North American distribution boards are typically housed in sheet metal enclosures, with the circuit breakers 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.
Busbars carry the current from incoming line (hot) conductors to the breakers, which are secured to the bus with either a bolt-on connection (using a threaded screw) or a plug-in connection using a retaining clip. Panelboards are more common in commercial and industrial applications and employ bolt-on breakers. The branch circuit bondingconductors are secured to a terminal block attached directly to the panelboard enclosure, which is itself grounded.
During servicing of the distribution board, when the cover has been removed and the cables are visible, American panelboards commonly have some live parts exposed. In Canadian service entrance panelboards the main switch or circuit breaker is located in a service box, a section of the enclosure separated from the rest of the panelboard, so that when the main switch or breaker is switched off no live parts are exposed when servicing the branch circuits.