UL 873
Standard for Temperature-Indicating and -Regulating Equipment

DETAILS
Edition Number:12SCC Approved:--
Edition Date:2007-11-16DOD Approved: 1992-01-17
Price Code:DANSI Approved: --
Type:ulstd

  • SCOPE

    1 Scope

    1.1 These requirements cover electrical equipment for control of air-conditioning, heating, cooking, refrigeration, and humidity, rated 600 volts or less, to be used in ordinary locations in accordance with the National Electrical Code, NFPA 70.

    1.2 These requirements cover general-use equipment for field-installation and controls intended to be factory installed on or in certain appliances as safety, limiting, or operating controls. These controls respond directly or indirectly to changes in temperature, humidity, or pressure to effect control of equipment or appliance operation. Devices covered by these requirements include:

    a)    Refrigeration Controllers – Humidistats for factory installation on or in refrigeration equipment; pressure, temperature, pneumatic pressure, motor, timer, bimetallic-heater, magnetically-operated controls, and the like, and combinations thereof in control panels with or without transformers. See 1.4.

    b)    Industrial Operating Controls – Temperature controllers for industrial, farm, and boiler room applications; snow melting controls; return-duct humidistats; humidity controllers; pneumatic pressure regulators; transformer (low-voltage secondary) relays; pneumatic pressure, bimetallic-heater, motor, timer, and magnetically operated sequence switches; stoker controls; indicating and recording controls; and motor operators for actuating air dampers. These requirements do not cover output connected apparatus such as dampers, linkages, or valves.

    c)    Residential Operating Controls – Room thermostats, room humidistats, and other operating controls for residential heating and cooling appliances.

    d)    Controls for Factory Installation on or in Appliances –

    1)    Controls as mentioned in (a) – (c) but specifically intended for use on, in, or as a part of the end-use equipment.

    2)    Electric water-heater controls intended to regulate or limit water temperature.

    3)    Other controls including door-interlock thermostats for self-cleaning ovens; baseboard heater temperature-limiting controls; humidifier controls; fan thermostats; and temperature-regulating and -limiting thermostats for electric heating equipment such as clothes dryers, air heaters, household and commercial cooking appliances, beauty-parlor equipment, steam and dry bath heaters, and ranges (controlling oven or surface elements).

    1.3 Certain safety controls, and safety control circuits on operating controls, are investigated under the requirements in this standard, insofar as they apply, and also under the applicable requirements for limit controls.

    1.4 The following devices are among those considered to be refrigeration controllers:

    a)    A control that either directly or indirectly controls the starting and stopping of a compressor motor of refrigeration or air-conditioning equipment because of variations in temperature, pressure, refrigerant level, or the like.

    b)    A pressure limiting device and a defrost temperature-limiting device for refrigeration or air-conditioning equipment.

    c)    An auxiliary device, such as a defrost timing control, a defrost temperature regulating control, a start winding relay for a compressor motor, a control or defrost or heat pump change-over, fan or pump motor, vane or load capacity regulator, or a similar device that primarily serves refrigeration or air-conditioning equipment.

    d)    A control panel that, incorporates one or more of the functions described in (a) – (c) for programming refrigeration or air-conditioning equipment.

    1.5 A wall-mounted room thermostat not intended for mounting in or on refrigeration or air-conditioning equipment is investigated as a thermostat and not as a refrigeration controller.

    1.6 Industrial temperature-indicating and -regulating controls include controls that are intended, among other applications, for installation in or on industrial apparatus, or for boiler or furnace room, farm, outdoor, and comparable locations that may not always be clean and dry.

    1.7 A residential control is one intended for indoor comfort control use in clean, dry, nonindustrial environments, such as dwellings, offices, and stores.

    1.8 A humidistat is investigated in the same manner as a thermostat.

    1.9 Requirements for controls intended to be factory installed on or in appliances may include requirements appropriate for the end-use appliance. The spacing requirements for several such controls are specified in Table 32.1.

