Sealoff conductor fill
- Thread starter dgs
- Start date
- Status
Pierre C Belarge
Senior Member
- Location
- Westchester County, New York
You would figure the fill of the conduit based on tables 4 & 5 of Chapter 9, then apply it to 25% of the conduit fill as opposed to the standard method.
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
Also remember it is to be 25% of rigid metal conduit (RMC - Art 344) of the same trade size. Section 501.15(C)(6)
What 501.15 (C) (6) states is that the fill of the seal is based on cross-sectional area of a rigid metal conduit of the same trade size. So if you use a 1" seal you would base your 25% fill on 1" rigid fill. You could use listed RB's with a 3/4" conduit if the math works out.
KentAT
Senior Member
- Location
- Northeastern PA
Yes you can, since a 1" regular seal at 25% fill is volume of 0.222 cu. in, and a 3/4" conduit filled to 40% is 0.220 cu in.
Kent
KentAT
Senior Member
- Location
- Northeastern PA
oops, should be square inches...
- Location
- Illinois
- Occupation
- retired electrician
When this rule fist came out, some manufactures would send you the next larger size seal with two reducing bushings and charge you about 50% more than if you bought the 3 pieces individually:grin:. Now they just tap smaller threads into the ends of the larger seal...and still charge more than if you buy the larger seal and the reducing bushings.
6) Conductor Fill. The cross-sectional area of the conductors permitted in a seal shall not exceed 25 percent of the cross-sectional area of a rigid metal conduit of the same trade size unless it is specifically identified for a higher percentage of fill.
I have no arguement with the fact that a larger seal with RBs meets the 25% requirement. To me the "specifically identified " portion means you need to use an EYSX type seal. Wrong thinking?
I have no arguement with the fact that a larger seal with RBs meets the 25% requirement. To me the "specifically identified " portion means you need to use an EYSX type seal. Wrong thinking?
If the seal is specifically identified for a higher fill you could fill the seal up to the listing capacity which may be over 25%. Or you could use RBs on a larger seal. 501.15 (C) (6) just states that unless the seal is identified for a higher fill 25% is the max. It doesn't require a EYSX seal it just gives you the choice.
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
I?m claiming paternity here.
When UL announced some 25 years after the fact that seal fittings were only tested for 25% fill, it was my idea to permit ?listed explosionproof reducers? at the seal or use ?specifically identified? seals for over 25%. I was a member of API?s Committee on Refinery Installations (CRI), Subcommittee on Electrical Equipment (SOEE) and the RP-500/NEC/NFPA Working Group at the time and sold the idea to them. The SOEE submitted it to the API, Electrical Interdepartmental Advisory Group (IAG), the ?official? API body for such things. The IAG Chair is automatically the API rep on CMP14. The IAG made the formal Proposal to NFPA.
The ?rigid metal? was submitted in my own name in the next Code cycle.
It is critical here to recognize the difference between ?listed? and ?identified.? They are not synonymous.
All seals must be listed: 501.15(C)(1). The seals mentioned in 501.15(C)(6) are listed. But ?standard? seals are limited to no more than 25% fill of RMC of the same trade size. As pointed out by others, this is a cross-section calculation.
Any seal may be ?identified,? i.e., ?[r]ecognizable as suitable for the specific purpose, function, use, environment, application, and so forth, where described in a particular Code requirement;? in this case, being suitable to seal conductors with a cross section that doesn?t exceed 25% of the cross section of an RMC of the same trade size.
One way is to simply determine that the conductors don?t exceed 25% of an RMC of the same trade size from the Tables.
Another is to know, that they don?t exceed 25% of a larger trade size and slip in a reducer to match them up. Here the only problem was potential boundary issues - that was solved simply by CMP14 saying it was OK. (Actually, at least two manufacturers were also SOEE members and they confirmed there was no significant gas migration for virtually any reasonable range of reducers.)
Finally, a responsible third party can certify that a seal has a cross section suitable for ANY specific percentage of an associated trade size. It doesn?t even have to be 40% - it could even be something bazaar like 63.8%. (Of course their reputation for being responsible would quickly be called into question; but then, it already had been for not letting anyone know about the 25% limitation for over 25 years.)
At that point, the actual raceway it is connected to is irrelevant as far as the seal is concerned. As far as the overall installation is concerned though, the raceway?s fill can?t exceed the percentage shown in Chapter 9, Table 1. If the seal fitting and raceway just happen to be the same trade size, all is well with the world. If not, there are other reasonable means. (Including, as one manufacture did, showing 40% fill in a ?standard? seal was no big deal ? heck, we?d already been doing it for 25 years; it just isn?t in the Code.) :grin:
When UL announced some 25 years after the fact that seal fittings were only tested for 25% fill, it was my idea to permit ?listed explosionproof reducers? at the seal or use ?specifically identified? seals for over 25%. I was a member of API?s Committee on Refinery Installations (CRI), Subcommittee on Electrical Equipment (SOEE) and the RP-500/NEC/NFPA Working Group at the time and sold the idea to them. The SOEE submitted it to the API, Electrical Interdepartmental Advisory Group (IAG), the ?official? API body for such things. The IAG Chair is automatically the API rep on CMP14. The IAG made the formal Proposal to NFPA.
The ?rigid metal? was submitted in my own name in the next Code cycle.
It is critical here to recognize the difference between ?listed? and ?identified.? They are not synonymous.
All seals must be listed: 501.15(C)(1). The seals mentioned in 501.15(C)(6) are listed. But ?standard? seals are limited to no more than 25% fill of RMC of the same trade size. As pointed out by others, this is a cross-section calculation.
Any seal may be ?identified,? i.e., ?[r]ecognizable as suitable for the specific purpose, function, use, environment, application, and so forth, where described in a particular Code requirement;? in this case, being suitable to seal conductors with a cross section that doesn?t exceed 25% of the cross section of an RMC of the same trade size.
One way is to simply determine that the conductors don?t exceed 25% of an RMC of the same trade size from the Tables.
Another is to know, that they don?t exceed 25% of a larger trade size and slip in a reducer to match them up. Here the only problem was potential boundary issues - that was solved simply by CMP14 saying it was OK. (Actually, at least two manufacturers were also SOEE members and they confirmed there was no significant gas migration for virtually any reasonable range of reducers.)
Finally, a responsible third party can certify that a seal has a cross section suitable for ANY specific percentage of an associated trade size. It doesn?t even have to be 40% - it could even be something bazaar like 63.8%. (Of course their reputation for being responsible would quickly be called into question; but then, it already had been for not letting anyone know about the 25% limitation for over 25 years.)
At that point, the actual raceway it is connected to is irrelevant as far as the seal is concerned. As far as the overall installation is concerned though, the raceway?s fill can?t exceed the percentage shown in Chapter 9, Table 1. If the seal fitting and raceway just happen to be the same trade size, all is well with the world. If not, there are other reasonable means. (Including, as one manufacture did, showing 40% fill in a ?standard? seal was no big deal ? heck, we?d already been doing it for 25 years; it just isn?t in the Code.) :grin:
jeremysterling
Senior Member
- Location
- Austin, TX
And a lovely child it is, Bob
Thank you very much for the very informative answer. Nothing like being able to go right to the source for the answer.I have a feeling that we are still going to specify the extended series of seals if only for the convenience, but it's nice to know that a bigger size with RBs can be used in case of emergency and not compromise the installation's legality.
I've only been doing hazardous location design for 5+ years now and still feel like a newbie, so it's a real help to be able to here for a great knowledge base.
- Status