1.1 Transformers covered by these requirements, herein called Class 2 or Class 3 transformers, are for use with Class 2 or Class 3 circuits, respectively, in accordance with the National Electrical Code, ANSI/NFPA 70. They are intended for connection to essentially sinusoidal supply sources. Permanently connected transformers are rated 600 volts or less, and cord and plug connected transformers are rated 120 volts or less.

1.2 A Class 2 or Class 3 transformer that is inherently limited has an impedance within the transformer that limits the current output to a particular maximum value. It may or may not be provided with a thermostat or other temperature sensitive device to limit its maximum temperature.

1.3 A Class 2 or Class 3 transformer that is not inherently limited does not have an impedance to limit the maximum current output to a specified value. However, the maximum power output is limited by an overcurrent-protective device.

1.4 A Class 2 or Class 3 transformer that includes a separate current-limiting impedance, such as a resistor or a positive temperature coefficient device (PTC), is covered by these requirements.

1.5 A Class 2 transformer has a 30-volt rms maximum secondary potential under any condition of loading or open circuit.

1.6 A Class 2 or Class 3 transformer that includes a resonance regulating circuit is covered by these requirements.