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NFPA 70:national electric code 2002edition 725里介绍如下:; j5 F, N+ e. [! R
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. , v0 t0 J8 \: z% K& y$ w
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.
; o2 v# o! n. M. B( c( B, p/ Q5 |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.9 i! l" l _+ @9 ~" a9 D
725.21 class 1circuit classifications and power source requirements.8 a3 a+ @3 X% k& ?& m3 ?4 v
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)., A' E; i9 I$ a2 ~5 j5 }
(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.
3 i6 A3 h" v# H! j) m% H, Q% t6 Y9 j(1) class 1 transformers. Transformers used to supply power-limited class 1 circuits shall comply with article 450
/ n$ `2 |9 g. _( y& p(2) other class 1 power sources. + C- u a$ [- d6 F/ Z" }& n
(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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