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NFPA 70:national electric code 2002edition 725里介绍如下:1 d0 {9 o5 F2 g N( n, z- o4 I
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. ( P$ v. @9 @$ m4 I
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.
- c. J. S4 f% a5 S% D0 G oClass 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.
. c! G% q/ |$ c, m9 t: U9 P725.21 class 1circuit classifications and power source requirements.* D7 b) ?4 k, o& M* N. y0 b
Class 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).( k; L i8 D0 l
(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.
+ W8 k# z& w I8 g3 q! T0 y# \(1) class 1 transformers. Transformers used to supply power-limited class 1 circuits shall comply with article 450
0 X# \" e. _5 M- H+ x2 n(2) other class 1 power sources.
, q) e. e& c' z0 v( L(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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