When designing power distribution for a facility, you must assume a lighting load no less than that in Table 220.12 [220.12] if the table specifies your occupancy. Should you use this table for work in an existing facility?
Probably not. The word "general" in Table 220.12's title is a good clue. Are you working with "general" lighting loads that you must calculate by floor space, or do you have a lighting plan designed to support the purpose of the building and the equipment in it?
What if your facility is industrial and thus not listed in Table 220.12? Should you "play it safe" and just select the largest Table 220.12 value? No. Industrial buildings tend to be built for specific purposes, with lighting loads already known. Table 220.12 provides a minimum lighting load value to use where actual lighting loads aren't known.
Use a Table 220.12 "unit load" value only if
- Your facility is one of the specified occupancies.
- You don’t have lighting load data.
If you have lighting load data, don't be surprised if your actual "unit load" (total lighting load divided by total area) greatly exceeds the Table 220.12 value. But if the Table 220.12 value exceeds your calculated value, look for a calculation error and review the lighting design before continuing.