The building automation industry runs on more than just wires and relays; it runs on specialized knowledge. With evolving technologies like IoT-enabled controls, BACnet networks, smart sensors, and energy management systems, understanding the right terms is critical for seamless design, installation, and maintenance.
That’s why we created this comprehensive Building Automation Terminology Guide. Whether you’re a contractor, engineer, or facility manager, this resource explains the essential terms you’ll see in our literature and across the industry. Bookmark it, share it with your team, and return whenever you need a quick reference.
Functional Devices has been a trusted name in building automation for over 50 years. Known for our RIB® relays and other innovative solutions, we design products that simplify installation, cut costs, and boost system reliability.
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Building Automation Terminology Guide
Terms are organized by category:
Protocols & Standards
- BACnet. A communications protocol for building automation and control networks.
- LonWorks. A networking platform for control applications over twisted pair, power lines, fiber optics, and RF.
- EnOcean Alliance. A consortium advancing self-powered, interoperable wireless building control systems.
- NEC. The National Electrical Code governing safe electrical installation.
- CE. Certification indicating a product meets EU consumer safety, health, or environmental requirements.
- RoHS. Restriction of hazardous substances in electrical/electronic equipment.
- UL Listed. Certification showing a product meets Underwriters Laboratories safety standards.
- NEMA Rating. Defines enclosure protection levels.
Relays & Switching
- Actuator. European term for relay.
- C Form Relay (Form C). SPDT relay that breaks one throw before making contact with the other.
- H/O/A (Hand-Off-Auto). Override switch with three positions.
- Closed-Open-Auto. Functional Devices’ three-position override switch option.
- Pilot Relay. RIB models rated 15 A or less for controlling contactors or solenoids.
- Power Relay. RIB models rated for 20–30 A applications.
- T-Style Relay. Relay with HI/LO separation.
- True Override. Allows manual start/stop of the load by controlling the contact side.
Sensors & Current Measurement
- CT (Current Transformer). Measures electric current in a conductor.
- Current Sensor/Transducer. Detects AC or DC current and outputs a proportional signal.
- Current Switch. Closes a contact when current flow exceeds a set trip point.
- External Sensor (Ring). Encircles a load wire to sense current flow.
- Internal Sensor. Connects in series to sense current flow directly.
- Ring/Donut. External current sensing up to 150 A.
Transformers & Power
- Class 2 Transformer. Transformer with 30 VRMS maximum secondary potential.
- Control Transformer. Provides low voltage (12–24 VAC) for control systems.
- Inherently Limited. Class 2 transformer limited by winding impedance.
- Transformer. Transfers energy from one circuit to another via induction.
- UPS (Uninterruptible Power Supply). Provides emergency power when mains fail.
Lighting & Load Control
- Ballast Rating. For fluorescent and HID lighting.
- Tungsten Rating. For incandescent light.
- Lighting. Defined in terms of ballast or tungsten loads.
- Load Side. Contact side of the relay.
- Start/Stop. On/off control of loads.
Components & Hardware
- Coil. The control side of a relay.
- I/O Board. Relay module with multiple inputs/outputs but no built-in logic.
- Modular Relay / Panel Mount Relay. Designed for DIN or snap track mounting.
- Panel / Can. Electrical box housing controls and relays.
- Subpanel. Material in an enclosure designed for mounting electrical equipment.
- Snaptrack. Plastic mounting device for modular relays.
Additional Terms
- Gold Flash. Gold coating on relay contacts for dry contact sensing.
- Monitor. Allows sensing of override switch position.
- Multi-Voltage Input. Ability to accept a wide range of coil voltages.
- Polarized Relay. DC relay energized only with correct polarity.
- Plenum Rating. Acceptable for use in air-circulating spaces.
- Protocol. Rules governing data format and transmission.
- Resistive Rating. Amp rating for heating loads.
- Voltage Transient Suppression. Reduces coil transients affecting control devices.
- Motor / HP Rating. Defines motor horsepower and relay capability.
Partner with Building Automation Experts
Clear communication drives better design, safer installations, and more reliable building automation systems. By familiarizing yourself with these terms—ranging from relays and actuators to NEMA ratings and BACnet protocols—you’ll make faster, more informed decisions on every project.
If you have additional terms you’d like us to add, or want help choosing the right Functional Devices product for your application, reach out to our team anytime. We’re here to support your success.