    1.10 These requirements do not cover primary safety or limit controls for gas, oil, or electric-fired central-heating furnaces or boilers; duct heaters; oil or gas burners; or stokers; nor do they cover controls for oil pumps and oil level regulators; boiler-feed or low-water cut-offs; or furnace fan or boiler circulators.

    1.11 These requirements do not cover low-voltage thermostats, damper controls or similar devices intended for connection only to a low-voltage circuit of limited power supplied by a primary battery or by a Class 2 transformer. An assembly consisting of a line-voltage transformer with a low-voltage secondary incorporated as an integral part of a control, such as a thermostat or a damper control, is considered to be within the scope of these requirements. See 6.1.

    1.12 A product that contains features, characteristics, components, materials, or systems new or different from those covered by the requirements in this standard, and that involves a risk of fire or of electric shock or injury to persons shall be evaluated using appropriate additional component and end-product requirements to maintain the level of safety as originally anticipated by the intent of this standard. A product whose features, characteristics, components, materials, or systems conflict with specific requirements or provisions of this standard does not comply with this standard. Revision of requirements shall be proposed and adopted in conformance with the methods employed for development, revision, and implementation of this standard.

  • TABLE OF CONTENTS
    Expand All

    • Cover
    • Transmittal
    • Table of Contents
      • Body
        • INTRODUCTION
          • 1 Scope
          • 2 Glossary
          • 3 Units of Measurement
          • 4 Components
          • 5 References
        • CONSTRUCTION
          • 5A Components
            • 5A.1 General
            • 5A.2 Attachment plugs, receptacles, connectors, and terminals
            • 5A.3 Batteries
            • 5A.4 Electrical boxes and raceways
            • 5A.5 Capacitors, filters and surge protective devices
            • 5A.6 Thermistors and thermal links
            • 5A.7 Cords and cables
            • 5A.8 Gaskets and seals
            • 5A.9 Ground-fault, arc-fault, and leakage current detectors/interrupters
            • 5A.10 Heaters and heating elements
            • 5A.11 Insulation systems
            • 5A.12 Light sources and associated components
            • 5A.13 Marking and labeling systems
            • 5A.14 Overcurrent protection
            • 5A.15 Power supplies
            • 5A.16 Printed wiring boards
            • 5A.17 Power switching semiconductors, optical isolators, and electronic components
            • 5A.18 Supplemental insulation, insulating bushings, and assembly aids
            • 5A.19 Transformers
            • 5A.20 Valves (electrically operated) and solenoids
          • 6 General
          • 7 Frame and Enclosure
            • 7.1 General
            • 7.2 Accessibility of live parts
            • 7.3 Covers
            • 7.4 Transformers
            • 7.5 Cast metal
            • 7.6 Sheet metal
            • 7.7 Polymeric
            • 7.8 Windows
            • 7.9 Room thermostats
            • 7.10 Openings
            • 7.11 Screens and expanded metal
            • 7.12 Wiring openings
            • 7.13 Raintight and rainproof enclosures
          • 8 Mounting
          • 9 Parts Containing Liquid Metal
          • 10 Adjustment Stop
          • 11 Operating Mechanism
          • 12 Reset Mechanism – Limiting Control
          • 13 Means for Calibration
          • 14 Protection Against Corrosion
          • 15 Insulating Material
          • 16 Supply Connections
            • 16.1 General
            • 16.2 Equipment permanently connected electrically
            • 16.3 Cord and plug connected portable equipment
            • 16.4 Stationary equipment
          • 17 Current-Carrying Parts
          • 18 Switches
          • 19 Internal Wiring
          • 20 Low-Voltage External Wiring Requirements
          • 21 Grounding
            • 21.1 General
            • 21.2 Grounding means
