Conduit size in classified area
- Thread starter killer76
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- Mission Viejo, CA
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- Professional Electrical Engineer
Re: Conduit size in classified area
This most likely comes from a misunderstanding of [2005] 501.15(C)(6) or [2002] 501.5(C)(6).
The restriction is on seal fittings not the conduits themselves. Since it was originally introduced in the 1996 NEC, most manufactures now have their seal fitting certified for 40% fill of RMC. In the 2002 NEC it was clarified the fill restriction was based on RMC since other forms of raceways now recognize they may have different internal diameters (I.D.)
Edit: Corrected reference from 1999 NEC to 1996 NEC (I should have remembered - I wrote that Proposal)
[ September 14, 2005, 12:08 PM: Message edited by: rbalex ]
This most likely comes from a misunderstanding of [2005] 501.15(C)(6) or [2002] 501.5(C)(6).
The restriction is on seal fittings not the conduits themselves. Since it was originally introduced in the 1996 NEC, most manufactures now have their seal fitting certified for 40% fill of RMC. In the 2002 NEC it was clarified the fill restriction was based on RMC since other forms of raceways now recognize they may have different internal diameters (I.D.)
Edit: Corrected reference from 1999 NEC to 1996 NEC (I should have remembered - I wrote that Proposal)
[ September 14, 2005, 12:08 PM: Message edited by: rbalex ]
- Location
- Illinois
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- retired electrician
Re: Conduit size in classified area
Bob,
Don
Bob,
I know that is not true of at least one major conduit fitting manufacturer. You have to order a different part number to get a seal fitting suitable for 40% fill. The standard part number is only for 25% fill.
Don
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- Mission Viejo, CA
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- Professional Electrical Engineer
Re: Conduit size in classified area
You're right of course. I should not have given the impression that the seal designs current in 1996 were later certified for 40%.
I should have said most seal manufactures now have lines available that are certified for 40%.
Many of the old 25% designs, can in fact handle 40% fill though as over 25 years of empirical evidence has shown. The issue was created when the NEC dropped the "new work" / "old work" fill distinctions. It took UL over 25 years to recognize it affected seal fittings because there were no documented incidents.
You're right of course. I should not have given the impression that the seal designs current in 1996 were later certified for 40%.
I should have said most seal manufactures now have lines available that are certified for 40%.
Many of the old 25% designs, can in fact handle 40% fill though as over 25 years of empirical evidence has shown. The issue was created when the NEC dropped the "new work" / "old work" fill distinctions. It took UL over 25 years to recognize it affected seal fittings because there were no documented incidents.
- Location
- Illinois
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- retired electrician
Re: Conduit size in classified area
And in some cases all you get with the seal listed for 40% is an oversized seal and a pair of reducing bushings...at a price some what higher than buying the same three parts individually.
Don
And in some cases all you get with the seal listed for 40% is an oversized seal and a pair of reducing bushings...at a price some what higher than buying the same three parts individually.
Don
slipknotbmg
Member
Re: Conduit size in classified area
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"?
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"?
slipknotbmg
Member
Re: Conduit size in classified area
Good point Dillon, If the seal-off is listed for 40% RMC fill, So exceeding that, say 40% fill in a 25% seal-off would not allow you to seal properly per manuf. instructions.
Good point Dillon, If the seal-off is listed for 40% RMC fill, So exceeding that, say 40% fill in a 25% seal-off would not allow you to seal properly per manuf. instructions.
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- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
Re: Conduit size in classified area
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.
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.
Don Gatlin
Member
Re: Conduit size in classified area
I know Crouse Hinds makes an EYSX that is a larger body with the next smaller conduit size threaded.
I know Crouse Hinds makes an EYSX that is a larger body with the next smaller conduit size threaded.
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