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Why CL 1 circuits required to be 600 V rated

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deanmk

Member
Why are Class 1 circuits required to have 600 Volt insulation? I?m looking for a reason not a code reference. What?s the thinking behind this requirement?

725.25 reads Class 1 wiring shall be installed in accordance with part 1 of Article 300.
725.26 (B)(1) allows class 1 circuits to be installed with Article 300 wiring.
725.25(B) requires the conductor insulation to be rated 600 V.
But Article 300.3 (C)(1) would allow a 120 Volt circuit to have a 300 V insulation.

Therefore why not allow Class 1 circuit under the same constraints to have 300 V insulation.
 
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jbwhite

Senior Member
Re: Why CL 1 circuits required to be 600 V rated

This is from the 2005 code:
725.26 Conductors of Different Circuits in the Same
Cable, Cable Tray, Enclosure, or Raceway. Class 1 circuits
shall be permitted to be installed with other circuits as
specified in 725.26(A) and 725.26(B).
(A) Two or More Class 1 Circuits. Class 1 circuits shall be
permitted to occupy the same cable, cable tray, enclosure, or
raceway without regard to whether the individual circuits are
alternating current or direct current, provided all conductors
are insulated for the maximum voltage of any conductor in the
cable, cable tray, enclosure, or raceway.
 
D

deanmk

Member
Re: Why CL 1 circuits required to be 600 V rated

jbwhite has a good point. If 725.27 (B) mandates all conductors to have 600 V rating (that?s how I read "shall be suitable") then what the heck does 725.26(A) mean? Maybe 725.26(A) is referring to the "other conductor" not the CL 1 conductors, although it does say "all" conductors. Originally I was confused with 300.3(C) now I'm doubly confused.
 
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