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Thread: pvc conduit separation

  1. #11
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    Quote Originally Posted by jaggedben View Post
    Given that the rule is in a section on adjusting for temperature, I assumed the intent is to prevent transmission of heat from one raceway to another, or build-up of heat if adjacent raceways are both heating. How this section exactly achieves preventing that is a bit beyond me though.

    If that is the case, I would expect some standard for how to know how much that spacing should have to be. Either in inches, or based on the conduit size or OD.

  2. #12
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    May 2011
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    Quote Originally Posted by Cow View Post
    When we have small ditches and a lot of conduits, we'll more often than not cut 12" pieces of 1/2" emt and drive them between the conduits every 10' to maintain separation. For duct banks, we typically use T&B chairs for spacing.
    See, I find this ironic. If the purpose of the rule is to prevent direct heat transfer between raceways then it seems to me that using metal spacers with a low specific heat is going to go a long way towards defeating that purpose. Of course the rule applies equally to multiple metal raceways hung on same piece of metal strut. So whatever. Use metal if you like, it's not against the rule. Again, I'm not defending this rule, just pointing out that it's there.

  3. #13
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    May 2013
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    Quote Originally Posted by jaggedben View Post
    See, I find this ironic. If the purpose of the rule is to prevent direct heat transfer between raceways then it seems to me that using metal spacers with a low specific heat is going to go a long way towards defeating that purpose. Of course the rule applies equally to multiple metal raceways hung on same piece of metal strut. So whatever. Use metal if you like, it's not against the rule. Again, I'm not defending this rule, just pointing out that it's there.

    The spacers aren't continuous, and probably occupy only 5% of the length. 5% = 6 inches per stick, which would be 3" long spacers at two per stick. The majority of the length is spaced by backfill, which would insulate it. Even if metal, the heat transfer path through the metal spacers is not a controlling conductance.

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