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Les dispositifs de câblage courants

Every device in a box is marked by its maker so you can tell what it is and which terminal does what — brass for the hot side, silver for the neutral side, green for the bond, and a count of screws that names the device. Those are device conventions, the same across brands, and you can read them straight off the thing in your hand. Which conductor colour lands on which screw is a code rule, and it stays in your book — this page never names one.

Front views, drawn plain. Copper marks the terminals on the hot side where the drawing shows them.

  • ONOFF
    Single-pole switchTwo terminal screws on the hot side, and a handle marked ON and OFF. The bond screw is on the strap, behind this face.
  • 3-way switchThree screws — one darker common, two travellers — and no ON/OFF on the handle.
  • 4-way switchFour traveller screws, two pairs. Sits between two 3-ways; no common.
  • DimmerA slide or knob instead of a toggle, usually with leads instead of screws.
  • Duplex receptacleTwo outlets, brass side and silver side, with the break-off tab drawn joining each pair.
  • GFCI receptacleTest and reset buttons on the face; LINE and LOAD marked on the back.
  • Switch + receptacle comboOne yoke, two devices — often with a tab so the switch can control the outlet.
  • 240 V receptacleTwo hot slots and a U-shaped ground on a straight 240 V device; range and dryer outlets add a neutral. The slot pattern says which.

Two marks you will see moulded into receptacle faces: TR, tamper-resistant, has shutters behind the slots that only open when both blades of a plug push together, so a child cannot poke one slot; and WR, weather-resistant, is built to live in a damp or wet location cover. Where each is required is a code question. What the mark means is on the face.

The screws tell you the job

Pick up a duplex receptacle. Down one side are two brass screws, joined by a small metal tab; down the other side two silver screws, joined by a tab of their own; on one end a green screw bonded to the yoke. The brass side is for the hot, the silver for the neutral, the green for the bonding conductor. The tabs are what make both outlets one circuit — and the tab on the brass side is what you break off to make a split receptacle, with the top half on one circuit or a switch and the bottom always live. The duplex page lets you watch it happen.

A GFCI adds a second layer of marking. Its four terminals are in two pairs, LINE and LOAD, usually with a piece of tape over the load pair from the factory. Line takes the supply. Load feeds onward to receptacles you want protected by this device. Reverse them and the device's own face is not protected, and it generally will not reset — the GFCI page has the swapped version you can press the fault on.

A straight 240 V receptacle — the kind that feeds a heater, a compressor or a welder — has two brass terminals and a green: two hots and a bond, no neutral, no silver. Do not carry that over to every device marked 240 V. Range and dryer outlets are 125/250 V four-wire devices: two hots, a neutral on a silver terminal and a bond, because the appliance runs its clock, light and controls at 120 V off that neutral. Count the terminals before you assume. The slots are a different shape and spacing so a 120 V plug cannot enter, and that shape is the whole safety system: the configuration on the face says what voltage and current the receptacle is made for — and how many wires it wants.

Side-wire, back-wire, back-stab

Three ways a conductor can meet a device, and they are not equal. Side-wire is the hook of bare conductor under the screw head, wrapped clockwise so tightening the screw pulls it in — the connection every journeyman trusts. Back-wire (clamp terminal) puts the straight conductor into a hole in the back, and the side screw tightens a plate onto it; it is a screw connection with a straight wire, and it is fine. Back-stab is the plain push-in hole with a spring behind it and no screw. It holds by the edge of a spring on a small patch of copper, it loosens with heat and with the device being pushed into the box, and it is the connection behind a great many warm, flickering receptacles. Most crews simply do not use it. Know which hole you are looking at before you push a wire into it.

Whatever the method, the habit is the same: strip to the gauge on the back of the device, no insulation under the screw, no bare copper past it, and a firm tug on each conductor before the device goes into the box.

Which one is in this box?

You will open a lot of boxes with the packet long gone. Read the device:

  • Two brass screws, ON/OFF on the handle — single-pole switch. The simplest circuit.
  • Three screws, one darker, no ON/OFF — 3-way. The dark one is the common; the two matching ones are the travellers. The 3-way page shows why the common is the one that matters.
  • Four screws in two pairs, no ON/OFF — 4-way. It goes between two 3-ways and swaps the travellers; see the 4-way page.
  • Two brass, two silver, tabs between each pair — duplex receptacle. A broken brass tab means somebody made it a split.
  • Test and reset buttons — GFCI. Look for LINE and LOAD on the back.
  • Leads instead of screws, a slider or knob — dimmer. Its rating and the lamp types it is made for are on the label.
  • Two brass, a green, odd-shaped slots — a 240 V receptacle. The slot pattern is its rating.

Sur le chantier

Common mistakes

  • A traveller on the common screw of a 3-way — the light works from one switch only.
  • Supply landed on the GFCI's LOAD terminals; the device will not reset.
  • Conductor hooked counter-clockwise under a screw, so tightening pushes it out.
  • Back-stabbed connections on a circuit that feeds anything that draws real current.
  • Insulation under the screw, or a long bare tail touching the box.
  • The brass tab left intact on what was meant to be a split receptacle — both halves always live.
  • A device pushed into a box with the conductors folded so tight the terminals are strained.

What the inspector looks for

  • Conductors on the terminals the device marks for them, and the bond on the green screw or the yoke as the device is made for.
  • The right conductor identification on each terminal — the colour rules are in the book, and the inspector knows them.
  • Clockwise hooks, tight screws, no insulation trapped, no excess bare copper.
  • TR and WR marks where the location calls for them.
  • GFCI LINE and LOAD the right way round, tested with the button after power-up.
  • Devices that sit square and flush, not floating on their screws.

How to check a device dead, then live

  1. Breaker off, and locked if hands are going in.
  2. Meter proved live on a known source; every terminal to every other and to the box read; meter proved again.
  3. Wire it, tug each conductor, fold it into the box, fasten the device square.
  4. Power on. Read hot to neutral, hot to ground, neutral to ground at the face; on a GFCI, press TEST and confirm it trips and RESET brings it back.
  5. Work the switch and watch the load it controls, every position.

Questions fréquentes

How do I tell a 3-way switch from a single-pole in the box?

Count the screws and look at the handle. A single-pole has two brass terminal screws (plus the green bond screw) and ON/OFF printed on the toggle. A 3-way has three terminal screws — two the same colour for the travellers and one darker for the common — and the handle has no ON/OFF, because a 3-way has no fixed on position. A 4-way has four terminal screws in two pairs and no common.

Does brass always mean hot?

Brass is how the device manufacturer marks the side meant for the ungrounded conductor, silver the side for the grounded one, green the bond. That is a device convention you can rely on across brands. Which conductor colour goes to which screw is a code rule: the identification of conductors lives in your book, and this page deliberately does not name a colour.

What is wrong with the push-in holes on the back?

The plain push-in (back-stab) holds the conductor with a small spring against a flat contact. It is fast, and it is the connection most journeymen will not use, because it has less contact area than a screw and loosens with heat cycling and with a device that gets pushed around in the box. Back-wire clamp terminals are different: the conductor goes into a hole but a screw tightens a plate onto it. Those are fine. Learn to tell the two apart.

What do LINE and LOAD mean on a GFCI?

LINE is the pair of terminals the supply lands on. LOAD is the pair that feeds downstream receptacles so they are protected too. Get them backwards and the GFCI's own face is unprotected and the device usually will not reset. The interactive GFCI page on this site lets you press the fault with the terminals swapped and see exactly why.

Voir aussi

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