PI: 220.60 Noncoincident Loads

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
Here's a PI I just submitted. Cheers, Wayne

220.60 Noncoincident Loads.
If it is unlikely that two or more noncoincident loads will be in use simultaneously, using only the largest load(s) that will be used at one time for calculating the total single load that results in the largest total load of a feeder or service shall be permitted. If a motor or air-conditioning load is part of the noncoincident load and is not the largest of the noncoincident loads, 125 percent of either the motor load or air-conditioning load, whichever is larger, shall be used in the calculation.

Statement of Problem and Substantiation for Public Input

The 2020 and 2023 NEC revisions to this section have added language to cover some of the corner cases with noncoincident loads and load calculations, but the result has not been entirely clear, nor comprehensive. The proposed revision seeks to be both clearer and comprehensive.

If a feeder (or service) supplies two (or more) non-coincident loads A and B, then the load calculation procedure should simply be split: first consider only load A to be present and calculate the total feeder load. Then consider only load B to be present and calculate the total feeder load. Use whichever result is larger.

So that is what the proposed revision says to do. This already covers all combinations of motors loads whether they be the nominal larger or smaller of the noncoincident loads. Indeed, the following pair of examples shows that which of the two loads should be in the final answer can not be determined just by looking at the noncoincident loads in isolation, but only by considering the other feeder loads as well:

Example 1: a feeder supplies only two noncoincident loads, either (A) a 110A non-continuous, non-motor load, or (B) a 100A FLC motor load. For case A, the load is 110A. For case B, the load is 125% * 100A = 125A. Case B controls.

Example 2: in addition to the noncoincident loads A and B in Example 1, the feeder also supplies a 120A FLC motor load. Then for case A, the load is 125% * 120A + 110A = 260A. While for case B, the load is 125% * 120A + 100A = 250A. Now case A controls.

Therefore it is necessary that 220.60 include language that compares the total load for each case, rather than just comparing the individual non-coincident loads.
 

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
Looks like this got grouped with other proposals and made it to the next round:

TG 4, FR 14
Committee Statement: Section 220.60 has
been rewritten and restructured to clarify
the determination and treatment of
noncoincident loads.
Requirements regarding the “125 percent of
either the motor load or air‐conditioning
load, whichever is larger” was originally
added to clarify that the value included
application of the motor‐operated and
combination loads as specified in 220.11(A)
(Refer to FR 8062‐NFPA 70‐2018; note that
220.11(A) was 220.18(A) in the 2020 NEC).
Present wording is confusing, so rather than
restate the requirement, the statement is
revised to note that the largest
noncoincident load treat the motor‐
operated and combination loads as specified
in 220.11(A), thus maintaining the original
intent of the requirement.
List items were added to specify what is
considered as noncoincident loads, with
feeders and services maintaining the
traditional usage of “two or more loads that
are unlikely to be in use simultaneously”,
and a more rigorous requirement applying
to branch‐circuits, since those loads do not
benefit from diversity of multiple loads.
Section 220.60 is also relocated to Article
220, Part I (General), to allow the provision
to apply to load calculation throughout
Article 220, including branch‐circuits in
addition to feeders and services.
 
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