Duplex receptacle wiring diagram

Light: on

Unplug the load and the lamp goes out — but the receptacle terminals stay live. That is why you meter an outlet before you trust it. The copper highlight is the live path, not a wire colour.

A duplex receptacle is two outlets in one body, fed by a hot on the brass side and a neutral on the silver side, with a tab joining each pair so both halves are powered together. A plugged-in load draws current across the two; unplug it and the terminals stay live.

Trace it yourself

Find the supply on the left. The upper terminal is the hot, the lower is the neutral. Finger on the hot.
Follow it to the hot-side bar of the receptacle. The bar is the brass tab: both outlets share it, so the whole bar is live. Nothing is switched here.
Something is plugged in, so the blade lies on the cord. Go up the cord's hot to the top of the load. Cross the load.
Down the cord's other conductor to the neutral-side bar — the silver tab, also shared — and along the neutral back to the supply. Loop closed. Load runs.
Unplug it. The blade lifts. Your finger stops at the brass bar, which is still copper. Nothing is running, and both bars are exactly as live as they were. That is the outlet's normal state, and the reason you meter before you trust.

How this circuit works

The hot lands on a brass screw and, through the intact brass tab, powers both brass terminals. The neutral does the same on the silver side. Any load plugged into either half now sits across a hot and a neutral, so current flows through it and it works. The receptacle does not care whether the load is there — its terminals are energized either way.

That last point is the safety habit worth forming early: an outlet with nothing in it is not a dead outlet. Toggle the load off in the diagram and the copper stays right on the terminals. Break the brass tab and the two halves come apart — which is the next diagram along.

What goes wrong

1. Hot and neutral swapped — reversed polarity

Symptom: everything plugged in works. A plug-in tester shows the wrong lights. An appliance that is "off" is still live inside.

Put the hot on the silver bar and the neutral on the brass in your head. Trace it: the load still sits across hot and neutral, so current still flows and the lamp still lights. Nothing about the loop cares which side is which. The trouble is the appliance's own switch. It is built into the lead that expects the hot — and that lead is now the neutral. Switch the appliance off and it opens the return, not the supply: the heating element, the motor windings, the lamp socket all sit at line voltage while the thing is "off". Same physics as putting a wall switch in the neutral, one step further downstream. Brass is hot, silver is neutral, and the tester is how you prove it.

2. A loose joint on the feed-through

Symptom: every outlet beyond this one is dead, or flickers — and this one is warm.

Most receptacles feed the next one along, in and out of the same box. Add that to the drawing: a second hot leaving the brass bar to the next outlet. Now make the joint on the brass screw loose. Two things follow from physics. If the joint is open, the next outlet's hot is gone — everything downstream is dead while this outlet, fed from the supply side of the joint, works fine. If the joint is merely poor, it is a resistance in series with every downstream load, so it heats with all their current and the lights beyond it flicker as it moves. A dead run that starts at a working outlet is telling you where the bad joint is.

Sur le chantier

You will install more of these than anything else, and almost every one that comes back does so for one of two reasons: it is landed on the wrong side, or a joint is loose. Both are caught in the five minutes before the cover goes on.

Common mistakes

Hot on the silver side. The device marks itself — brass is the hot side, silver the neutral, green the bond. That is the device's own marking, not a wire-colour rule, and it is true no matter what the insulation looks like.
Back-stabbing a device that also has screws. A screw clamps the conductor across its whole width; a stab holds it with a leaf spring. The spring is the first thing to relax under a heater or a vacuum, and a relaxed spring is a hot joint.
Using the device as a splice. If the run continues through the tab, pulling the device kills everything downstream. Pigtail the feed-through so the circuit stands up with the device out of the box.
Wrapping the conductor anticlockwise under a screw so tightening pushes it out instead of pulling it in.
Not leaving enough conductor in the box to make the joint a second time. The next person to touch it has no material to work with.
Pushing the device home on the conductors instead of folding them behind it. That is how insulation ends up under a screw head.

What the inspector looks for

The bond: landed on the device, and to the box as well where the box is metal. The book says when the mounting screws alone are not the bonding path.
Box fill. The book gives the count and the allowance per item; you do the arithmetic for the box you actually used.
Conductor damage under the screw, and insulation caught under the clamp.
The device sitting square and flush, the cover closing without strain, and the box properly supported.
The arrangement the book wants for that location. A kitchen, a bathroom and an outdoor wall are three different places in the book, even though the device is the same.

Check it before you call it done

Breaker off. Live-dead-live at the box — prove your tester on a known live source both before and after.
Look at each joint before it goes in: a full wrap in the direction the screw tightens, or the clamp the device is built for, and no strands standing out.
Energise and put a plug-in tester in both halves of the outlet. Both must read the same and both must read correct.
Read hot to neutral and hot to bond: those two should agree. Neutral to bond should be nothing. If hot to bond is low and hot to neutral is right, the bond is not home.
Plug a real load in, leave it a few minutes, then touch the plate. Warm is a joint, not a load.

Questions fréquentes

Why does a receptacle have two brass and two silver screws?

Because a duplex is two outlets in one body. The brass screws are the hot side, the silver screws the neutral side, and a factory tab links each pair so both outlets are fed from one set of conductors. Feed one screw and the tab carries power to its twin.

What are the tabs for?

They join the two halves so a single hot and a single neutral power both outlets. Leave them intact for an ordinary always-on duplex. Snap the brass tab and you can feed each half separately — that is a split receptacle.

Is the outlet live even with nothing plugged in?

Yes. The terminals are energized whenever the circuit is on, whether or not anything is plugged in — unplug the load in the diagram and the receptacle stays copper. A plug simply completes a path through whatever you connect. Always meter before you trust an outlet dead.

Voir aussi

Split receptacle wiring — the same outlet with the brass tab broken.
GFCI wiring diagram — protecting a string of these downstream.
All wiring diagrams

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