Fuse box

A distribution board (also known as panelboard, breaker panel, or electric panel) is a component of an electricity supply system that divides an electrical power feed into subsidiary circuits, while providing a protective fuse or circuit breaker for each circuit in a common enclosure. Normally, a main switch, and in recent boards, one or more residual-current devices (RCD) or residual current breakers with overcurrent protection (RCBO), are also incorporated.

In the United Kingdom, a distribution board designed for domestic installations is known as a consumer unit.

In a North American distribution board, the circuit breakers are generally positioned in two columns. Circuit breaker panelboards are always dead front, that is, the operator of the circuit breakers is unable to contact live electrical parts. During servicing of the distribution board itself, though, when the cover has been removed and the cables are visible, North American breaker panelboards commonly have some live parts exposed.

Breakers are usually arranged in two columns. In a U.S.-style board, breaker positions are numbered left-to-right, along each row from top to bottom. This numbering system is universal with numerous competitive manufacturers of breaker panels.

Each row is fed from a different phase (A, B, and C below), to allow 2- or 3-pole common-trip breakers to have one pole on each phase. In North America, it is common to wire large permanently installed equipment line-to-line. This takes two slots in the panel (two-pole) and gives a voltage of 240 V for split-phase electric power, or 208 V for three-phase power.

The picture to the right shows the interior of a standard residential service, North American General Electric style breaker panel. The three power wires - two hot and one neutral - can be seen coming in at the top. The neutral wire is connected to the neutral busbar to the left with all the white wires, and the other two are the hot wires attached to the main breaker. Below it are the two rows of circuit breakers with the circuits' red and black hot wires leading off. Three wires (hot black, neutral white, and bare ground) can be seen directly exiting the box and running to a NEMA 5-15 electrical receptacle with a power cord plugged into it. The incoming bare stranded ground wire can be seen near the bottom of the neutral bus bar.

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Wikipedia