Occupancy sensor wiring diagram

Light: on

Move the space between occupied and vacant. A real sensor adds a time delay so a still person does not get left in the dark — the switching itself is this simple. The copper highlight is the live path, not a wire colour.

An occupancy sensor is a switch the room operates: it closes when it detects a person and opens again after the space has been empty for a set time. Wired in the hot to a fixture, it turns the light on when you walk in and off a while after you leave. Move the diagram between occupied and vacant to see it work.

Trace it yourself

Find the supply on the left. Upper terminal hot, lower terminal neutral. Finger on the hot.
Follow it into the sensor's first terminal. The space is occupied, so the blade lies on the second terminal. Go through.
Up and across on the switched hot to the top of the light. Cross the lamp.
From the lamp's bottom terminal, back along the neutral to the supply. Loop closed. Light on.
Now the space goes vacant. Nothing happens for a while — that is the hold-off timer — and then the blade lifts. Your finger stops at the sensor's first terminal, which is still copper. Light off, sensor live.

How this circuit works

Like the photocell, this is a single switch in the hot line — the shape of a plain single-pole. The difference is the trigger. Presence closes the contact and the hot reaches the lamp. Absence, once the hold-off timer expires, opens it again. The timer is the only thing between it and an ordinary switch, and it matters more than it looks: without it the light would flick off the moment you held still.

Whether it turns on by itself (occupancy) or only off by itself (vacancy) is a setting on the same device, not a different circuit. Both leave the switching topology exactly as shown here.

What goes wrong

1. Line and load swapped on the sensor

Symptom: the sensor is dead, or the lamp glows faintly and never fully switches.

A real sensor is not a bare blade — it has electronics behind the lens, and they draw their supply from the terminal marked line. Land the hot on the load terminal instead and the electronics are now fed through the lamp: the only way current can reach them is by trickling across the fixture first. On a filament lamp that trickle is a faint glow; on an LED driver it can be a flicker, or nothing. The switching part is drawn correctly and still cannot work, because the part that decides to switch has no proper supply. Line in, load out — same discipline as the GFCI.

2. The lens can see the corridor

Symptom: the light is on all day and nobody is in the room.

Nothing is miswired. Every time somebody walks past the open door, the lens sees a body, the blade closes, and the hold-off timer starts again from zero. In a busy corridor the timer never gets to the end. Read the diagram: the room's occupancy is just a switch, and the switch is being pressed by traffic outside the room. The fix is aim and placement, not wire.

3. The hold-off set too short

Symptom: the light drops out on someone sitting still, and they have to wave at it.

The sensor sees movement, not people. Sit still long enough and, to the lens, the room is empty: the timer runs out and the blade opens. A longer hold-off is the usual answer; where that is not enough, a sensor that also listens or one aimed to catch small motion at the desk. Worth knowing before you get called back to a "faulty" sensor that is doing exactly what the drawing says.

Sur le chantier

Almost nothing that gets a sensor called faulty is a wiring fault. It is the device fed through the load instead of from the line, it is the lens aimed at a doorway, or it is a hold-off time set for somebody else's room. Ten minutes of commissioning saves the return trip.

Common mistakes

Line and load swapped. The electronics end up fed through the lamp: a faint glow on a filament, a flicker or nothing on an LED driver, and a sensor that never properly switches.
The wrong device for the load. A sensor with no neutral takes its own supply as a trickle through the load. On modern drivers that trickle is a ghost glow or a stutter. Match the device to the kind of load, and give it a neutral where it wants one.
Aimed at the door. Every person who walks past the opening restarts the hold-off, and in a busy corridor it never reaches the end. Nothing is miswired; the lens is looking at the wrong room.
A wall-box sensor behind the door swing or a coat hook. The lens has to see the space, not the back of a jacket.
Leaving the hold-off at whatever the box shipped with. The sensor sees movement, not people; a desk worker sitting still is an empty room to it.
Calling a vacancy sensor faulty because it does not turn on by itself. That is the setting doing exactly what it says.

What the inspector looks for

The switching in the ungrounded conductor.
A neutral present at the box where the device needs one, landed and not just curled up behind.
The bond to the device and to the box.
Box fill, with the sensor's own body counted — they are deeper than a switch.
That the space has the automatic control the specification or the book asks for, and that it behaves the way the drawing says.

Check it before you call it done

Prove dead at the box.
Land line to the line terminal, load to the load terminal, plus the neutral and the bond. If the device has no markings you trust, the sheet in the box has them.
Energise and walk in. An occupancy setting comes on by itself; a vacancy setting waits for the press. Know which one you fitted before you decide it is wrong.
Sit still and time the hold-off with a watch. Set it for what this room does, not for what the box was set to.
Stand outside the doorway and walk past a few times. If the light comes on, mask the lens or re-aim before the cover goes back.
Put the plate on and check it is not shadowing the lens. A plate that crops the view turns a good sensor into an intermittent one.

Questions fréquentes

How does an occupancy sensor switch the light?

It detects a person — usually by their movement or body heat — and closes a switching contact to bring the light on. When it stops detecting anyone, a timer runs down and then it opens the contact and the light goes off. Electrically it is just a switch that the room operates.

What is the difference between occupancy and vacancy sensing?

An occupancy sensor turns the light on automatically when someone arrives and off when they leave. A vacancy sensor only does the off half — you switch it on by hand, and it turns off for you once the space empties. Same detector, different rule about the on part.

Why does the light stay on when I sit still?

The hold-off timer. A motion-based sensor can lose you if you stop moving, so it waits a set time after the last detection before switching off. That delay is why a still person is not suddenly left in the dark — and why the light lingers a while after you leave.

Voir aussi

Photocell wiring — switched by daylight instead of movement.
Single-pole switch wiring — the same circuit with a hand switch.
All wiring diagrams

Vous voyez une erreur sur cette page? Signalez-la

Merci — votre signalement a été envoyé.

L’envoi n’a pas fonctionné. Veuillez réessayer plus tard.