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 thelargest 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.
220.60 Noncoincident Loads.
If it is unlikely that two or more noncoincident loads will be in use simultaneously, using only the
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.