A combination device whose primary function is fault detection and circuit interruption is generally classified as protection apparatus rather than as a plug or socket. The essential character analysis focuses on whether the protective function or the connection function predominates. Given the dual-function nature of these products, a CBP binding ruling provides the most reliable classification outcome.

Automatic circuit breakers respond to overcurrent conditions through a defined trip mechanism and are specifically enumerated in heading 77252. Apparatus classified under 77253 NES includes devices that protect circuits through other means — such as ground-fault sensing, arc detection, or voltage monitoring — that do not operate as conventional circuit breakers. The functional distinction, supported by technical documentation, is the key to correct classification.