NEC Quiz: Article 220, Part Two Answers

by Mark Lamendola

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1.   [220.16]. Three. There are two methods for dwelling units. One is for loads for structural additions or a previously unwired portion of an existing dwelling unit—either of which exceeds 500 square feet. The second method for dwelling units applies to new or extended circuits in previously wired dwelling units. The third method applies to loads for new or extended circuits in structures other than dwelling units.

2.      [220.18]. None. The total load shall not exceed the rating of the branch circuit.

3.      Article 430. This is the largest Article in the NEC, so be sure you use Figure 430.1 so you can approach it efficiently and avoid mistakes.

4.      Article 440. Because air conditioners are essentially refrigeration loads, Article 440 applies to them as well.

5.      [220.19(B). Contrary to what some people think, you do not use the lamp wattage. You use the total amperage rating of the fixture, so you can account for the current draw of the ballasts, transformers, and any other components. This applies to all types of inductive lighting, such as metal halide and low pressure sodium, not just fluorescent.

6.      [220.40]. Yes. There are two principles, here. One is load diversity (also referred to as “nonincident loads”—see 220.60. For example, you do not run your heat and your air conditioning at the same time, so you use only the larger of the two loads for your calculations. The other is demand factor. Article 220 contains half a dozen demand factor tables. But you may also get an engineering exception granted by the AHJ. For example, you may have 8 welding receptacles in a shop but there is realistically space for only two welders at a time. The AHJ is not bound to grant any exceptions, and may require additional controls for the exceptions to be granted. The best time to apply for exceptions is immediately after construction drawings are stamped and before construction begins.

7.      [220.42] They apply to the portion of the total branch-circuit load calculated for general illumination. They do not apply to determining how many branch circuits to have.

8.      [220.52]. 1500VA. You can include these loads with the general lighting load and apply the demand factors provided in Table 220.42.

9.      You use the more restrictive Table 220.54, rather than Table 220.56.

10.  There are two. The first is where the wiring system is a 3-wire circuit consisting of 2-phase (yes, that’s hyphenated) wires and the neutral of a 4-wire wye system (3 phases and a neutral). The second is where you have non-linear loads supplied from a 4-wire wye system. In either case, the purpose is to prevent burning up the neutral. Annex D is one of the best features of the NEC, yet few people spend any time reading it. The examples there help you understand neutral sizing as it should be understood.