NEC Example D1b

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He is referring to the following example from Annex D:

Example D1(a) One-Family Dwelling
The dwelling has a floor area of 1500 ft2, exclusive of an unfinished cellar
not adaptable for future use, unfinished attic, and open porches. Appliances
are a 12-kW range and a 5.5-kW, 240-V dryer. Assume range and
dryer kW ratings equivalent to kVA ratings in accordance with 220.54 and
220.55.

...detailed calcs follow with results used in example b


Example D1(b) One-Family Dwelling
Assume same conditions as Example No. D1(a), plus addition of one 6-A,
230-V, room air-conditioning unit and one 12-A, 115-V, room airconditioning
unit,* one 8-A, 115-V, rated waste disposer, and one 10-A,
120-V, rated dishwasher. See Article 430 for general motors and Article
440, Part VII, for air-conditioning equipment. Motors have nameplate
ratings of 115 V and 230 V for use on 120-V and 240-V nominal voltage
systems.
*(For feeder neutral, use larger of the two appliances for unbalance.)
From Example D1(a), feeder current is 78 A (3-wire, 240 V).

Line A, Neutral, Line B
Amperes from Example D1(a) = 78, 61, 78
One 230-V air conditioner = 6, —, 6
One 115-V air conditioner and 120-V dishwasher = 12, 12, 10
One 115-V disposer = —, 8, 8
25% of largest motor (see 430.24) = 3, 3, 2
Total amperes per line = 99, 84, 104

Therefore, the service would be rated 110 A.


es1451
The example has already detailed the calculations. What specifically are you having trouble with?
 
Example D1b

Example D1b

Thanks for your help. I need to understand the 25% of the largest motor on line B. On line A it is 3A,the neutral load is 3A which is 25% of 12A. Explain the calculation of line B which is 2A.
 
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