Mike Dolt Enterprises
Mike Dolt Enterprises
User: antenna2001, Location: 3 Hr 2 Min from Winged Horses
Asked on: Sunday, April 3, 2011 at 8:17 am EDT
Answered on: Tuesday, May 14, 2024 at 3:41 am EDT
Question: In the master electrician exam, there was a question that I was not sure how to answer:What is the minimum size service to supply a dwelling installation consisting of seven 2-wire branch circuits?I took and passed the exam yesterday but this question is bothering me. I don't remember seen a specific section in the NEC that describes, explicitly, how to arrive at the answer.I only had about two minutes to answer so I quickly assumed that all the circuits were 20A for a total of 140A.The multiple answer choices were1. 100A2. 125A3. 150A4. 200AI went for the third answer, 150A.I can not properly justify the answer. I am now reading through Art. 210 and I hope to come up with the correct section numbers to back up the answer. Could someone help me find the right procedure?Thanks
Procedure to Determine Minimum Service Size
1. Determine the Demand Load
Each 2-wire branch circuit is assumed to be 20A (Art. 210.21(B)(1)) Total Demand Load = 7 circuits x 20A/circuit = 140A
2. Apply Demand Factor
For dwelling units, a demand factor of 0.7 is used (Table 220.82) Adjusted Demand Load = 140A x 0.7 = 98A
3. Determine Minimum Service Size
The minimum service size must be not less than the adjusted demand load (Art. 230.42) Rounded up to the next standard size:
100AConclusion
The minimum size service to supply a dwelling installation consisting of seven 2-wire branch circuits is
100A.
Note: The answer choices you provided are incorrect because they are all greater than 100A. The NEC does not explicitly state a formula for this calculation, but the procedure outlined above is based on the relevant sections in the NEC. Flag for review