It was removed because many inspectors were permitting 36" nipples between enclosures to be supported only by the conduit terminations. This is exactly what the original proposal for the 2008 code would have permitted, but the CMP changed the length from the proposed 36" to 18" when the accepted the proposal.
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8-24a Log #2200 NEC-P08 Final Action: Accept
(342.30(C))
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Submitter: James W. Carpenter, International Association of Electrical
Inspectors
Recommendation: Delete this provision. Also, delete the clause “or permitted to be unsupported in accordance with 342.30(C)” from the last sentence of 342.30.
Substantiation: The concept of a special support rule for short lengths of raceway run between enclosures of various sorts was added to the 2008 NEC for the first time in the history of the NEC with negligible technical substantiation and no evidence of loss experience, and remains at variance from routine trade practice. The existence of a coupling now immediately provokes a support requirement, even on a 6-inch and a 4-inch long heavy-wall 4 trade size steel nipples put together to make an 11-inch (approx.) combined raceway. A 90 degree sweep roughly 2 trade size or larger (any centerline length over 18 in.) now requires intermediate support. The literal text now requires support to structure on a 3-in. nipple if even one of its ends “encounters” a concentric knockout. Although there are those who believe the new rule simply offers limited relief from a rule that required all raceways to be independently supported, routine field experience throughout the history of rigid raceway wiring methods does not substantiate such assertions. We are unaware of any significant attempts to require supports on short nipples. All rigid raceways under NEC rules must be listed, including their couplings; is it conceivable that a coupling between two segments of a short (3 ft or less) nipple so seriously degrades the stability of the raceway that such a support is needed? Concentric knockouts in enclosures are reviewed as part of the UL 50 process, and as anyone working these enclosures recently should be aware, those standards have been strengthened and these knockouts are now more robust than in previous decades; is this the time to require even more support? Raceways generally require support within 3 ft of terminations, and when the entire length is just that long or shorter, no additional support should be needed. In effect, the locknuts and bushings or connectors and locknuts at each end are supports. This is not a new concept for the NEC: CMP 7 just added the wording “(wiring method) fittings shall be permitted as a means of cable support” in a number of cable articles. If carried to its logical conclusion and routinely enforced (however unlikely), this new support rule will likely drive the market in the direction of cabled wiring methods without any technical justification.
It should be remembered that supports to structure are not infallible. Many raceways hang from threaded rod of indefinite length every 10 ft or so and within 3 ft (5 ft. in some cases) of enclosures, depending on the specific rules for the size and character of the supported raceway. Such support clearly meets the rules in this section, but would it add anything to a nipple between enclosures? Further, even when rigid supports such as one-hole clips are used, the raceway beyond the last clip can have an indefinite number of couplings and enter the center knockout of an indefinite number of concentric knockouts; how is this arrangement so inherently more secure than a nipple between enclosures? This new NEC provision was without precedent, and addressed a nonexistent problem.
Panel Meeting Action: Accept
Panel Statement: CMP-8 does not necessarily agree with the submitter’s substantiation. Securement requirements are found in 342.30(A).
Number Eligible to Vote: 12
Ballot Results: Affirmative: 11 Negative: 1
Explanation of Negative:
GRIFFITH, M.: IEEE does not agree with the concluding statement in submitter’s substantiation that “This new NEC provision (in the 2008 NEC)…addressed a non-existent problem.” During the 2008 NEC cycle Panel 8 fully
considered the need for adding the section which the submitter proposes to delete. The Panel determined that the present language was needed to clarify that short nipples do not require additional support and that this was not
universally understood by AHJ’s, especially in remote & rural areas.
Comment on Affirmative:
DABE, J.: The base rule under.30(A) for IMC, RMC, PVC, RTRC, and EMT, remains in force. The conduit systems shall be securely fastened within 3 feet between termination points.
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