UL Standard for Safety Low Voltage Transformers – Part 3: Class 2 and Class 3 Transformers
|Publication Date:||17 April 2006|
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.
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.
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.
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.
A Class 2 transformer that includes a resonance regulating circuit is covered by these requirements.