The overcurrent protection requirements outlined in the NEC can be found in Art. 240, except as noted in Table 240.3. As we noted in Part 16 of our series on Electrical Services, the requirements for overcurrent protection of service equipment are listed in Part VII of Art. 230.
Table 240.3 lists Art. 230 as one of the “other Articles.” It also lists Art. 210 for branch-circuits, but the overcurrent protection requirements for those are in Art. 240. In some cases, another Article changes the overcurrent protection requirements for that application or equipment. A notable example is Art. 430.
The main purpose of Art. 240 is to ensure you protect conductors from being subjected to overcurrent relative to what their ampacity permits. To properly apply Art. 240, you need to understand what overcurrent is and how it differs from overload, short circuit, and fault current.
Overcurrent is any current in excess of the rated current of equipment or the ampacity of a conductor. Any of those three problems (overload, short circuit, fault current) can cause overcurrent. Each of these three problems has variations and each stems from different causes. Good electrical maintenance eliminates many, but not all of the causes. In Part 2, we’ll look at what these three problems are so you get a better understanding of “overcurrent.”
