Hot, neutral, ground: the three wires

Light: on

Press the fault and watch the ground conductor go live for half a second — that is the path a fault takes home, and it is why the breaker opens. In a real circuit the breaker would clear it in a fraction of that time. Tap a conductor to replay its path. The copper highlight is the live path, not a wire colour.

Every circuit you will ever work on is these three jobs, over and over. One conductor brings the supply's pressure out to the load. One brings the current back. One sits idle, bonded to every piece of metal that could become live, waiting for the day something goes wrong. Learn the jobs and the circuits stop being pictures of wires and start being sentences.

Trace it yourself

Find the supply on the left. Two terminals: one is the hot, one is the neutral. The ground tie hangs off the neutral just below.
Follow the hot along the top to the lamp. Nothing interrupts it here — no switch yet. That is the pressure arriving.
Cross through the lamp. The lamp is the only place in this drawing where the hot side and the return side meet, and that is why it is the only thing that lights.
Follow the neutral back to the supply. The loop is closed. Current flows.
Now follow the ground from the tie, along the bottom, up to the metal box. Notice it never meets the lamp. It touches only the metal.
Press the fault. Watch the hot reach the box, and the ground path light up all the way home. That is a fault current, and it is what a breaker is for.

The hot: the pressure going out

The supply holds one of its terminals at a different potential from the ground you are standing on. That difference is the voltage, and the conductor that carries it out into the room is the hot. Follow it from the supply on the diagram: it runs straight to the lamp. On a lighting circuit it is the hot that gets switched, because opening the hot leaves the fixture with no pressure on it at all. Open the neutral instead and the light also goes out — but the fixture is still sitting at line voltage, waiting. That is why the single-pole switch breaks the hot and never the return.

The neutral: the return

Current is a loop or it is nothing. Whatever leaves the supply on the hot has to come back, and the neutral is the conductor it comes back on. It is held close to ground potential at the supply, which is why it feels tame on a meter — but while the lamp is on, the neutral is carrying exactly the same current as the hot. Tap the neutral on the diagram and watch the trace: it is the second half of the same path, not a spare wire. The trade word for it is the grounded conductor, which trips people up: it is grounded at the supply, and it is not the ground.

The ground: nothing, until it matters

The third conductor carries no current in a healthy circuit. Look at the diagram at rest: the hot glows, the neutral glows, and the ground sits grey. It runs from the supply — where it is tied to the neutral — out to the metal box around the lamp, and to every other piece of metal a person might touch. Its whole purpose is the moment a hot conductor comes loose and lands on that metal. Press Fault: hot touches the box and watch. The ground path goes live, current pours back to the supply along it, and in a real circuit the breaker sees that surge and opens in a fraction of a second. Without the ground, the box would simply sit at line voltage, tripping nothing, and the first person to touch it would become the return path instead.

Two words the trade uses here: bonding is tying the metal together so it is all at one potential and has that low-resistance path home; grounding is tying the system to the earth itself. They are different jobs that share a conductor, and the glossary page on bonding vs grounding takes the distinction further.

Why this page never says a colour

Which colour marks the hot, the neutral and the ground is a rule in the Canadian Electrical Code and its local amendments, and there are cases — a re-identified conductor, a switch loop, a 240 V circuit with no neutral at all — where the colour you expect is not the job the conductor is doing. Learn the job first. Then the colour rule in your book is a label on something you already understand, and a meter is what tells you the truth on the day.

What goes wrong

Three faults, one per wire. Each one is invisible at the light switch and obvious the moment you trace the drawing.

1. Open neutral

Symptom: the lamp is dark, the switch is on, and a meter finds voltage at the fixture.

Break the return in your head, anywhere between the lamp and the supply. The hot still arrives at the lamp — nothing stopped it — but the current has no way home, so nothing flows and the lamp is dark. The fixture is sitting at line voltage with no current in it. A dark lamp that reads live is a broken return, not a broken supply, and it is the reason "the light is off" never means "the fixture is dead".

2. Neutral and ground swapped at the box

Symptom: everything works. The ground conductor is warm, and so is every bonded box between here and the panel.

Land the lamp's return on the ground instead of the neutral. Trace it: hot to lamp, cross the lamp, and now the current goes home along the ground — through the metal box, along the bonding path, through every other box on the run, to the tie at the supply. The loop is closed, the lamp lights, nothing trips. But the conductor that was supposed to carry nothing until a fault is now carrying the lamp's full current all day, and every piece of metal it touches is part of a live circuit. Physics is perfectly happy with it. That is exactly the problem.

