At what point must the branch circuit overcurrent device be placed in an electrical system?

The correct placement of the branch circuit overcurrent device is essential for ensuring the safety and proper functioning of an electrical system. The overcurrent device, such as a circuit breaker or fuse, must be located where the conductor receives its supply. This is because it acts as a protective measure, interrupting the flow of electricity if the current exceeds a safe level, thereby preventing potential fire hazards and equipment damage.

Positioning the device at the supply point allows for immediate response to any overcurrent conditions, protecting the entire branch circuit that it serves. This ensures that any fault or overload conditions are addressed before reaching downstream devices and loads, thus enhancing the overall safety of the electrical system.

The other options highlight potential locations for overcurrent devices but do not fulfill the requirement for optimal placement. For example, placing the device before the service head or solely at the panel board may not provide the necessary protection for all circuit branches. Additionally, while the disconnecting means is important for isolating the circuit for maintenance, it does not inherently offer the overcurrent protection needed to safeguard the conductors and connected equipment effectively.