panelboards

Panelboards, also called distribution panels or breaker panels, are electrical distribution devices that house overcurrent protection devices and provide a central point to feed branch circuits from the service equipment. They accept service conductors from the utility or a transfer switch and distribute power to individual circuits while protecting wiring from overload with fuses or circuit breakers.

Construction and configuration: A panelboard consists of an enclosure, bus bars, a set of circuit-breaker spaces, and one or more neutral and grounding bars. They may have a main disconnect (main breaker) or be main-lug only. In residential services, panelboards commonly supply 120/240 V single-phase circuits; commercial/industrial panels may be 208Y/120 V or 277/480 V three-phase. Panels are typically rated by voltage, current (ampere rating), and short-circuit current rating, and must be listed for their intended use.

Types and environments: Main-breaker panels; main-lug panels; subpanels; indoor vs outdoor with appropriate enclosures (NEMA ratings). The choice depends on location, conductor sizing, and required fault-current capabilities. Labels and clearances around the panel are part of proper installation.

Installation and operation: Proper sizing of conductors to panel ampacity, correct breaker types, labeling, and spacing for future circuits are essential. Grounding and bonding are required; neutral conductors and grounding conductors are separated in subpanels. Outdoor panels require weatherproof enclosures and protection against moisture and dust.

Safety and maintenance: Working on panelboards presents arc flash and shock hazards; power must be de-energized during service. Regular maintenance includes verifying tight connections, checking for overheating or corrosion, and ensuring circuits are properly labeled and within design limits.