1 Scope

1.1 As noted in Low Voltage Transformers – Part 1: General Requirements, UL 5085-1, or CSA C22.2 No. 66.1,  Low Voltage Transformers – Part 1: General Requirements, the requirements in Part 3 cover Class 2 transformers for use with Class 2 circuits in accordance with the National Electrical Code, ANSI/NFPA 70, or the Canadian Electrical Code, Part I, CSA C22.1. They are intended for connection to essentially sinusoidal supply sources.

Advisory Note: For transformers intended for use in the United States, these requirements also cover Class 3 transformers for use with Class 3 circuits in accordance with the National Electrical Code, ANSI/NFPA 70, unless otherwise specified in this standard. See Annex d for Class 3 requirements.

1.3 In addition to the items specified in Clause 1.3 of Part 1, the requirements of Part 3 do not cover:

a)    Power supplies (a transformer provided with a rectifier is considered a power supply);

b)    Toy transformers;

c)    Cord and plug connected transformers other than Class 3;

d)    Direct plug-in transformers;

e)    Transformers intended for use in audio, radio, or television type appliances; or

f)     Other special types of transformers covered in requirements for other electrical devices or appliances.

Advisory Note: The requirements of Part 3 do not cover transformers intended for use in the United States having a nominal primary rating of more than 600 V and transformers having overvoltage taps rated over 660 V.

1.7 This part is intended to be used in conjunction with Part 1. The numbering of the clauses in Part 3 corresponds to the numbered clauses in Part 1. The requirements in Part 1 apply unless modified by Part 3.

1.8 A Class 2 transformer that includes a separate current-limiting impedance such as a resistor or a positive temperature coefficient device (PTC) is covered by these requirements.

1.9 A Class 2 transformer that includes a resonance regulating circuit is covered by these requirements.

• Cover
• Transmittal
• UL Harmonized Standard Title Page
• Table of Contents
• PART 3: CLASS 2 AND CLASS 3 TRANSFORMERS
• 1 Scope
• 4 Construction
• 6 Enclosure
• 6.1 General
• 8 Connections
• 8.2 Wiring terminals
• 8.5 Leads
• 11 Spacings and Insulation
• 11.2 Insulating material for mounting of low voltage live parts
• 11.3 Coil insulation
• 11.4 Insulation in lieu of spacings
• 11.5 Spacings
• 11.6 Separation of internal wiring circuits
• 12 Switches, Protective Devices, and Wiring Devices
• 12.3 Protective devices
• 12.4 Separate current-limiting impedances
• 12.5 Overtemperature protective devices
• 17 Markings
• 17.1 General
• 17.3 Ratings
• 17.4 Details
• 18 Tests
• 27 Open Circuit Secondary Voltage Test
• 28 Output Current and Power Test
• 28.1 Maximum current output of inherently limited transformers
• 28.2 Maximum current of non-inherently limited transformers
• 28.3 Maximum power of non-inherently limited transformers
• 29 Calibration Test of Overcurrent Protective Devices
• 30 Rated Secondary Current Test
• 31 Rated Output Heating Test
• 32 Dielectric Voltage-Withstand Test
• 32.1 General
• 32.2 Induced potential
• 33 Overload Heating Test
• 33.1 General
• 33.2 Procedure
• 34 Dielectric Voltage-Withstand After Overload Heating Test
• 35 Overload Test of Overcurrent or Overtemperature Protective Devices
• 36 Endurance Test of Automatically Reset Overtemperature Protective Devices
• 37 Strain Relief Test
• Annex A (Informative)
• Annex C (Informative)
• Annex D (Normative)