Re: Conduit size in classified area
Originally posted by slipknotbmg:
Wouldn't the conductors passing through the seal be allowed to exceed 40% fill in the seal, being as they are bundled for less than 24"?
Bundling is not the issue here. If it is properly installed, the fiber material that is provided with the sealing compound is ?packed? to insure there is space between the conductors before the compound is poured. Theoretically, this prevents a ?channel? from being formed between three or more conductors that would permit gas to migrate readily through the seal.
In the ?96 general time frame, I did an IEEE paper with a major manufacturer?s Technical and Specifications Compliance Manager. They conducted several 100 tests with 40% fills on their standard line. When installed per manufacturer?s instructions, we didn?t find any combination of conductors that were otherwise legally installed at 40% that failed the standard UL ignition tests. I can?t remember the maximum number of conductors we used, but it was something on the order of 36 THHNs in 1? RMC.
Nevertheless, the UL Standard also calls for specific spacing between the conductors for the tests (though not necessarily for field installation) and this was not always achievable. This required increasing the I.D. of the fitting. Technically it also requires an increase in minimum thickness of the compound per [2002] 501.5(C)(3) for ?25%? fittings greater than 1-1/4? if the installation simply uses an oversized fitting with reducers rather than a ?certified? one.