3-Wire Motion Sensor Light Wiring Diagram: How to Wire a PIR Sensor Light

3-Wire Motion Sensor Light Wiring Diagram: How to Wire a PIR Sensor Light — interactive diagram. Open it in the editor to customise components and wiring.

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A clear wiring reference for connecting a three-wire passive infrared (PIR) motion sensor light to a standard lighting circuit, including load switching, sensitivity adjustment, and timer settings.

A three-wire passive infrared (PIR) motion sensor light unit typically has three conductors exiting the sensor head or fitting: a permanent live (supply), a neutral, and a switched live output to the lamp. This wiring arrangement allows the sensor to power its internal electronics from the supply continuously, while the switched live output turns the lamp on and off based on detected motion and the sensor's set time delay.

Understanding the distinction between the permanent live and the switched live is the most important concept in PIR sensor wiring. The permanent live feeds the sensor's internal circuit at all times — even when the lamp is off — so the sensor remains active and ready to detect movement. The switched live output energises the lamp when motion is detected and de-energises it after the timer period expires.

Some PIR sensor fittings are supplied as complete luminaires (lamp and sensor combined), in which case the three terminals presented at the back of the fitting are simply the supply connections: permanent live, switched live return to the lamp circuit (or a permanently connected internal lamp), and neutral. Always consult the manufacturer's installation instruction sheet for the specific fitting before wiring.

Most PIR sensor lights include two or three adjustment controls, typically accessible through a small cover on the sensor head: a sensitivity (LUX) control that sets the ambient light level below which the sensor will trigger (preventing daytime activation), a time control that sets how long the lamp remains on after the last detected motion (typically adjustable from approximately 5 seconds to 30 minutes), and sometimes a distance control for detection range adjustment.

This page is a generic illustrative reference. All electrical installation work must comply with the applicable wiring standard (BS 7671, NEC/NFPA 70, AS/NZS 3000, IEC 60364, or local equivalent) and must be carried out by a qualified electrician where required by law.

How to wire 3 wire motion sensor light wiring diagram

Isolate the circuit and verify dead Switch off the circuit breaker supplying the lighting circuit at the consumer unit. Apply a lockout clip or personal lock if available. Use a non-contact voltage tester, then verify with a calibrated multimeter using the proved-live, prove-dead, proved-live sequence at the fitting location. Do not begin any wiring work until all conductors are confirmed dead.
Remove the existing fitting and identify cables Remove the existing lamp or fitting. Identify all conductors in the back box or ceiling rose. Photograph the existing wiring before removing any connections. In a standard loop-in lighting circuit, you will find a permanent live, neutral, and a switched live (switch wire). If this is a new installation, consult the manufacturer's wiring diagram and the applicable wiring standard for how to bring the supply to the fitting location.
Connect the PIR sensor fitting conductors Following the manufacturer's wiring diagram for the specific fitting: connect the permanent live (brown) to the fitting's supply/live terminal, the neutral (blue) to the fitting's neutral terminal, and the earth (green/yellow) to the earth terminal. The switched live output to the lamp is internal to the fitting in an all-in-one luminaire, or connects to the external lamp live terminal in a sensor-only unit. Tug-test all connections.
Fit the sensor and direct the detection arc Mount the fitting securely to the back box or surface mounting plate. Direct the PIR sensor head towards the area to be monitored. Note that PIR sensors typically have a detection arc of 90–180 degrees horizontally and a narrower vertical angle — consult the product data sheet for the detection pattern. Do not aim the sensor directly at a south-facing wall (in the northern hemisphere) that receives direct sunlight, as solar heating of the wall surface can trigger false detections.
Set the LUX and timer controls Locate the adjustment controls on the sensor head. Set the LUX control (ambient light threshold) to approximately mid-point initially. Set the timer control to the desired delay period (e.g., 1–2 minutes for a driveway or front door). Some sensors have a test/override mode activated by setting the timer to minimum — use this during commissioning for rapid testing without waiting for the full timer period.
Restore power and commission Restore the circuit breaker. The sensor will usually require a brief initialisation period (typically 30–60 seconds) before it begins detecting — during this time it may hold the output on or off depending on design. After initialisation, walk through the detection zone and verify the lamp activates. Shield the sensor from ambient light and verify the LUX control is not preventing nighttime operation. Adjust controls as needed.

Specifications

Sensor type	Passive Infrared (PIR) — detects change in infrared radiation emitted by moving warm bodies
Typical supply voltage	230 V AC, 50 Hz (or 120 V AC, 60 Hz for North American variants)
Typical switched load rating	300 W – 2000 W resistive (varies by product — check manufacturer label); LED rating may be lower
Detection angle (typical)	90–180 degrees horizontal; 15–30 degrees vertical — varies by product; verify in data sheet
Detection range (typical)	6–12 metres — varies by sensitivity setting and product design
Timer delay range (typical)	5 seconds to 30 minutes — adjustable via timer control on sensor head
LUX threshold range (typical)	3–2000 lux — adjustable via LUX control on sensor head
Minimum IP rating (outdoor)	IP44 (protected against splashing water); IP65 recommended for exposed outdoor locations

Safety warnings

ISOLATION MANDATORY: Switch off and verify the lighting circuit is dead before removing any existing fitting or making any connections. A lighting circuit that appears dead at the switch may still have a live feed present at the ceiling rose or back box. Verify with a calibrated multimeter.
QUALIFIED PERSONNEL: Electrical wiring installation must be carried out by a qualified electrician in accordance with the applicable wiring standard (BS 7671, NEC/NFPA 70, AS/NZS 3000, IEC 60364, or local equivalent). In many countries, domestic electrical work requires notification to building control or certification through a competent person scheme.
MAXIMUM LOAD RATING: Do not connect a lamp load that exceeds the PIR sensor's switched output rating. Overloading the sensor's internal relay or triac can cause it to overheat and fail — potentially as a fire hazard. Verify the lamp wattage (including LED inrush compatibility) against the sensor's label.
OUTDOOR INSTALLATIONS: External PIR sensor fittings must have an IP (Ingress Protection) rating appropriate for their location — typically IP44 or higher for wall-mounted outdoor fittings, IP65 for exposed or wet locations. An incorrectly rated fitting exposed to rain and moisture can become a shock and fire hazard.
EARTH CONNECTION: Connect the earth conductor to the fitting's earth terminal even if the fitting body is plastic. If any metal components are present (lamp holder, faceplate, mounting bracket), earth continuity is mandatory.

