The subpanel is fed by two large hot wires and a neutral wire running through the angled conduit near the top of the panels.
The photograph on the left shows a dual panel configuration: a main panel on the right (with front cover in place) and a subpanel on the left (with cover removed). The incoming bare, stranded ground wire can be seen near the bottom of the neutral bus bar. Three wires (hot black, neutral white, and bare ground) can be seen exiting the left side of the enclosure running directly to a NEMA 5-15 electrical receptacle with a power cord plugged into it. Below the main breaker are the two bus bars carrying the current between the main breaker and the two columns of branch circuit breakers, with each respective circuit's red and black hot wires leading off. The neutral wire is connected to the neutral busbar to the left with all the white wires, and the two hot wires are attached to the main breaker. The three service conductors-two 'hot' lines and one neutral-can be seen coming in at the top.
The photograph to the right shows the interior of a residential service panelboard manufactured by General Electric. 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. The branch circuit bonding conductors are secured to a terminal block attached directly to the panelboard enclosure, which is itself grounded.ĭuring servicing of the distribution board, when the cover has been removed and the cables are visible, American panelboards commonly have some live parts exposed. The neutral conductors are secured to a neutral bus using screw terminals. Residential and light commercial panels are generally referred to as load centers and employ plug-in breakers. Panelboards are more common in commercial and industrial applications and employ bolt-on breakers. 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. 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. North American distribution boards are typically housed in sheet metal enclosures, with the circuit breakers positioned in two columns operable from the front.
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