The guest room lighting load for a motel has already been computed at 60,000 volt-amperes. The applicable demand factors for this occupancy are 50 percent for the first 20,000 volt-amperes, 40 percent for the portion from 20,001 through 100,000 volt-amperes, and 30 percent for anything above that. What is the demand lighting load for the service calculation?
- 26,000 VA
- B60,000 VA
This carries the connected load with no demand factor. Hotels and motels get one of the deepest lighting discounts in the Code precisely because guest rooms are rarely occupied and lit all at once.
- C30,000 VA
This applies 50 percent to the entire load. The 50-percent factor belongs only to the first 20,000 volt-amperes; everything above that moves into a lower bracket.
- D24,000 VA
This applies 40 percent to the entire load. Like the previous error it flattens a bracketed table into a single multiplier, which understates the first slice.
Why A is correct
Bracketed demand factors work like a tax table. The first 20,000 volt-amperes is halved to 10,000, and the remaining 40,000 volt-amperes falls entirely in the 40-percent bracket and becomes 16,000. Adding the two slices gives 26,000 volt-amperes, and the 30-percent bracket never comes into play because the load never exceeds 100,000.
What this question is testing
Tests whether you can apply a multi-tier demand table slice by slice instead of picking one percentage for the whole number, and whether you stop at the correct bracket when the load does not reach the highest tier. It also checks that you recognize the occupancy-specific nature of these factors.
On the job
Hotels, motels, dormitories and any building where the guest rooms do not have permanent cooking provisions get this treatment, and on a large property it can cut the lighting line by more than half. Getting the brackets right matters when the number sits near a service size boundary, because the difference between 800 and 1,000 amperes of switchgear is a six-figure decision. Note that this discount covers the guest room lighting only, not corridors, lobbies, laundry or house loads.
Memory technique
Demand tables stack like tax brackets, slice by slice from the bottom up.
Exam tip
Fill each bracket before you move to the next, and add the slices at the end. Never multiply the total by a single factor.
Where to look it up
Article 220, the lighting load demand factor table. Check the occupancy column carefully, because the dwelling row and the hotel row use different breakpoints and different percentages.