Article 220 prescribes requirements for feeder and service load calculations in Part III. In Part IV, Art. 220 provides an optional method of performing these calculations. Actually, Part IV provides several optional methods depending on whether the occupancy is residential (any of three variations), a school, existing, or a restaurant.
If you've already learned the standard method, why bother with the optional method? How do you know when the optional method is permissible? The answer to both questions is that if you have the information required for the simpler optional method in Part IV, you'll save time using it.
The standard method accounts for certain unknown information by requiring additional calculation. But if you actually have this information, you can use the optional method and do less calculation. For particular kinds of construction, notably apartment buildings, the information is often known and you can use the optional method.
If you're not sure that you have the required information, you can begin with the optional method. If you run into something it calls for but don't have the information, you can change to the standard method. This is more efficient than it sounds. You can make a checklist for quick assessment.
In our next issue, we'll look at what would be on that checklist.