Motion Sensor Light Wiring Diagram: PIR Switch Connection, Load Wiring & Override Modes
This is a free printable motion sensor light wiring diagram: download the diagram as SVG or open it and print to paper or PDF.
Understand how to wire a passive infrared (PIR) motion sensor to control a light fixture — covering switched live routing, load connection, override test mode, and common single-sensor and multi-sensor configurations.
A passive infrared (PIR) motion sensor detects the difference in infrared radiation between a moving warm body (a person, animal, or vehicle) and the ambient background. It does not emit radiation — it only receives. When it detects motion, it closes an internal relay or triac, energising the connected lighting load for a preset time period (the hold-off or time delay, typically adjustable from 10 seconds to 30 minutes).
From a wiring perspective, a PIR motion sensor is simply an automatically operated switch inserted into the switched-live conductor of the lighting circuit. The mains supply (live and neutral) must reach the sensor — the sensor needs a small continuous power supply for its electronics. From the sensor's switched output, the switched-live travels to the lamp. Neutral goes directly from the supply to the lamp without passing through the sensor.
This three-wire requirement (live in, neutral in, switched live out) is the key wiring difference between a PIR sensor and a simple manual switch. A standard 2-core switch drop cable (live and neutral) is sufficient. The sensor body typically has three clearly labelled terminals: L (live in), N (neutral in), and a symbol or label for the load/switched output (sometimes marked with a lamp symbol or 'LOAD').
In a retrofit installation replacing a manual switch with a PIR sensor, the original switch typically had only the live conductor passing through it. To wire a PIR sensor in the same location, neutral must also be available at that location — either by using a three-core cable or by running a new two-core cable from the nearest junction point where both live and neutral are accessible.
Most PIR sensors include adjustable sensitivity (detection range), time delay (how long the light stays on after the last detected motion), and a lux (daylight) sensor that prevents the sensor from switching the light on in daylight — useful for outdoor security lighting that should only operate after dark.
Override modes are a frequently misunderstood feature. Many sensors have a manual-on override: holding the sensor's test button or keeping the wall switch off-on-off in a specific sequence latches the light permanently on until manually switched back to auto mode. The test mode reduces the time-delay to 2–5 seconds to allow function testing without waiting the full time delay.
All wiring must comply with IEC 60364, BS 7671, NEC Article 410, AS/NZS 3000, or the applicable national standard.
How to wire motion sensor light wiring diagram
- Confirm that both live and neutral are available at the sensor mounting location Check whether the existing switch drop contains only live (2-core cable with just a switched live path) or both live and neutral (3-core, or a 2-core where neutral is also present). If only live is present at the switch location, run a new 2-core or 3-core cable from the ceiling rose or junction box to the sensor location before proceeding.
- Isolate the circuit at the consumer unit and verify dead Switch off the circuit breaker for the lighting circuit. Lock it out. Test with a non-contact voltage tester at both the switch location and the ceiling rose to confirm all conductors are dead. Only proceed when confirmed dead.
- Identify and label all conductors at the sensor location before disconnecting the existing switch With the circuit isolated, use a multimeter in resistance mode (or a continuity tester) to identify which conductor is the permanent live feed and which is the switched live return to the lamp. Label each conductor. Also identify the neutral if present.
- Connect the PIR sensor terminals per the manufacturer's wiring diagram PIR sensor terminal labels vary by manufacturer but typically: L or LINE IN = permanent live supply (the live that was feeding the old switch), N = neutral, LOAD or output symbol = switched live going to the lamp holder. Insert conductors into the correct terminals and tighten. Apply dielectric grease to any outdoor-mounted sensor connector.
- Set initial sensor adjustments before restoring power Set TIME (time delay) to minimum for testing — typically fully anticlockwise. Set SENSITIVITY (range/detection distance) to mid-range. If outdoors, set LUX to a mid-position. In full daylight, the LUX inhibit may prevent testing — cover the LUX sensor window with tape during daytime testing, remembering to remove the tape afterwards.
