Article 240 addresses the actual selection and application of overcurrent protective devices. These requirements are mostly concerned with protection of conductors.

Section 240.4 includes the primary requirements and some special rules dealing with specific cases.

Section 240.4 requires protecting the conductors at their ampacity. This rule establishes a maximum rating of overcurrent device: the ampacity of the conductor. An ampacity must be determined in accordance with Article 310. Section 310.15 (discussed in Conductor Selection & Application) addresses how that is done. This general requirement may be modified, however, by the requirements of Section 240.4, Subsections (A) through (G).

Section 240.4 does not address other types of equipment. These other types of equipment and the applicable code sections are found in Table 240.3, which lists many other articles with specific requirements for overcurrent protection, sometimes including different rules for conductors. Some of these would simply require that the overcurrent device be not less than 125% of the load, which means treating it as if it were a continuous load. Others may provide differing rules based on the specific type of equipment.