European term for relay.


BACnet is a communications protocol for building automation and control networks. It is an ASHRAE, ANSI, and ISO standard protocol.

Ballast Rating

A rating for Fluorescent and High Intensity Discharge (HID) lighting (Not the same as electronic ballast rating).

C Form Relay

Form C relays are SPDT and break the connection with one throw before making contact with the other (break-before-make).


See Panel


The CE marking certifies that a product has met EU consumer safety, health or environmental requirements.

Circuit Breaker

A circuit breaker is an automatically-operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit.

Class 2 Transformer

A transformer that has a 30VRMS maximum secondary potential under any condition of loading.


Functional Devices Specific – Describes the 3 positions of the override switch. Contact closed, contact open, and relay contact controls load (Auto). See H/O/A, Override


The control side of a relay which creates a magnetic field when voltage is applied to change the state of the contacts.

Control Transformer

A transformer that typically outputs low voltage (12-24 Vac) for control systems.

CT (Current Transformer)

A current transformer (CT) is used for measurement of electric currents.

Current Sensor (Current Transducer)

A current sensor is a device that detects electrical current (AC or DC) in a wire, and generates a signal proportional to it.

Current Switch

A device that detects current flow and closes a contact when current is about the rated trip point.


See Ring

EnOcean Alliance

A consortium of companies dedicated to the advancement of self-powered interoperable wireless building control systems.

External Sensor

An external current ring or clamp that encircles a load wire and, through magnetic coupling, senses the flow. Its output is connected to a Transducer that provides an appropriate output in a Class 2 wiring environment.

General Use/General Purpose

For resistive or light inductive loads.

Gold Flash

Gold coating on the relay contacts to allow the use of dry contact sensing for digital inputs.

H/O/A (Hand-Off-Auto)

Industry standard term for an override switch. See Closed-Open-Auto and Override

HI/LO Voltage Separation

Functional Devices Specific – A physical barrier and compartment allows for Class 2 (low voltage) separation. See T and X series


Horse Power. A rating for motors

I/O Board

Typically refers to a networkable relay module that has various inputs and outputs but without built-in logic capability.

Inductive Rating

“Pilot Duty” A rating for controlling contactors, relays, and solenoids. For Motors – See HP

Inherently Limited

A Class 2 transformer whose maximum power is limited by the winding impedance of the transformer.

Internal Sensor

Connects in series with a load wire to sense current flow. Its output is connected to a Transducer that provides an appropriate output in a Class 2 wiring environment.


Defined in terms of ballast or tungsten.

Load Side

Contact side of the relay.


LonWorks is a networking platform specifically created to meet the needs of control applications. The platform is built on a protocol created by Echelon Corporation for networking devices over media such as twisted pair, power lines, fiber optics, and RF. It is used for the automation of various functions within buildings such as lighting and HVAC.

Modular Relay

See Panel Mount Relay


Functional Devices Specific – A second pole on the Closed-Open-Auto switch allows user to sense the position of the override switch. See H/O/A, Override


Defined in terms of Horse Power (HP).

Multi-Voltage Input

Ability of one unit to accept a wide range of coil voltage inputs.


The National Electrical Code (NEC) is a United States standard for the safe installation of electrical wiring and equipment.

NEMA Rating

Defines the protection level of a housing. For more information, please refer to the NEMA Enclosure Types.


An interconnected system of devices or loads within a building.

Normally Closed Relay (N/C)

A contact that is closed when disconnected from power and opens when power is applied.

Normally Closed Door Switch (N/C)

A door switch that is closed when no outside forces are acting upon it.

Normally Open Relay (N/O)

A contact that is open when disconnected from power and closes when power is applied.

Normally Open Door Switch (N/O)

A door switch that is open when no outside forces are acting upon it.

Override Switch

See Closed-Open-Auto


Short for control panel. An electrical box where controls and relays are installed.

Panel Mount Relay

RIB relay models designed for panel mounting, with terminal input/output connections, sized to fit 4″ or 2.75″ wide plastic track (standard or DIN mount).

Pilot Relay

Functional Devices Specific RIB models rated for 15 Amps and less typically used for piloting/controlling contactors or solenoids, but has high enough power ratings for load control.

Plenum Rating

All UL listed pre-packaged models have a 94-5 V flame rating and are considered acceptable to be used in air circulating applications or plenums.

Polarized Relay

When a DC voltage is used to power the relay, the relay will only be energized if the positive voltage is present on the appropriate input of the relay. These devices are use for monitoring purposes in some fire alarm applications.

Power Relay

RIB models rated for 20 and 30 amp relay applications.


Functional Devices Specific – Ready assembled units saves the installer the time, trouble, and expense of buying separate components and assembling them on the job or in the shop.


Rules determining the format and transmission of data.

Resistive Rating

Ampere rating for electrical heating loads. (Example: Electric water heater and electric baseboard heater)


(Donut ring/Current ring/CT) Used for external current sensing up to 150 amps.


Restriction of the use of certain hazardous substances in electrical and electronic equipment.


Plastic mounting device for installation of modular relays within a control panel.

Standard Ambient

-30 degrees F to 140 degrees F.


Used to describe on/off control of loads.


Material in an enclosure, metal or otherwise, designed for mounting electrical equipment.


A switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another.

T-Style Relay

A relay package that provides HI/LO separation. See HI/LO Separation


Circuitry that converts the voltage coming from the sensor to an appropriate output in a Class 2 wiring environment (usually to a contact output or to a DC voltage output).


A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors – the transformer’s coils.

“True Override”

Functional Devices Specific – A trademark of the RIB line which allows you to manually start/stop the load by controlling the contact side, not the coil side, of the unit. See H/O/A and Override

Tungsten Rating

A rating for incandescent light. (Example: Household lightbulb)

UL Listed

A product that has been evaluated to be compliant with the standards set in place by Underwriters Laboratories, a privately owned, nationally recognized testing laboratory and certification organization.


An uninterruptible power supply (UPS) is an electrical apparatus that provides emergency power to a load when the input power source, typically the utility mains, fails.

Voltage Transient Suppression

Reducing relay coil transients that might affect a control device.