            • 21.3 Equipment permanently connected electrically
            • 21.4 Terminals and leads
          • 22 Bonding of Internal Parts
            • 22.1 General
            • 22.2 Construction and connection
          • 23 Protection of Users and Service Personnel
            • 23.1 General
            • 23.2 Mechanical servicing
            • 23.3 Electrical servicing
          • 24 Protection Against Injury to Persons
            • 24.1 Scope
            • 24.2 Sharp corners and edges
            • 24.3 Moving parts
            • 24.4 Temperature
            • 24.5 Mounting devices
            • 24.6 Strength of parts
          • 25 Capacitors
          • 26 Fuseholders
          • 27 Receptacles
          • 28 Protection of Control-Circuits
            • 28.1 Conductors
            • 28.2 Transformers
          • 29 Short-Circuit, Ground-Fault, Overload, and Thermal Protection
          • 30 Mercury-Tube Switches
          • 31 Coil Windings
          • 32 Spacings
            • 32.1 General
            • 32.2 Line-voltage circuits
            • 32.3 Magnet coil windings
            • 32.4 Low-voltage circuits
            • 32.5 Isolated limited secondary circuits
          • 33 Alternate Spacings – Clearances and Creepage Distances
          • 34 Wiring Space
          • 35 Separation of Circuits
            • 35.1 Separation between different internal wiring circuits (factory-installed conductors)
            • 35.2 Separation between different field wiring circuits (field-installed conductors)
            • 35.3 Separation between field wiring circuits (field-installed conductors) and internal wiring circuits (factory-installed conductors)
            • 35.4 Segregation methods
            • 35.5 Separation methods
          • 36 Class 2 Power Sources and Circuits
            • 36.1 General
            • 36.2 Interconnections
            • 36.3 Circuits
            • 36.4 Transformers
            • 36.5 Power limiting components
            • 36.6 Overcurrent protection components
          • 37 Barriers
        • PERFORMANCE
          • 38 General
            • 38.1 Samples
            • 38.2 Electric heat thermostat
            • 38.3 Controller
            • 38.4 Baseboard heater controls
            • 38.5 Relays
            • 38.6 Electric range controls
            • 38.7 Auxiliary electric range controls
            • 38.8 Conditioning at elevated temperature – household range control switch body
            • 38.9 Temperature-limiting controls for electric ranges
            • 38.10 Ice and Snow-Melting Equipment Controls
          • 39 Power Input
          • 40 Temperature Test
          • 41 Leakage Current Test
          • 42 Leakage Current Following Humidity Conditioning Test
          • 43 Operation Test
          • 44 Calibration-Verification Test
          • 45 Overload Test
          • 46 Endurance Test
          • 47 Dielectric Voltage-Withstand Test
            • 47.1 General
            • 47.2 Induced potential
            • 47.3 Induced potential repeated
          • 47A Abnormal Operation Test
            • 47A.1 General
            • 47A.2 Abnormal Switching Test
          • 48 Volt-Ampere Capacity Test
          • 49 Burnout Test
          • 50 Short Circuit Test
            • 50.1 Mercury-tube switch
            • 50.2 Conductor
            • 50.3 Equipment for motor control
          • 51 Parts Containing Liquid Metal Test
          • 52 Two-Step Operation Surface-Unit Controls Test
            • 52.1 General
            • 52.2 Push- and pull-and-turn controls
            • 52.3 Other types of controls
          • 53 Strain-Relief Test
          • 54 Accelerated Aging Tests on Gaskets, Sealing Compounds, and Adhesives
          • 55 Metallic Coating Thickness Test
          • 56 Rain Test
          • 57 Time-Calibration Verification Test
            • 57.1 General
            • 57.2 Bimetal-heater design
            • 57.3 Initial time-calibration-verification Test I
            • 57.4 Initial time-calibration-verification Test II
            • 57.5 Endurance
            • 57.6 Time-verification and dielectric voltage-withstand tests after endurance
            • 57.7 Other designs
