Occupancy Sensor Symbol
Definition: The Occupancy Sensor symbol represents an electronic detection device that automatically controls lighting or HVAC systems based on the presence or absence of people in a space, depicted as a rectangular block with an input pin (In, connected to the power or control circuit) and an output pin (Out, switching the controlled load), conforming to building automation standards including ANSI/ASHRAE Standard 90.1 and IEC 60669-2-1.
Also known as: occupancy detector, presence sensor, vacancy sensor, motion-controlled switch, PIR occupancy switch.
What the Occupancy Sensor symbol means
The Occupancy Sensor symbol denotes a control device that monitors a space for human presence and automatically switches loads on when occupancy is detected and off after a configurable time-delay when the space becomes vacant. Most commercial occupancy sensors combine passive infrared (PIR) detection for motion with ultrasonic or microwave sensing for minor motion (seated workers), providing dual-technology coverage for reliable detection.
In building electrical and lighting control wiring diagrams, the Occupancy Sensor symbol conveys an automatic switching point that replaces a manual wall switch. The In pin represents the line-voltage or low-voltage control input, and the Out pin represents the switched output to luminaires or HVAC contactors. Occupancy sensors are mandated by ASHRAE 90.1 and international energy codes for most commercial spaces to reduce lighting energy consumption.
How to identify the Occupancy Sensor symbol
The Occupancy Sensor symbol is drawn as a rectangular block labelled 'Occupancy Sensor' or 'OS', with an input pin (In) on the left and an output pin (Out) on the right. Some representations include a detection-arc or lens icon inside the block. It is distinguished from a simple motion sensor by the explicit load-switching output pin and the energy-control context in which it appears in wiring diagrams.
Function in a circuit
The Occupancy Sensor detects human presence using one or more of: passive infrared (PIR, detects thermal radiation from moving warm bodies), ultrasonic (detects movement via Doppler shift of transmitted ultrasonic waves), or microwave (radar-based Doppler motion detection). When occupancy is detected, the output relay or solid-state switch closes to energise the controlled load. After a programmable time delay (typically 5 seconds to 30 minutes) without further detection, the output opens to de-energise the load, providing automatic energy saving without occupant intervention.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60669-2-1 defines electronic switches including occupancy sensor switches for household and similar fixed electrical installations. IEC 60617 does not have a dedicated occupancy sensor glyph; the sensor is drawn as a generic switch or control block. EN 15193 covers energy performance requirements for lighting control including occupancy sensing. |
|---|---|
| ANSI/IEEE 315 | ANSI/ASHRAE Standard 90.1 (Energy Standard for Buildings) mandates automatic shutoff controls including occupancy sensors for commercial spaces. UL 508 covers industrial control equipment. ANSI Y32.2 / IEEE 315 has no dedicated occupancy sensor symbol; the device is shown as a labelled control block. |
| Key difference | Both IEC and ANSI/IEEE represent the occupancy sensor as a labelled block or controlled switch symbol; there is no standardised unique glyph. IEC 60669-2-1 provides specific electrical requirements for the device. |
Terminals / pins
| Pin | Name |
|---|---|
| in | In |
| out | Out |
Typical values
Detection range: 6–20 m (PIR), 360° wide-angle or 60–110° directional. Time delay: adjustable 1 second to 30 minutes. Ambient light threshold: 0–50 lux (daylight harvesting variants). Supply voltage: 120 V or 277 V AC (line-voltage), or 12–24 V DC (low-voltage). Switched load: up to 800–1200 VA (line-voltage relay), or dry-contact output for low-voltage systems. Sensitivity: adjustable for minor motion (seated workers) vs. major motion only.
Where the Occupancy Sensor symbol is used
- Commercial office lighting control where lights automatically shut off after a time delay when a workstation is vacant, meeting ASHRAE 90.1 energy code requirements
- Conference room and private office lighting where ceiling-mounted dual-technology occupancy sensors (PIR + ultrasonic) detect minor motion of seated occupants
- Corridor and stairwell lighting where sensors dim lights to a standby level and bring to full brightness when occupancy is detected
- HVAC zone control where an occupancy sensor switches a 24 V thermostat signal to change setpoints between occupied and unoccupied modes
- Residential bathroom and utility room ceiling sensors that switch lights on automatically and off after a time delay when the space is vacant
- Warehouse and industrial lighting where high-bay fixture occupancy sensors reduce energy consumption during unoccupied aisles
Example
In a commercial office single-circuit lighting control, a Lutron LOS-WDT-WH ceiling-mounted dual-technology occupancy sensor connects its In pin to the 120 V hot conductor and its Out pin to the hot wire feeding eight 2×4 LED troffers. When any person enters the room, the PIR detector triggers the relay to close within 0.5 seconds, illuminating the lights. After 15 minutes without detected motion, the relay opens and the lights turn off automatically.
