|
NFPA 70:national electric code 2002edition 725里介绍如下:
9 O2 a. B r7 f/ X0 ]) F+ D$ o4 pClass 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.
. a. a- A; ?5 B; |6 W% `2 j1 J5 SClass 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. ( B, q! J' G' B
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.
. M/ \. R5 B/ D. U1 |/ ~7 j725.21 class 1circuit classifications and power source requirements.
, W' e& F# K* h. X, v6 bClass 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).( N$ m9 j5 k+ ?: O( T- W! J
(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.8 O, e7 ~" d- P% S6 U n) w( p
(1) class 1 transformers. Transformers used to supply power-limited class 1 circuits shall comply with article 450
. G3 J3 |& [. t1 C(2) other class 1 power sources.
3 B: E t( D7 ^, S: e7 @7 m" G5 s(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 |
|