Tools needed

Calibrated non-contact voltage tester (NCV tester)
Calibrated digital multimeter (for voltage verification)
Flathead and Phillips insulated screwdrivers
Side cutters and wire strippers
Personal lockout device and danger tag
Drill and masonry bit (for surface mounting in masonry)
Socket tester (if a socket outlet is also being tested on the same circuit)

Common mistakes

Connecting the permanent live and switched live in reverse — the sensor draws its operating power from the switched output instead of a permanent supply, causing it to detect motion but switch off its own power supply, resulting in a rapid on-off cycling ('chattering') fault.
Exceeding the sensor's maximum switched load, particularly with LED drivers that have high capacitive inrush current — check the manufacturer's LED compatibility rating, not just the wattage rating.
Aiming the sensor at a heat source — air conditioning units, boiler flues, and sun-heated surfaces all emit infrared radiation that a PIR sensor cannot distinguish from a human body.
Fitting an indoor-rated PIR sensor in an outdoor or semi-exposed location — moisture ingress causes erratic operation, corrosion of the relay contacts, and potential shock hazard.
Not performing an earth continuity check — a lost earth connection on an external fitting creates a shock hazard that will not be apparent until a fault energises the metalwork.
Setting the LUX control too high during commissioning on a bright day — the sensor appears to work correctly in the workshop, but once installed in bright outdoor conditions, it refuses to activate at dusk because the LUX threshold is too low.

Troubleshooting

Light stays on continuously and does not switch off: Cause: Timer control set to maximum, LUX control set too high causing sensor to always detect 'dark', sensor aimed at constant heat source, or internal relay/triac fault Fix: Set timer control to minimum (test mode). Manually shade the sensor — if the light stays on regardless of movement or darkness, the switched output is permanently energised, indicating a sensor fault. If the light switches off when the sensor is shaded, adjust the LUX control to reduce ambient light sensitivity.
Light never activates on movement: Cause: No permanent live supply to sensor, LUX control preventing activation in ambient conditions, sensor detection arc not covering the target area, or lamp failure Fix: Verify permanent live and neutral are present and correctly connected at the sensor terminals. Test the lamp in a known-good socket. Set the LUX control to maximum (most sensitive). Walk slowly through the centre of the sensor's detection zone at the range recommended by the manufacturer.
Light flickers or activates erratically with no visible movement: Cause: False triggers from insects in front of sensor lens, nearby vehicle headlights sweeping the area, a heat source within the detection zone, or electrical interference on the supply Fix: Inspect the sensor lens for spider webs and insects. Reposition the sensor to avoid vehicle traffic arcs. Reduce the sensitivity control. If flicker occurs at a specific time, correlate with known heat or light sources. If electrical interference is suspected, fit a suppression capacitor across the supply (as recommended in the product installation sheet).
Circuit breaker trips when the PIR light activates: Cause: Lamp load (including LED inrush) exceeding circuit breaker rating, short circuit in wiring or lamp, or faulty sensor switched output short-circuiting to neutral Fix: Verify the total load on the lighting circuit does not exceed the MCB rating. Remove the lamp and measure insulation resistance between the switched live output and neutral. A very low reading indicates a fault in the sensor output circuit or wiring. Replace the sensor if the short circuit is confirmed within the sensor unit.

Frequently asked questions

Why does my PIR sensor light stay on all the time?

The most common cause is the LUX (sensitivity) control being set too high — the sensor triggers in daylight because it cannot 'see' that ambient light is sufficient. Turn the LUX control anticlockwise to reduce sensitivity. Also check that the sensor head is not aimed at an artificial heat source (boiler flue, air conditioning unit) that triggers it continuously.

Why does my motion sensor light not turn on at night?

Check the LUX control — if set too low, the sensor may decide it is too bright even at night (from streetlights or security lighting). Turn the LUX control clockwise. Also verify the sensor is correctly wired (permanent live and neutral present), the lamp is not blown, and the sensor's detection arc is aimed at the area to be covered.

Can I wire two PIR sensors to control one light?

Yes. Connect the switched live outputs of both PIR sensors to the live terminal of the lamp. The lamp will activate when either sensor detects motion. Both sensors require their own permanent live and neutral supply. This is a common arrangement for large areas or corner coverage.

What is the maximum load I can connect to a PIR sensor's switched output?

The maximum load (wattage or current) is stated on the sensor's label or installation sheet. Typical domestic PIR sensor switches are rated between 300 W and 2000 W for resistive loads (incandescent, halogen). LED loads are sometimes quoted separately and may be rated lower due to capacitive inrush — always check the label.

Do I need to earth a plastic-bodied PIR sensor light fitting?

If the fitting is entirely plastic (Class II, double-insulated), an earth connection may not be required by the standard. However, if the fitting has any accessible metal parts, or if the lamp holder or faceplate is metal, an earth connection is mandatory. If in doubt, connect the earth — it does not cause harm and provides an additional safety margin.

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