- Restore power and test function in test mode Restore the circuit breaker. Stand within the detection zone and move — the light should switch on. With TIME at minimum, the light should switch off within 2–10 seconds of the last detected motion. If it does not switch on, check lux inhibit (cover the sensor window). If it switches on but immediately off, the relay is dropping out — check load rating compatibility.
- Adjust TIME and SENSITIVITY to desired settings and verify outdoor performance Increase TIME to the desired hold-off period (e.g. 5 minutes for a security light). Adjust SENSITIVITY to the desired detection range — start low and increase until the desired coverage is achieved without false triggering from foliage or passing traffic. At dusk, verify the LUX inhibit releases and the sensor operates in ambient darkness.
Specifications
| Detection technology | Passive Infrared (PIR) — detects thermal radiation differential from moving warm bodies |
|---|---|
| Typical detection angle | 110°–180° horizontal; varies by sensor model and lens type |
| Typical detection range | 6–12 m (adjustable via SENSITIVITY control) |
| Supply voltage (typical) | 230 V AC 50 Hz (confirm sensor specification; some models 120V or 12/24 V DC) |
| Quiescent power consumption (sensor electronics) | 0.5–2 W (continuous, even when light is off) |
| Time delay (hold-off) adjustment range (typical) | 10 seconds to 30 minutes (adjustable via TIME control) |
| Minimum load (relay-switched, conventional) | 40–100 W — must not be exceeded downward for relay sensor; use LED-compatible sensor for LED loads |
| Maximum load (typical relay-switched sensor) | 1 000–2 000 W — confirm sensor rating label |
Safety warnings
- ISOLATE THE CIRCUIT before working on any lighting wiring. A PIR sensor is wired to the live mains supply permanently — even when the connected light is off, the sensor's supply terminals carry mains voltage. Verify dead with a non-contact tester before touching any wiring.
- Verify PIR sensor load rating compatibility before connecting LED luminaires. An undersized minimum load causes relay arc bounce, LED flickering, premature sensor failure, and in some cases fire from sustained arcing at the relay contacts. Use only LED-compatible sensors for LED luminaire control.
- Do not install a PIR sensor rated for indoor use in an outdoor or damp location. Moisture ingress will damage the electronics and cause false triggering, failure, or a shock hazard at the exposed terminals. Use a sensor with the appropriate IP (Ingress Protection) rating for the installation location.
- All lighting circuit wiring, including PIR sensor installation, must be carried out by a qualified electrician and must comply with IEC 60364, BS 7671, NEC Article 410, AS/NZS 3000, or the applicable national wiring standard. Notify the relevant building authority where required.
- False triggering of security lighting can compromise home security by habituating neighbours to the light activating frequently. Adjust sensitivity and detection angle carefully to avoid triggering from trees, foliage moving in wind, passing road vehicles, or small animals.
Tools needed
- Non-contact voltage tester
- Digital multimeter (continuity, resistance, AC voltage)
- Insulated screwdrivers (flat and Phillips)
- Wire stripper
- Drill and fixings (for sensor mounting bracket if wall-mounted)
- Lockout/tagout device for circuit breaker
- Tape measure (for measuring detection coverage zone)
Common mistakes
- Wiring the sensor without neutral available at the sensor location: This is the most common installation error with PIR sensors in switch replacement applications. The existing switch cable often contains only a switched live (both conductors are live conductors in the loop-in system). Without neutral, the sensor electronics cannot operate. Running a new cable with neutral is the correct fix — not improvising connections.
- Exceeding the sensor maximum load rating: Connecting a load greater than the sensor's rated maximum overloads the relay contacts or triac, causing overheating, welded contacts, and fire risk. Check the maximum wattage on the sensor label and never exceed it.
- Installing an indoor IP-rated sensor in an outdoor environment: IP44 sensors (splash-proof) are suitable for covered outdoor locations. Open outdoor locations require IP65 (dust-tight, jet-spray resistant) or higher. Check the sensor IP rating before mounting it outdoors.
- Pointing the sensor toward a heat source: PIR sensors detect changes in infrared radiation. An air conditioning unit, heating vent, or sunny window can cause repeated false triggers. Avoid mounting the sensor where its detection zone sweeps across variable heat sources.
