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NFPA 70:national electric code 2002edition 725里介绍如下:$ U: b* X+ f8 `
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. , C; R. g3 v7 n2 p5 O k, `: L
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. 5 H6 Z9 O' f! L1 [+ ?
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 for Class 2 are permitted, additional safeguards are specified to provide protection from an electric shock hazard that could be encountered.
6 D: c! c/ O) e6 H" f725.21 class 1circuit classifications and power source requirements.
8 G: z4 X( v3 s' C* vClass 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).
1 u) P8 A2 }+ c4 r" r(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.
: X/ U( E6 ~! \/ s3 W a9 [" v(1) class 1 transformers. Transformers used to supply power-limited class 1 circuits shall comply with article 4506 p. e" m3 v/ j( J5 O
(2) other class 1 power sources. ( I" q0 Z1 u6 Z/ w: a5 w( t8 @8 v7 y
(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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