          • 58 Snap-On Covers Test
          • 59 Bonding Conductor Tests
            • 59.1 Overcurrent
            • 59.2 Resistance
          • 60 Permanence of Marking Test
            • 60.1 General
            • 60.2 Oven-aging
            • 60.3 Immersion
            • 60.4 Standard-atmosphere
            • 60.5 Unusual condition exposure
            • 60.6 Humidity
          • 61 Strength of Adjustment Stop Test
          • 62 Polymeric Materials Tests
            • 62.1 General
            • 62.2 Conduit connections
            • 62.3 Knockouts
          • 63 Class 2 Power Sources and Circuit Tests
            • 63.1 General
            • 63.2 Ambient air temperature
            • 63.3 Open-circuit secondary voltage
            • 63.4 Maximum current of inherently limited power source
            • 63.5 Maximum current of not inherently limited power source
            • 63.6 Maximum power of not inherently limited power source
            • 63.7 Calibration of overcurrent-protective devices
            • 63.8 Rated secondary output
            • 63.9 Rated output heating
            • 63.10 Dielectric voltage withstand
            • 63.11 Component breakdown
            • 63.12 Overload heating
            • 63.13 Repeat dielectric voltage withstand
            • 63.14 Overload of overcurrent- or overtemperature-protective devices
            • 63.15 Endurance of automatic-reset overtemperature-protective devices
          • 64 Isolated-Limited Secondary and Non-Class 2 Circuits Tests
        • MANUFACTURING AND PRODUCTION TESTS
          • 65 Details
            • 65.1 General
            • 65.2 Marked-off position
          • 66 Grounding Continuity
        • RATING
          • 67 General
          • 68 Class 2 Power Sources and Circuits
        • MARKING
          • 69 General
          • 70 Wiring
          • 71 Calibration Setting
          • 72 Elevated Air Temperature
          • 73 Location
          • 74 Cautionary Markings
          • 75 Class 2 Power Sources and Circuits
          • 76 Instructions
        • SPECIAL-PURPOSE DEVICES
          • 77 Scope
          • 78 Fan/Heat Sequencers
            • 78.1 Scope
            • 78.2 General
            • 78.3 Performance
            • 78.4 Mechanical and production tests
            • 78.5 Rating
            • 78.6 Marking
          • 79 Fluorescent-Lamp-Ballast Protectors
            • 79.1 Scope
            • 79.2 General
            • 79.3 Construction
            • 79.4 Performance
            • 79.5 Manufacturing and production tests
            • 79.6 Marking
          • 80 Control-Circuit Temperature-Limiting Devices for Temperature Protection of Enclosures of Motors and Generators for Use in Hazardous Location
            • 80.1 Scope
            • 80.2 General
            • 80.3 Construction
            • 80.4 Performance
            • 80.5 Manufacturing and production tests
            • 80.6 Rating
            • 80.7 Marking
          • 81 Single-Operation Devices
            • 81.1 Scope
            • 81.2 General
            • 81.3 Operation mechanism
            • 81.4 Construction
            • 81.5 Performance
            • 81.6 Manufacturer's inspection and test program
            • 81.7 Ratings
            • 81.8 Marking
          • 82 Thermal Protective Devices for Lighting Fixtures
            • 82.1 Scope
            • 82.2 Enclosures
            • 82.3 Accessibility
            • 82.4 Open hole
            • 82.5 Insulating materials
            • 82.6 Wiring connections
            • 82.7 Mounting hardware
            • 82.8 Spacings
            • 82.9 Performance
            • 82.10 Manufacturing and production-line tests
            • 82.11 Ratings
            • 82.12 Markings
          • 83 Controllers for Solar-Energy Systems
            • 83.1 Scope
            • 83.2 Supply connections
            • 83.3 Marking
            • 83.4 Instructions
          • 84 Temperature-Regulating Thermostats for Household Drip-Type Coffee Makers
            • 84.1 Scope
            • 84.2 Glossary
            • 84.3 Construction
            • 84.4 Performance
            • 84.5 Ratings
            • 84.6 Markings