The wiring jobs worth doing yourself and the ones that aren't

Turn the breaker off. Then prove it's off with a tester, at the device you're about to touch, before your fingers go anywhere near a wire.

That's the whole job in one sentence. Everything else is screws and sequence.

Home wiring intimidates people more than it should, and then it catches out the people it doesn't intimidate enough. The middle ground is narrow and worth learning: there are three or four jobs almost any careful adult can do properly, and a clear line past which you call someone licensed. This is where that line sits, and how to do the work on your side of it.

What you need before you start

A non-contact voltage tester, the pen-shaped kind. A plug-in receptacle tester with three lights. A pair of wire strippers with numbered gauge holes. A #2 Phillips and a small flathead. Lineman's pliers. Wire connectors in the right sizes. Electrical tape. A headlamp, because the light in the room you're working on will be the light you just switched off.

Buy the two testers even if you buy nothing else. They cost less than a takeaway dinner and they're the difference between a routine job and a very bad afternoon.

One thing to check before you open anything: if your house has aluminum branch wiring, knob-and-tube, or cloth-insulated conductors, stop reading this as a to-do list. Those systems need a qualified electrician with the right connectors and methods. Aluminum in particular is not a "be careful" situation. It's a hands-off situation.

Killing the power properly

Find the breaker. If the panel labels are wrong — and in older houses they usually are — plug a lamp into the receptacle or leave the light on, then flip breakers until it dies.

Switch the breaker fully off, not to the tripped middle position. Put a piece of tape over it and write something on it, or at minimum tell everyone in the house what you're doing. People turn breakers back on to see what they do.

Now go back to the device. Touch the voltage tester to the wires, to the screw terminals, into the receptacle slots. Test the tester first on something you know is live, so you know the battery isn't flat. Then test the thing you're working on.

Two warnings. A switch box can contain wires from a second circuit that you haven't killed. And a receptacle can be fed from one breaker while a neighbouring device in the same box is fed from another. Test every conductor in the box, not just the ones you're planning to touch.

Only when nothing reads live do you start unscrewing.

Replacing a receptacle

Take a photo of the existing wiring before you disconnect anything. You'll want it in twenty minutes.

Unscrew the cover plate, then the two screws holding the device to the box. Pull the receptacle straight out. You should see a black wire on a brass screw, a white wire on a silver screw, and a bare or green wire on the green screw. Sometimes there are two sets, because the circuit continues to the next outlet.

If the old wires are jammed into the little holes in the back rather than wrapped around screws, that's a backstab connection. Cut them off and start fresh with screw terminals. Backstabs rely on a small spring clip, and they loosen over the years. A loose connection is what heats up.

Strip about three-quarters of an inch of insulation, using the correct numbered hole so you don't nick the copper. A nicked conductor is a weak conductor. Bend a hook in the end with your pliers, hook it around the screw clockwise so tightening the screw pulls the wire closed rather than pushing it out, and snug it down firmly. Firm, not gorilla-tight. You'll feel the screw bite.

Ground to green, white to silver, black to brass. Fold the wires back into the box in an accordion, not a tangle, push the device in square, and screw it down.

Switches and fixtures

A single-pole switch is the same job with less to remember: two hot conductors and a ground, and the two hots are interchangeable. Note which way is up before you pull it out.

A three-way switch — one of a pair controlling the same light from two places — is different. It has a common terminal, usually a darker screw, and two travellers. Label the wire on the common terminal with tape before you disconnect it. Get that one wrong and nothing works in a way that will take you an hour to unpick.

Light fixtures add weight and gravity. Support the old fixture before you undo the last screw. Check that the box in the ceiling is a fan-rated box if you're hanging anything heavy or anything that spins; a standard box isn't built for it. Connect like colours with wire connectors, twist until the connector is tight, then tug each wire to confirm it holds.

What goes wrong

Reversed polarity — hot on the silver screw — is the most common mistake, and a plug-in tester catches it in three seconds.

Over-stuffed boxes are the second. Every conductor, device and clamp takes up space, and the code has a calculation for it. If you're fighting to push things back in, you likely have a box that's too small for what's in it.

Then there's the gauge mismatch. A 15-amp breaker protects 14-gauge wire; 20 amps needs 12-gauge. If you ever find yourself thinking a bigger breaker would stop the tripping, understand what you're proposing: removing the protection from a wire that's telling you it's overloaded.

Where you stop

Inside the panel. All of it. Even with the main breaker off, the service conductors feeding the panel are still live, and there's no breaker in your house that turns those off.

Adding a new circuit. Moving a circuit. Anything that changes what's connected to the panel.

Anything outdoors, underground, in a crawlspace, or anywhere near water or a pool.

Anything involving a subpanel, a generator interlock, solar, or an electric vehicle charger.

Anything on a multi-wire branch circuit — two hots sharing a neutral, often two breakers tied together. Disconnecting the shared neutral while the circuit is energised can put a dangerous voltage where you don't expect it.

Any smell of burning, any scorch mark, any melted insulation, any breaker that trips repeatedly. That's a symptom, not a nuisance.

And this one, above the rest: anything you open up and don't understand. Five wires where you expected three, unfamiliar colours, a junction of connectors stuffed into a box with no cover. Put the plate back on, leave the breaker off, and make the call. There's no shame in it, and a licensed electrician charges far less to fix nothing than to fix a fire.

Check your local rules too. Plenty of jurisdictions let a homeowner do simple device replacement but require a permit and inspection for anything beyond it. Your insurer may have a view as well.

The last five minutes

Restore power. Plug in the three-light tester and read it against the legend on its side. Test the switch, test the fixture, test the other receptacles on the circuit in case you disturbed a shared connection.

Then take a pencil and correct the breaker label in the panel, because you now know something the last person didn't.

Do that on every job and in a few years you'll have a panel that tells the truth — which is a gift to whoever owns the house after you, including your own family at two in the morning with water coming through a ceiling.