Key facts
- Occupancy sensors use passive infrared (PIR) technology to detect the thermal radiation of moving warm bodies, ultrasonic technology for Doppler detection of minor motion, or both (dual-technology) for reliable detection of seated occupants.
- ANSI/ASHRAE Standard 90.1 mandates automatic shutoff controls including occupancy sensors for classrooms, conference rooms, private offices, restrooms, and corridors in commercial buildings.
- The Occupancy Sensor symbol has two pins in schematic representations: In (power/control input) and Out (switched load output); the internal detection electronics are abstracted within the block.
- Time delay is adjustable from seconds to 30 minutes; most energy codes require a maximum 20-minute timeout for lighting occupancy controls.
- Line-voltage occupancy sensors (120/277 V) directly switch the lighting circuit; low-voltage sensors (12–24 V DC) provide a dry-contact or 0–10 V signal to a lighting controller or relay panel.
- Vacancy sensors require manual turn-on (pressing a button) and turn off automatically — this provides greater energy savings than auto-on occupancy sensors by preventing false triggers from HVAC airflow or passersby.
- Dual-technology sensors combining PIR and ultrasonic detection reduce both false-on (someone walking past a window) and false-off (a seated person not moving enough to trigger PIR alone) events.
Frequently asked questions
What does the occupancy sensor symbol mean in a wiring diagram?
The Occupancy Sensor symbol represents an automatic lighting or HVAC control device that detects human presence and switches a load on when occupied and off after a time delay when vacant. It conforms to IEC 60669-2-1 and ANSI/ASHRAE 90.1 energy code requirements for automatic shutoff controls.
What does the occupancy sensor symbol look like?
The Occupancy Sensor symbol is a rectangular block labelled 'Occupancy Sensor' or 'OS', with an input pin (In) on one side and an output pin (Out) on the other. A lens or detection-arc icon may appear inside the block. It appears in building electrical wiring diagrams at the lighting circuit switching point.
What is the difference between an occupancy sensor and a vacancy sensor?
An occupancy sensor automatically turns lights on when a person enters the space and off after a time delay when the space is vacant — no manual action required. A vacancy sensor turns off automatically when vacant but requires a manual press to turn lights on. Vacancy sensors save more energy because they prevent auto-on in already-illuminated spaces.
What detection technologies do occupancy sensors use?
Occupancy sensors use passive infrared (PIR) to detect thermal radiation from moving people, ultrasonic to detect minor movements (breathing, typing) via Doppler shift, and microwave (radar) for through-partition detection. Dual-technology sensors combine PIR and ultrasonic for reduced false triggers, and are required by some energy codes for private offices and conference rooms.
What standard mandates occupancy sensors in commercial buildings?
ANSI/ASHRAE Standard 90.1 (Energy Standard for Buildings) mandates automatic lighting shutoff controls including occupancy sensors for offices, classrooms, conference rooms, restrooms, and corridors in commercial buildings in the United States. In Europe, EN 15193 covers energy performance of lighting including occupancy-based control.
What is the time delay setting on an occupancy sensor?
Occupancy sensor time delay is adjustable, typically from a few seconds to 30 minutes. Energy codes such as ASHRAE 90.1 require a maximum 20-minute timeout for automatic lighting shutoff. Shorter delays (5–10 minutes) are used in restrooms and copy rooms; longer delays (15–30 minutes) in private offices where brief absences (coffee break) should not trigger a shutoff.
What is the difference between a line-voltage and low-voltage occupancy sensor?
A line-voltage occupancy sensor (120 V or 277 V AC) contains an internal relay that directly switches the lighting circuit hot conductor — it acts as a self-contained switch replacement. A low-voltage sensor (12–24 V DC) provides only a dry-contact or 0–10 V control output that connects to a relay panel, lighting controller, or building automation system; it requires separate power wiring.
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