Distribution Box Circuit Section Number

North American distribution boards are generally housed in enclosures, with the positioned in two columns operable from the front. Some panelboards are provided with a door covering the breaker switch handles, but all are constructed with a dead front; that is to say the front of the enclosure (whether it has a door or not) prevents the operator of the circuit breakers from contacting live electrical parts within. carry the current from incoming line (hot) conductors to the breakers. [pdf]

Transceiver section of the optical module

TOSA is the component inside the transmit side of SFP ports which is responsible for converting the electrical signal into an optical signal and then transmitting it over the optical fiber strand connected to it. An optical module is a typically hot-pluggable optical transceiver used in high-bandwidth data communications applications. [pdf]