Woodshop Wednesday: Wiring an Electrical Box

Folks who normally plunge into DIY projects with reckless abandon are often scared to even touch the electrical system. And with good reason: electricity is dangerous. But the underlying concept of completing a circuit is actually pretty simple, and a good starter project for the faint-of-heart is to connect the wires inside an electrical box.

So, let’s focus on just the box and ignore where the cables go when they leave. This is a typical starting point: two cable ends inside the box, a fist’s length of each. Ready? Go!

Starting point: two big cables and a bunch of connectors.

Starting point: two big cables and a bunch of connectors.

Step 1: Strip the insulation. Get a utility knife deep in the box to score the insulation on both cables, then slide it off. You’ll reveal either three wires or four depending on the type of cable. In this case there are three. One wire is always coated black, one is coated white, and one is bare copper or sometimes green. Don’t worry just yet what the colors mean.

Step 1 in progress.

Step 1 in progress.

Step 2: Strip the ends of the conductors. Use a wire stripping tool to match the gauge of the wires. Clamp down on each of the coated wires a quarter inch from the end, and pull to expose the bare copper. The bare parts of the wire are what you’ll connect to complete the circuit.

Step 2 in progress.

Step 2 in progress.

Step 3: Connect like wires. That is, connect all the black wire in one juncture, all the white wires in another, and all the green/bare wires in a third. By convention, current flows in through the black “hot” wire, then travels through the fixture (in this case a light), then flows out through the white “neutral” wire. Despite the confusing names, current flows through BOTH the “hot” and “neutral” wires when the light is on, and it flows through neither wire when the light is off. The bare ones are grounding wires, which provide an escape path in the event of a short circuit but otherwise don’t carry a current.

Step 3 in progress.

Step 3 in progress.

Step 4: Fold all the wires neatly into the box and close the lid. Move on to the next box, where you can start over at Step 1.

Step 4 complete, minus the lid. This whole process is called "making up" an electrical box.

Step 4 complete, minus the lid. This whole process is called “making up” an electrical box.

This particular light fixture came with convenient snap-in junctures, with its hot, neutral, and grounding wires already attached. Outlets, switches, and many other lights come with just the wires, so you’ll have to provide your own snap-in or twist connectors. If you’re not confident about how to connect the wires, please consult a professional.

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