Cooking Equipment Calculations, Part III

220.19 Electric Ranges and Other Cooking Appliances

Article 220 of the National Electrical Code contains specifications for calculating branch-circuit, feeder and service loads. Part I, titled General, contains general requirements and specifications for computing branch-circuit loads. The branch-circuit loads are combined with other applicable demand factors in Parts II, III or IV to determine feeder and/or service loads. Some requirements in Part II are only applicable in nondwelling occupancies.

For example, receptacle loads in other than dwelling units must be calculated in accordance with 220.13. Some requirements only apply to dwellings units. For example, requirements in 220.16, 17 and 18 are applicable in dwelling units only. Demand loads in 220.19 apply to dwelling units unless meeting the stipulations in the fifth note to Table 220.19. Section 220.19 and Table 220.19 pertain to household electric ranges and other cooking appliances individually rated in excess of 1 3/4kW. Last month’s In Focus continued discussing provisions for calculating household cooking equipment. This month, the discussion continues with a detailed explanation of cooking equipment demand factors.

Up to this point, each household cooking appliance has been rated 12kW or less. Ranges over 12kW through 27kW must be calculated in accordance with either the first or second note under Table 220.19. When all the ranges are rated the same, use the first note. When they are not rated the same, use the second note. The demand loads in Column C are only applicable if the appliances are rated 12kW or less. For ranges individually rated more than 12kW, but not more than 27kW, the maximum demand in Column C must be increased 5 percent for each additional kilowatt of rating (or major fraction thereof) by which the rating of individual ranges exceeds 12kW (Note 1 under Table 220.19).

Note 1 applies if each range has the same kilowatt rating. The demand loads in Column C, whether one or more ranges, must be increased when the individual ranges are rated more than 12kW. The amount of increase is only 5 percent for each additional kilowatt over 12kW. After finding the demand load in Column C, increase that demand by the appropriate percentage. For example, what is the service demand load for one 14kW range? First, find the percentage by which Column C must be increased. A 14kW range exceeds 12kW by 2kW (14 - 12 = 2). Since Column C must be increased 5 percent for each additional kilowatt of rating above 12, the maximum demand listed in Column C for one range must be increased by 10 percent (2 x 5 = 10). The increased amount is 0.8kW (8 x .10 = 0.8). This increased amount must be added to the original demand load (8 + 0.8 = 8.8). The service demand load for one 14kW range is 8.8kW (See Figure 1).

Regardless of the number, the first note applies if all the ranges are rated the same and are more than 12kW. For example, what is the demand load for 15 15kW ranges? A 15kW range exceeds 12kW by 3kW (15 - 12 = 3). The demand in Column C must be increased by 15 percent (3 x 5 = 15). Note: Do not increase the number of ranges by 15 percent. The increase applies to the maximum demand in Column C. The demand load for 15 ranges is 30kW. The increased amount is 4.5kW (30 x .15 = 4.5). Add the increased amount to the original demand (30 + 4.5 = 34.5). The demand load for fifteen 15kW ranges is 34.5kW (See Figure 2).

When applying note 1, the range ratings (before applying Column C) cannot include a fraction of a kilowatt. The fraction must either be dropped, or rounded up to the next whole kilowatt rating. When the fraction is less than .5, drop the fraction. For example, what is the service demand load for one 13.4kW range? Since the .4 is not a major fraction, drop the .4 and find the demand for one 13kW range. A 13kW range exceeds 12kW by 1kW (13 - 12 = 1). The demand in Column C must be increased by 5 percent (1 x 5 = 5). The increased amount is 0.4kW (8 x .05 = 0.4). Add the increased amount to the original demand (8 + 0.4 = 8.4). The service demand load for one 13.4kW range is 8.4kW (See Figure 3).

Round the kilowatt rating up to the next whole number when the kilowatt rating contains a fraction of .5 or more. For example, what is the service demand load for one 15.5kW range? Since the .5 is a major fraction, round the 15.5 up to a 16kW range and find the demand load. A 16kW range exceeds 12kW by 4kW (16 - 12 = 4). The demand in Column C must be increased by 20 percent (4 x .05 = .20). The increased amount is 1.6kW (8 x .20 = 1.6). Add the increased amount to the original demand (8 + 1.6 = 9.6). The service demand load for one 15.5kW range is 9.6kW (See Figure 4).

Apply this same principal to multiple ranges all of the same rating. For example, what is the service demand load for 40 13.6kW ranges? Since the .6 is a major fraction, round the 13.6 up to 14kW and find the demand. A 14kW range exceeds 12kW by 2kW (14 - 12 = 2). Since Column C must be increased 5 percent for each additional kilowatt of rating above 12, the maximum demand in Column C for 40 ranges must be increased by 10 percent (2 x .05 = .10). The total number of ranges is 40. Where the number of appliances is from 26 to 40, add 15 to the number of appliances and the sum is the kilowatt demand load. Fifteen added to 40 appliances is 55 (15 + 40 = 55). If the ranges were 12kW each, the demand load would be 55kW. Since the ranges are rated more than 12kW, the demand must be increased. The increased amount is 5.5kW (55 x .10 = 5.5). This increased amount must be added to the Column C demand load (55 + 5.5 = 60.5). The service demand load for 40 13.6kW ranges is 60.5kW (See Figure 5).

The first note under Table 220.19 applies to ranges over 12kW through 27kW, but this could be a little misleading. As previously mentioned, when the range rating contains a fraction of a kilowatt, it must either be dropped or rounded up. Fractions lower than 12.5kW are dropped, and therefore the first note does not apply. For example, what is the service demand load for 20 12.4kW ranges? Since the .4 is not a major fraction, drop the .4 and find the demand load. The demand in Column C for 20 12.4kW ranges is 35kW. Therefore, the first note under Table 220.19 actually applies to ranges 12.5kW through 27kW.

Next month’s In Focus continues the discussion of household cooking equipment computations in 220.19. EC

MILLER, owner of Lighthouse Educational Services, teaches classes and seminars on the electrical industry. He is the author of “Illustrated Guide to the National Electrical Code” and NFPA’s “Electrical Reference.” He can be reached at 615.333-3336, charles@charlesRmiller.com or www.charlesRmiller.com.