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NFPA 70:national electric code 2002edition 725里介绍如下:
/ F1 f: f' U* a. WClass 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. & w- z# |8 N( `! O8 b
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.
/ e% l' n7 R5 g9 G: t; YClass 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 for Class 2 are permitted, additional safeguards are specified to provide protection from an electric shock hazard that could be encountered.
6 M3 h" P0 Z% E9 _ g8 n! d725.21 class 1circuit classifications and power source requirements.
8 P1 _4 {2 q4 m) iClass 1 circuits shall be classified as either class 1 power-limited circuits where they comply with the power limitations of 725.21(A) or as class 1 remote-control and signaling circuits where they are used for remote control or signaling purposes and comply with the power limitations of 725.21(B).
4 @- r' f( y& n# f$ @! U, b. o(A) class 1 power-limited circuits. These circuits shall be supplied from a source that has a rated output of not more than 30 volts and 1000 volt-amperes., n4 h: X4 U9 |2 B
(1) class 1 transformers. Transformers used to supply power-limited class 1 circuits shall comply with article 450
+ i. ? v. v: K* q+ R(2) other class 1 power sources. / v0 `' Y8 [( {% \/ ^6 f
(B) Cass 1 remote-control and signaling circuits. These circuits shall not exceed 600volts the power output of the source shall not be required to be limited |
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