Final answer:
An overcurrent device like a fuse or circuit breaker is required to protect a power limited fire protective signaling circuit, and it should be rated at the largest size necessary to prevent overheating due to excessive current.
Step-by-step explanation:
A power limited fire protective signaling circuit must be protected by an overcurrent device rated at the largest size necessary to prevent excessive heating and potential fire hazards due to an overloaded current. The overcurrent device, such as a fuse or circuit breaker, should be selected based on the current carrying capacity of the wires in the circuit, as well as the transformer output supplying the circuit. The power dissipated in the supply wires can be calculated using the formula P = I²Rw, where P is the power, I is the current, and Rw is the resistance of the wires. If the actual resistance or the current exceeds safe limits, the power dissipated will increase, resulting in overheating, which can be a serious thermal hazard. As such, fuses and circuit breakers are critical safety devices that help prevent electrical fires by interrupting the flow of electricity when the current exceeds a predetermined safe level.