2-166 Log #1319 NEC-P02 Final Action: Accept in Principle
(210.19(A)(1))
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TCC Action: The Technical Correlating Committee understands that the Panel Action on this Proposal is to identify the existing Exception as “Exception No. 1” and the Exception being added as “Exception No. 2” to be located immediately following the existing Exception.
Submitter: Mike Holt, Mike Holt Enterprises
Recommendation: Revise as follows:
210.19 Conductors – Minimum Ampacity and Size.
(A) Branch Circuits Not More Than 600 Volts.
(1) General. Branch-circuit conductors shall have an ampacity not less than the maximum load to be served. Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the minimum branch-circuit conductor size, Branch-circuit conductors that are connected to an overcurrent device assembly shall have a minimum allowable ampacity, before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.
Substantiation:
“Minimum Rating and Size”: The identical wording should be used for 210.19, 215.2, and 230.42. Confusion reigns as to under what conditions grounded conductors are subject to the same 125 percent of continuous load sizing requirements as are ungrounded conductors. During the 2005 Code cycle this issue was addressed for feeders, but action was deferred. ROC No. 2-145 included a lucid, sound “substantiation” that unfortunately was rejected by CMP 2 at that time. Now is an excellent time to re-evaluate that “substantiation” and adopt its intent.
The basis for the 125 percent requirement stems from the manner in which listed overcurrent devices are tested. During continuous load tests of enclosed overcurrent devices, in order to prevent nuisance tripping, it has been found that it is necessary to limit the current to 80 percent of the device’s rating. Conductors are sized, then, (1) at 125 percent of the continuous current in accordance with the allowable ampacity determined from Table 310.16, and (2) per the terminal temperature limitations of 110.14(C).
The reality is that the enclosed overcurrent devices rely on the mass of the conductors to act as heat sinks that dissipate excess thermal energy and thereby avoid unacceptable nuisance tripping. Of course, since overcurrent devices cannot distinguish between ungrounded and grounded conductors, in both cases the conductor sizes must be based on calculations that include an additional 25 percent factor when the load is continuous. On the other hand, there is no reason to add 25 percent to the load of a conductor that is not connected to a device that is not subject to nuisance tripping, such as in the case of a grounded conductor connected a neutral terminal bus.
The end result of this proposal is twofold:
1. The additional 25 percent continuous load requirement applies only to conductors, both ungrounded and grounded, that connect to an overcurrent device (unless, of course, the assembly is listed for operation at 100 percent of
its rating).
2. Grounded conductors that carry continuous loads and that connect only to neutral buses, or to devices not subject to nuisance tripping, are not required to have their loads increased by 25 percent.
This proposal accomplishes that goal and, in hand with similar proposals made in two other Articles, brings into conformity the requirements for branch circuits (210.19), feeders (215.2), and services (230.42).
Panel Meeting Action: Accept in Principle
Add a new exception to 210.19(A)(1) to read:
Exception: Grounded conductors that are not connected to an overcurrent device shall be permitted to be sized at 100% of the continuous and noncontinuous load.
Panel Statement: The panel has accepted the submitter’s concept, but has added the provision as an exception to the main rule. The concern with the submitter’s proposed language is that it may be interpreted that the conductors
have to terminate directly to an overcurrent device.
Number Eligible to Vote: 12
Ballot Results: Affirmative: 12
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