UL 5085-1:2018-01 LOW Voltage Transformers – Part 1: General Requirements.
1.1 These requirements cover the following types of transformers:
a) Air-cooled transformers and reactors for general use;
b) General purpose autotransformers;
c) Ferroresonant transformers;
d) Class 2 and Class 3 transformers (which are evaluated in accordance with Part 3);
e) Cord-connected transformers (which are evaluated in accordance with Part 2);
f) Transformers incorporating overcurrent or over-temperature protective devices, transient voltage surge protectors, or capacitors; and
g) Permanently-connected transformers.
1.2 These transformers are intended to be used in accordance with the National Electrical Code, ANSI/NFPA 70, or CSA C22.1, the Canadian Electrical Code, Part I. The Canadian Electrical Code defines low voltage as any voltage from 31 to 750 V inclusive and high voltage as any voltage above 750
V. The National Electrical Code, ANSI/NFPA 70, defines low voltage as any voltage up to 600 V, nominal. Therefore, low voltage transformers intended for use in Canada may be rated above 600 V up to 750 V. Low voltage transformers intended for use in the United States are rated up to 600 V. Where information in clauses and tables in this standard reference voltage ranges, the limit of 600 V applies in the United States, while the limit of 750 V applies in Canada.
1.3 The standard does not cover the following transformers:
a) Direct plug-in types;
d) Variable voltage (Variac);
e) Low voltage landscape;
f) Swimming pool and spa:
h) High intensity lighting;
j) Fluorescent lamp types;
k) Transformers for welders;
m) Transformers intended for use in the United States with a nominal primary rating of more than 600 V;
n) Transformers incorporating rectifying or waveshaping circuitry;
o) Transformers for use with radio- and television-type appliances;
p) Transformers intended for use in the United States having overvoltage taps rated over 660V;
q) Autotransformers used in industrial control equipment, which are evaluated in accordance with the requirements of the Standard for Industrial Control Equipment, UL 508, or CSA C22.2 No. 14, Industrial Control Equipment; and
r) Other special types of transformers covered in requirements for other electrical devices or appliances.
1.4 Part 1, as well as Part 2 and Part 3, establish the characteristics, construction, operating conditions, markings, and test conditions for each type of transformer.
1.5 The requirements in this standard may be modified by requirements in an end product standard if a transformer is intended for use only as a component in other equipment.
2.1 The following definitions apply in this standard:
2.1.1 CLASS 2 TRANSFORMER — A transformer that has a 30 V rms maximum secondary potential
under any condition of loading.
Note: The impedance within an inherently-limited transformer limits the current output to a particular maximum value.
Maximum power is limited by winding impedance (inherently limited) or by overcurrent protection (not-inherently limited).
It may or may not be provided with a thermostat or other temperature sensitive device to limit its maximum temperature.
A not-inherently limited Class 2 transformer is provided with overcurrent protection to limit the maximum power output.
2.1.2 CLASS 3 TRANSFORMER — A transformer that has a secondary potential over 30 V rms and less than 100 V for inherently-limited transformers, or less than 150 V for not-inherently limited transformers.UL 5085-1 pdf download.