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NFPA 70:national electric code 2002edition 725里介绍如下:
% w$ t' j I! d8 ]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. " h. b" C% j$ x2 ?5 `
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. . h. s- p! j% m) `' y0 ^ Q
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.
0 y! R/ e2 X8 S/ q725.21 class 1circuit classifications and power source requirements.
6 D! H" s! i P8 V! t- pClass 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).
, k3 D7 z( \. B6 f(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.
4 h+ Q9 H1 r _; q! [1 i3 P& q* @(1) class 1 transformers. Transformers used to supply power-limited class 1 circuits shall comply with article 450
# @. k- {5 g+ ^! q% y(2) other class 1 power sources.
* m1 c; q4 O* | }8 @) G; 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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