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Practice question · NEC Table 220.42
What Is the Demand Load for 40,000 VA of Office Lighting?
Demand-load questions are two steps: the first block at full value, everything after it at the table's percentage. Skip the first block and you land on the trap answer — which the exam plants every single time.
Exam-style question (Sparky QOTD)
An office building has 40,000 VA of general lighting load. Using Table 220.42 demand factors, what is the demand load?
A. 10,000 VA
B. 40,000 VA
C. 14,000 VA
D. 15,950 VA
Answer: D) 15,950 VA. First 3,000 VA at 100%, the remaining 37,000 at 35%.
Where to Find It
Open your Code book to Table 220.42 — and check the column: this is an office building, so use the "other than dwelling" set. The first 3,000 VA is at 100%, and everything after that is at 35%. The math: 3,000 + (37,000 × 0.35) = 3,000 + 12,950 = 15,950 VA.
Why This Works
Demand factors exist because not every light in a big building is on at once. The Code doesn't apply one flat percentage, though — it splits the load into two blocks. The first 3,000 VA stays at full value; only the remainder gets the 35% factor. So: 40,000 − 3,000 = 37,000 VA of "remainder," × 0.35 = 12,950 VA, plus the first 3,000 = 15,950 VA.
That's the whole move. Two blocks, one addition, one multiplication — and it works exactly the same way for every demand-factor question in Article 220. Get the block structure right and the arithmetic is nothing.
Tab Table 220.42 with the note "lighting demand" — it shows up constantly. If your book isn't tabbed yet, our code book tabs guide has this one covered.
The Trap
Option C (14,000 VA) is the trap — it's 40,000 × 0.35 flat, which skips the first 3,000 VA at full value. Every version of this question plants the flat-percentage answer for people who read the table's second row but not its first. Option B (40,000 VA) is the no-demand guess — you apply no factor at all. And option A is just a round number for pure guessers.
Exam Tip
Two habits earn you these points. First, check the column — "other than dwelling" versus dwelling, because this table has both and the stem tells you which building you're in. Second, always handle the first block before multiplying: subtract it, factor the remainder, then add the first block back. Write "first 3k at 100%" on your 220.42 tab and the trap answer stops existing.
Keep Drilling
This is one of 33 NEC topics. Sparky's 1,087 codebook-first questions drill all of them — every question a lookup rep with your book open, 15 minutes a day.