|
NFPA 70:national electric code 2002edition 725里介绍如下:
3 U: [2 D0 F4 Z6 ]3 E( bClass 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. / _8 c8 S, v( D9 V$ Q
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.
' q8 o& [: W' j7 G' ?0 _. MClass 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.
$ S0 x/ `8 G4 ?9 v* }6 _725.21 class 1circuit classifications and power source requirements.
; y% C. F5 Z- V2 S7 IClass 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).! s: R* M0 N h/ C5 Q
(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.# a o$ P8 T# W* A
(1) class 1 transformers. Transformers used to supply power-limited class 1 circuits shall comply with article 450
8 E# \5 s3 `( P(2) other class 1 power sources.
/ F O# {6 |3 P$ j! q0 t" X: l1 ?. m" o(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 |
|