Class 1 Circuits 

Class 2 and Class 3 Circuits

For Class 2 Circuits:
Power Supply generally limited to 100 Volt-amperes and maximum voltage of 30 volts.

For Class 3 Circuits:
Power Supply generally limited to 100 Volt-Amperes and maximum voltage of 100 Volts. 
 
 
 
 
 
 
 

Power-Limited Circuits

Remote-Control and Signaling Circuits

Requirements: Shall be 

1. 30 Volts or Less
2. 1000 Volt-amperes or Less
3. Transformers Protected per Article 450
4. Power Sources other than Transformers - limited to 2500 VA.
5. Power Sources other than Transformers Fault Current limited to 10,000 VA for 1 minute or less
6. Power Sources other than Transformers - overcurrent protection limited to 167 % VA of Source divided by Volts

1. 600 Volts or Less
2. No Limit on Power Source Volt-Amperes
3. Transformers per Article 450