharp half-round notches. When the jaws shut, two notches meet and make a round hole. The edge of the hole cuts the plastic.
• Size numbers. A number beside each hole tells you which wire size it fits. The wire's size is often printed on its plastic coat, so you can match them.
• Cutter. Near the pivot the blades are straight, like scissors. This part cuts right through a wire to make it the length you need.
• Insulation. Insulation is the plastic coat around the copper. Electricity cannot flow through it, so it keeps the current in the wire and away from fingers and other wires.
• Copper conductor. The copper in the middle carries the electricity. It may be one solid piece or many thin strands twisted together, which bend more easily.

Drag the wire to a hole, or tap a hole. Try one that is too small, one that fits and one that is too big. Watch the close-up.

Experiment: What happens if you use a hole that is smaller than the copper?

1. Tap the smallest hole and watch the close-up.
2. Now find the hole where only the plastic is cut.
3. Try the biggest hole too. What do the blades touch?

What we found: A hole smaller than the copper makes the blades cut into the metal, so strands are lost and the wire is weaker. A hole much bigger than the wire never cuts the plastic. The matching hole cuts all the plastic and none of the copper.

Turn on JavaScript to try it yourself.

Strip all four wires cleanly to light the lamps. Careful: a thick coat can hide thin copper. Match the copper, not the coat!

Electric wires are made of two very different materials. Copper lets electricity flow easily, so it is called a conductor. Plastic does not let electricity through, so it is called an insulator. The plastic coat keeps the electricity inside the wire.

At the ends, the copper has to touch another piece of metal, so a short piece of the plastic must come off. You could try with scissors, but it is very hard to cut the plastic without cutting some copper too.

Wire strippers solve this with shape. When the jaws close, each pair of notches makes a round hole. The hole is a tiny bit wider than the copper of one wire size. The blades can cut inward only as far as the edge of that hole, so they slice the plastic and stop.

A hole that is too small cuts some of the copper away. A thinner wire carries electricity less well and can break when it is bent. A hole that is too big never reaches through the plastic. Real wires can carry dangerous electricity, so stripping wires is a job for grown-ups, with the power switched off. Our straw wrapper comparison is not perfect: a wrapper is loose, but insulation has to be cut before it will slide.

Key words

Conductor

A material electricity flows through easily, like the copper inside a wire.

Insulation

The plastic coat that keeps electricity inside the wire.

Wire gauge

A number for how thick a wire's copper is. A bigger number means a thinner wire.

Strand

One of the many thin copper wires twisted together inside a flexible wire.

Nick

A small cut in the copper that makes the wire weaker.

Check your thinking

1. What should the blades cut when you strip a wire?

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   Only the plastic insulation. The copper has to stay whole so it can carry the electricity.

2. You pick a hole smaller than the copper. What happens?

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   The blades cut into the copper and weaken the wire. The blades close further than the copper is wide, so they cut some of it away.

3. A wire has a very thick plastic coat. Which hole should you choose?

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   The one that matches the copper inside. The hole must stop the blades at the copper, so it is the copper's size that counts.

4. A hole only 70 percent as wide as the conductor closes on a wire. About how much of the copper's cross-section is left?

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   About 49 percent. Area goes with the square of the diameter: 0.7 times 0.7 is 0.49.

5. Why must the end of a wire be bare copper before you connect it?

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   Electricity cannot flow through the plastic. Plastic is an insulator. Metal has to touch metal for electricity to flow.

6. What is the safe rule for real electric wires?

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   Only grown-ups, with the power switched off. Wires can carry dangerous electricity. Grown-ups switch the power off before they touch them.