3. The ground left off

Symptom: nothing, for years. Then a fault, and the box is live and nothing trips.

Erase the ground from the drawing. Healthy circuit: no change at all — it carried nothing anyway. Now press the fault. The hot lands on the box, and there is no path from the box back to the supply, so no fault current flows and no breaker sees anything. The box simply sits at line voltage, waiting. The first person to touch it while standing on something that is grounded completes the circuit themselves. A missing ground is the one fault that gives no symptom until the day it gives the worst one.

What comes next

Now put a switch in the hot. The single-pole switch diagram is this exact circuit with one blade added, and you will already know why the blade is on the hot side. Then run the Ohm's law drill to put numbers on the pressure and the current you just traced. Both are the next steps on the start-here path.

En la obra

Three conductors, three jobs — and nearly every receptacle call-back is one of them doing the wrong job. Here is what that looks like in a box, what gets checked at the walk-through, and how you prove it before you put the cover on.

Common mistakes

Reversed polarity. Hot and neutral swapped at a device. The lamp still lights, so nobody notices — but the shell of every lamp holder downstream is now the hot, and the switch is breaking the return instead of the supply.
An open ground. The bonding conductor never landed, or landed on a screw that grips paint instead of metal. The circuit works perfectly right up to the day something faults onto the box.
Neutral touching ground downstream. A stray strand, a neutral landed on the bonding screw by habit. Nothing trips, but return current now has two roads home and the bond carries load current it was never meant to.
Trusting the colour. A conductor that looks like a neutral is not proven to be one until the meter says so — the switch-loop page shows a case where it is a hot.
A loose neutral. The hot gets all the attention; the neutral is the half of the loop that quietly overheats when its screw is not tight.

What the inspector looks for

The bond: every metal box, every device, tied back through a conductor that is actually landed, not resting in the box.
Polarity at the devices — hot on the brass screw, neutral on the silver, and a plug-in tester in a receptacle or two to confirm it.
Where neutral and ground are tied together. The book says there is one place for that connection; anywhere else is a finding.
That the conductors are identified the way the book says they must be — the colour rule is theirs, the inspector just checks you followed it.
Terminations: one conductor per screw unless the device is listed for more, and no insulation under the screw.

Check it before you call it done

Prove dead before you touch anything: meter on a known live source, then the circuit, then the live source again — the live-dead-live habit from meter safety.
With power off, continuity from the receptacle's bonding screw back to the panel bond. A reading of "open" here is the fault the tester cannot see.
Energise and read three voltages: hot to neutral (full supply), hot to ground (the same), neutral to ground (near nothing). A reading between neutral and ground that is not near zero means the return path has a problem.
Plug in a three-lamp tester and read the legend. It catches reversed polarity and an open ground. It cannot catch a bond made through a bad joint that still passes a trickle, and it cannot tell a real ground from a neutral-to-ground jumper at the device — that is why you did step 2.
Put the cover on only after the meter, not the lamp, has told you the three jobs are on the three conductors.

Preguntas frecuentes

Which wire is the hot?

The one that carries the supply voltage out to the load — the conductor that is at a different potential from the ground you are standing on. On a diagram it is the conductor that leaves the supply and reaches the switch or the load first. Which colour identifies it is a code rule, so look that up in your book, not here.

Does the neutral carry current?

Yes — in a working circuit the neutral carries every bit of current the hot does, because it is the return half of the same loop. That is why it is treated as a live conductor when the circuit is on, even though it sits near ground potential. "Near ground" and "safe to touch" are not the same claim.

What does the ground actually do?

Nothing, most of the time — and that is the point. It ties every piece of metal that could become energized back to the source through a deliberate low-resistance path. When a fault puts the hot on that metal, a large current flows down the ground path, the breaker sees it and opens. Press the fault button on the diagram and watch that path go live.

Why are the neutral and ground tied together at the supply?

So a fault has somewhere to go. If the ground path were not connected back to the source, a fault would put the metal at line voltage and nothing would flow — nothing would trip, and the box would sit there waiting for a hand. Where that one connection is made, and the rule that it is made only there, is code; the diagram shows only that it exists.

Ver también

Single-pole switch wiring — the same circuit with the hot switched.
Glossary: hot, neutral, ground and the other first-week words
How to read a schematic — if the drawing itself is new to you.
Meter safety and CAT ratings — the live-dead-live check, and why the meter's rating matters.

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