Panelboards

Summary

Panelboards are cabinets mounted in or on walls, with a bus and breakers or fused switches that feed branch circuits and smaller feeders; residential versions are called load centers. Panel locations, sizes, and spare capacity affect wall depth, closet and corridor space, and working clearances, and they must be kept accessible and out of storage rooms and bathrooms.

Cols

Image

Load center: residential panelboard with plug-on breakers
Lighting and appliance panel / power panel: commercial panel types
Main breaker / main lug only (MLO): panel with or without its own main device
Flush / surface mounted: recessed in the wall or mounted on its face
Spaces / poles: breaker positions; single-pole 120 V, two-pole and three-pole circuits
Panel schedule: circuit directory and load summary
AFCI / GFCI breakers: arc-fault and ground-fault protective breakers
Smart panel: panel with circuit-level monitoring and load control

Standards

Ratings

Common commercial ratings 100 to 400 A at 208Y/120 V or 480Y/277 V; residential 100 to 200 A at 120/240 V
Interrupting rating of breakers coordinated with available fault current
Circuit directories required at each panel

Test standards

UL 67: panelboards
NFPA 70 (NEC): panelboards, working space, and branch-circuit protection

Components

Enclosure and trim: steel box with door and dead-front
Bus and neutral bar: copper or aluminum
Breakers: branch and feeder breakers, AFCI and GFCI types
Grounding bar and surge protection

Detailing

Provide working space in front of panels and dedicated space above
Avoid locating panels in clothes closets, bathrooms, or over stairs
Group panels in electrical closets stacked floor to floor in larger buildings
Allow spare spaces and capacity for future circuits
Coordinate flush panels with wall depth and fire-rated walls

Uses

Specific uses

Branch circuits for lighting, receptacles, and equipment
Tenant and dwelling unit panels
Mechanical equipment power panels
Emergency and standby branch panels

Pros and cons

Pros

Compact and inexpensive distribution
Easy to add circuits in spare spaces
Available with monitoring and smart controls

Cons

Limited capacity per panel
Working space and access needed in finished spaces
Recessed panels conflict with rated and shallow walls

Manufacturing and cost

Construction

Factory-assembled interiors and tubs; box roughed in during framing, interior and trim installed after wiring

Main manufacturers and suppliers

Trade associations: NFPA and NECA.

Sources

GlobalSpec: UL 67 panelboards, https://www.globalspec.com/industrial-directory/ul_67_panelboards
Washington University: 09 panelboards design standard, https://facilities.med.wustl.edu/app/uploads/2019/10/09_Panelboards.pdf
Newfoundland and Labrador: Division 26 master specification index (26 24 16 panelboards), https://www.gov.nl.ca/ti/works/masterspec/div26
EC&M: NEC requirements for working clearances, https://www.ecmweb.com/national-electrical-code/code-basics/article/21259374/nec-requirements-for-working-clearances
Wikimedia Commons: EEUU(GE)BreakerpanelInnards.jpg, by unknown author (Public domain), https://commons.wikimedia.org/wiki/File:EEUU(GE)BreakerpanelInnards.jpg