The pass rate for electrical exams is low, even though the exams are open book. Yet among people who prepare by using any of the leading exam prep systems, the pass rate is high. Some of the performance improvement is due to solving practice problems, but mostly it’s due to understanding the “where and why” of the NEC schema—how the NEC organizes the calculation requirements.
The exams, just like real-world electrical work, test your understanding of the NEC’s schema. The exams have a time limit, so you can’t spend all day poking around in the NEC until you find the relevant requirements. When you’re charging billable hours, you can’t do that in real life either.
But why doesn’t the NEC have calculation process flow charts, worksheets, or step by step instructions? One reason the NEC doesn’t have all this additional (and costly) material is the scope of the NEC. It’s not an instruction manual for untrained persons [90.1(C)]. Nor is it a design specification. Expanding the NEC’s scope to include either of these two purposes would vastly increase its size and complexity.
Nor is the NEC concerned with optimal design. Instead, the NEC provides the minimum requirements to safeguard people and property. Per the NEC, you might select a 4AWG conductor for a given circuit. But you might want a larger conductor to accommodate future loads. Or perhaps it’s a long run and you have efficiency concerns (the NEC does not have a voltage drop requirement).