Where must an identification plate stating "Service conductor ampacity" be installed?

The requirement for an identification plate stating "Service conductor ampacity" is particularly important when the ampacity of the service conductors is less than that of the overcurrent protection device rated up to 400 amperes. This situation highlights the need for clear communication about the limitations of the service conductors, ensuring that anyone working on or inspecting the system is aware that the conductors may not be able to handle the full capacity that the overcurrent protection might suggest.

When the ampacity is lesser than that of the overcurrent protection, it becomes crucial to indicate this on an identification plate, as it informs electricians, maintenance personnel, and inspectors about the actual capacity of the conductors, potentially preventing overheating and electrical failures. This practice is in line with safety standards and ensures that the electrical system operates efficiently and within safe parameters.

The other options do not accurately reflect the requirement. Services rated over 200 amperes or only in one- or two-family dwellings may not require such a label if the ampacity conforms to regulations. Similarly, placing the identification plate solely for commercial service equipment overlooks the broader applicability of indicating conductor ampacity, which is crucial across different types of electrical systems.