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Thread: Cable tray vs. conduits over Class I Division 2 area

  1. #1
    Join Date
    Jun 2018
    Location
    Wisconsin
    Posts
    5

    Cable tray vs. conduits over Class I Division 2 area

    I have an 1,000 amp feeder that needs to go to a building 800 feet away. The feeder will need to be routed outdoors on the roof of several other buildings that are rated Class I Division 2. Due to voltage drop, I believe I'll need (4) sets of 600KCMIL. However, I don't know if I should use a cable tray or conduits. I want to use whatever makes the most sense and is the most economical. If I should use a cable tray, what types of cables should I use and what type of cable tray? Do they need to be suitable for a Class I Division 2 environment as well? I'm assuming the cable tray would need a cover since it's outdoors.

  2. #2
    Join Date
    Apr 2004
    Location
    Mission Viejo, CA
    Posts
    5,238
    It always concerns me a bit when an indoor location is only classified Division 2; it takes a great deal of ventilation to achieve that.

    That said, will the circuits actually be run in or terminate in the classified location?

    Assuming proper classification, the odds are a tray system will be your most cost-effective. You will still need to run the economics.

    If the feeder does interface directly with the classified locations, Sections 501.10(B)(1)(5) generally indicates the acceptable cable Types. Be sure to review their respective Articles in Chapter 3 as well. Also review Article 392 as some tray rated single-conductor cables, which you are likely to use for a 600kcmil installation, are also suitable.

    Article 392 may also affect the sizing of the conductors.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  3. #3
    Join Date
    Mar 2014
    Location
    South Florida
    Posts
    285
    cable tray is going to cost less, but you will need type TC cable.

    building classification is irrelevant if the classified area is physically separated and there is no leakage source (flanges, dampers, exhaust ports, fans) for combustible gases. physically separated means there is a barrier (presumably the roof) between the classified and non-classified space and gas cannot commute from one side to the other under normal conditions.

    i would say, if you were to go tray, use ladder type tray with a cover, to shield the conductors from direct sunlight. although they are resistant to the effects of UV, my preference is for them not be fully exposed because eventually the insulation will dehydrate and begin cracking. less concerned with rain/moisture, unless the insulation begins to fail. you could have a phase to ground fault on the roof of a building housing a classified process

    i personally would go with conduit, stand it off the roof 18 inches, and pull XHHW just so i wouldn't have to worry about it before i retired

    edit: any rodents you have that can get on the roof will also be able to get into the cable tray (safe space shaded in summer and warmer during the winter). they might take a liking to chewing on the insulation.
    Last edited by drktmplr12; 08-01-18 at 05:13 PM.

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