Class 1, 2, 3 circuits
- Thread starter olinga1
- Start date
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pierre
Senior Member
- Location
- Westchester County, New York
Re: Class 1, 2, 3 circuits
From the 2002 NEC:
"Class 1 Circuit. The portion of the wiring system between the load side of the overcurrent device or power-limited supply and the connected equipment. The voltage and power limitations of the source are in accordance with 725.21.
Class 2 Circuit. The portion of the wiring system between the load side of a Class 2 power source and the connected equipment. Due to its power limitations, a Class 2 circuit considers safety from a fire initiation standpoint and provides
acceptable protection from electric shock.
Class 3 Circuit. The portion of the wiring system between the load side of a Class 3 power source and the connected equipment. Due to its power limitations, a Class 3 circuit considers safety from a fire initiation standpoint. Since higher levels of voltage and current than Class 2 are permitted, additional safeguards are specified to provide protection from an electric shock hazard that could be encountered."
(A) Class 1 Power-Limited Circuits. These ircuits shall be supplied from a source that has a rated output of not more than 30 volts and 1000 volt-amperes.
(B) Class 1 Remote-Control and Signaling Circuits.
These circuits shall not exceed 600 volts. The power output of the source shall not be required to be limited.
III. Class 2 and Class 3 Circuits
725.41 Power Sources for Class 2 and Class 3 Circuits.
(A) Power Source. The power source for a Class 2 or a Class 3 circuit shall be as specified in 725.41(A)(1), (2), (3), (4), or (5):
(1) A listed Class 2 or Class 3 transformer
(2) A listed Class 2 or Class 3 power supply
(3) Other listed equipment marked to identify the Class 2 or Class 3 power source Exception: Thermocouples shall not require listing as a
Class 2 power source.
FPN: Examples of other listed equipment are as follows:
(1) A circuit card listed for use as a Class 2 or Class 3 power source where used as part of a listed assembly
(2) A current-limiting impedance, listed for the purpose, or part of a listed product, used in conjunction with a non?power-limited transformer or a stored energy source, for example, storage battery, to limit the output current
(3) A thermocouple
(4) Listed information technology (computer) equipment limited power circuits.
FPN: One way to determine applicable requirements for listing of information technology (computer) equipment is to refer to UL 1950-1995, Standard for Safety of Information Technology Equipment, Including Electrical Business Equipment. Typically such circuits are used to interconnect
information technology equipment for the purpose of exchanging information (data).
(5) A dry cell battery shall be considered an inherently limited Class 2 power source, provided the voltage is 30 volts or less and the capacity is equal to or less than that available from series connected No. 6 carbon zinc cells.
Try reading this as a starter.
From the 2002 NEC:
"Class 1 Circuit. The portion of the wiring system between the load side of the overcurrent device or power-limited supply and the connected equipment. The voltage and power limitations of the source are in accordance with 725.21.
Class 2 Circuit. The portion of the wiring system between the load side of a Class 2 power source and the connected equipment. Due to its power limitations, a Class 2 circuit considers safety from a fire initiation standpoint and provides
acceptable protection from electric shock.
Class 3 Circuit. The portion of the wiring system between the load side of a Class 3 power source and the connected equipment. Due to its power limitations, a Class 3 circuit considers safety from a fire initiation standpoint. Since higher levels of voltage and current than Class 2 are permitted, additional safeguards are specified to provide protection from an electric shock hazard that could be encountered."
(A) Class 1 Power-Limited Circuits. These ircuits shall be supplied from a source that has a rated output of not more than 30 volts and 1000 volt-amperes.
(B) Class 1 Remote-Control and Signaling Circuits.
These circuits shall not exceed 600 volts. The power output of the source shall not be required to be limited.
III. Class 2 and Class 3 Circuits
725.41 Power Sources for Class 2 and Class 3 Circuits.
(A) Power Source. The power source for a Class 2 or a Class 3 circuit shall be as specified in 725.41(A)(1), (2), (3), (4), or (5):
(1) A listed Class 2 or Class 3 transformer
(2) A listed Class 2 or Class 3 power supply
(3) Other listed equipment marked to identify the Class 2 or Class 3 power source Exception: Thermocouples shall not require listing as a
Class 2 power source.
FPN: Examples of other listed equipment are as follows:
(1) A circuit card listed for use as a Class 2 or Class 3 power source where used as part of a listed assembly
(2) A current-limiting impedance, listed for the purpose, or part of a listed product, used in conjunction with a non?power-limited transformer or a stored energy source, for example, storage battery, to limit the output current
(3) A thermocouple
(4) Listed information technology (computer) equipment limited power circuits.
FPN: One way to determine applicable requirements for listing of information technology (computer) equipment is to refer to UL 1950-1995, Standard for Safety of Information Technology Equipment, Including Electrical Business Equipment. Typically such circuits are used to interconnect
information technology equipment for the purpose of exchanging information (data).
(5) A dry cell battery shall be considered an inherently limited Class 2 power source, provided the voltage is 30 volts or less and the capacity is equal to or less than that available from series connected No. 6 carbon zinc cells.
Try reading this as a starter.
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