- Not testing LUX control in actual dusk conditions: Setting the LUX control mid-range and assuming it is correct often leads to the light either staying on all day (LUX threshold too high — sensor always thinks it is dark) or never switching on at night (LUX threshold too low). Test and adjust at actual dusk with the installation in its final configuration.
Troubleshooting
- Light does not switch on when person enters detection zone
- Cause: LUX inhibit active (too bright, or LUX threshold set too low), SENSITIVITY set too low (detection range insufficient), sensor supply not reaching the unit, or faulty sensor Fix: Cover the sensor LUX window with tape to bypass the daylight inhibit and test — if the light now switches on, the LUX setting needs adjustment. If still no response, verify mains voltage is present at the sensor L and N terminals. Test SENSITIVITY at maximum range. If sensor has power and sensitivity is maximum but gives no output, the sensor is faulty.
- Light switches on by itself with no person present
- Cause: PIR detection zone sweeping a heat source (sun, vent, heating unit), detection of animals or foliage movement, SENSITIVITY set too high, or sensor facing into direct sunlight Fix: Reduce SENSITIVITY to minimum and test whether false triggers stop — if yes, increase sensitivity gradually until false triggers resume, then back off. Reorient sensor to avoid sweeping heat sources or foliage. If in direct sunlight, use a sensor shade or hood to reduce direct solar gain on the pyroelectric element.
- LED light flickers rapidly when sensor triggers, then turns off
- Cause: PIR sensor minimum load requirement not met by low-wattage LED fitting — relay contacts arc and bounce at the low inductive load Fix: Replace the PIR sensor with an LED-compatible model specifically rated for low minimum loads (0 W or low-load rated). Alternatively, if the installation permits, add a resistive load in parallel with the LED (a phantom load — not recommended as it wastes energy). The correct solution is an LED-compatible sensor.
Frequently asked questions
Why does a PIR sensor need both live and neutral, when a standard switch only uses live?
The PIR sensor contains active electronics: a pyroelectric detector, signal processing circuitry, a relay or triac, and often a lux sensor and timer. All of these require a continuous low-power supply (typically 0.5–2 W). A standard manual switch is a purely passive contact — it needs no power. The PIR sensor's electronics need both live and neutral to form the supply circuit, in addition to the switched output to the lamp.
Can I wire two PIR sensors to control the same light?
Yes — two PIR sensors can be wired in parallel on the switched-live path so that either sensor triggers the light. Connect both sensors' load outputs to the same switched-live going to the lamp. Both sensors must each have their own live and neutral supply. Detection by either sensor energises the light. This is useful for large areas, corridors, or rooms with multiple entry points.
What is the 'LUX' adjustment on a PIR sensor?
The LUX control sets the ambient light threshold below which the sensor is allowed to operate. When ambient light is above the threshold (daytime), the sensor is inhibited and the light will not switch on even if motion is detected. As ambient light drops below the threshold (dusk), the inhibit is released and the sensor responds to motion normally. For outdoor security lighting that should only activate at night, set LUX to a mid-range value and test at dusk.
My PIR sensor switches the light on and it immediately turns off — what is wrong?
The time-delay control (TIME) is set to its minimum value. The sensor correctly detected motion and switched the light on, but the hold-off period expired within seconds. Rotate the TIME adjustment clockwise to increase the hold-off period to the desired duration. If the sensor repeatedly switches on and immediately off in a loop, suspect a faulty sensor — specifically a failing relay or triac that drops out before the timer counts down.
Can I use a PIR sensor with LED lights?
Yes, but verify the sensor's minimum load specification. Many PIR sensors (particularly older relay-switched models) require a minimum load of 40–100 W to operate correctly. A modern LED fitting of 5–10 W falls below this threshold, causing the relay contacts to arc and bounce, the LED to flicker, or the sensor timer to behave erratically. For low-wattage LED loads, use a PIR sensor specifically rated for LED and low-load applications — the specification will show a minimum load of 0 W or state 'LED compatible'.
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