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NFPA 70:national electric code 2002edition 725里介绍如下:! `9 B$ c# N7 _- f- _9 T6 Q& M
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.
' d0 l. K9 P; Y" R( `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.
# f! o W% n* z$ u# C" W- IClass 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.5 k7 y; m/ F) \3 W1 Y5 L7 P* {
725.21 class 1circuit classifications and power source requirements.
2 ?: _% f, A; b. f# K. w& q' \' WClass 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).
. P' x- C- r3 S( Y(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.2 X* X8 e; p4 P! E2 ~4 v$ m
(1) class 1 transformers. Transformers used to supply power-limited class 1 circuits shall comply with article 450
7 {+ r- ^8 T9 X1 ^. \(2) other class 1 power sources.
. a/ I L5 n! H' D6 r(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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