This guide covers the code requirements every panel must meet, general placement principles, main and subpanel locations for residential, commercial, office and school buildings, and a guide to sizing electrical rooms.
Note: This overview is based on US practice —code references follow the model 2023 NEC (Articles 110, 230 and 240). Utility rules often govern the meter and service location and should be checked early in design.
1. Code requirements for every panel
Wherever a panel goes, it needs a clear box of working space in front, dedicated space above, easy access and a location free of the hazards the NEC lists.
Working and dedicated space (NEC 110.26)
Requirement | Rule |
Working space depth | 3 ft for systems up to 150 V to ground; 3, 3½ or 4 ft for 151–600 V depending on what faces the panel (insulated, grounded such as concrete or masonry, or exposed live parts) |
Working space width | 30 in or the equipment width, whichever is greater; doors must open at least 90° |
Working space height | 6½ ft or the equipment height, whichever is greater |
Dedicated space | Footprint of the equipment, from the floor to 6 ft above it or the structural ceiling; no piping, ducts or other foreign systems |
Storage | Working space may not be used for storage |
Illumination | Lighting in the working space, not controlled by automatic means only |
Entrances | Equipment 1,200 A or more and over 6 ft wide needs an exit at each end of the working space (24 in wide, 6½ ft high), with exceptions |
Doors | Equipment 800 A or more: personnel doors within 25 ft of the working space swing outward with listed panic hardware |
Location rules for panels and breakers (NEC 240.24, 230.70)
- Readily accessible; the top breaker handle no more than 6 ft 7 in above the floor.
- Not in clothes closets or near easily ignitible material.
- Not in bathrooms of dwellings, dormitories or hotel rooms; service disconnects not in any bathroom.
- Not over the steps of a stairway.
- Protected from physical damage and suited to the environment (wet, corrosive, hot).
- Occupants of each dwelling unit, and of each guest room with permanent provisions for cooking, must have access to their own overcurrent devices.
- The service disconnect is readily accessible, outside or inside at the nearest point where service conductors enter; up to six disconnects per service in separate enclosures or compartments.
- One- and two-family dwellings need an outdoor emergency disconnect (NEC 230.85).
Working space: Open Exam Prep. Overcurrent device locations: EC&M. Service disconnects: Open Exam Prep.
2. Placement principles
The main panel goes where the utility service enters; subpanels go near the loads they serve. Everything else follows from keeping circuits short and equipment reachable.
Principle | What it means | Typical target |
Main panel at the service entrance | The service disconnect must be at the nearest point where service conductors enter the building | Utility-approved meter location; exterior wall near the transformer |
Subpanels at the load center | Place each subpanel near the middle of the area it serves | Branch circuits mostly under 75–100 ft at 120 V and 150–200 ft at 277 V |
Separate buildings get their own panel | Each detached structure with power has a disconnect where the feeder enters | Garage, ADU, portable classroom, site lighting enclosure |
Stack vertically | Electrical rooms on each floor aligned over each other | Short, straight risers in multistory buildings |
Cluster by voltage | 480Y/277 V lighting and mechanical panels near 208Y/120 V receptacle panels and their transformer | One electrical room per floor or wing |
Near large loads | Dedicated panels or MCCs beside mechanical rooms, kitchens and data rooms | Short feeders to chillers, kitchen equipment, IT racks |
Secure from the public | Panels in locked rooms or staff areas in commercial buildings | Corridors and public spaces only with locking covers |
Room for growth | 20–25% spare capacity and spaces; spare conduits or sleeves to upper floors | Plan wall space for a future panel in each electrical room |
Separate emergency equipment | Emergency panels, transfer switches and inverters apart from normal equipment where required | Separate room or protected area in larger buildings |
Avoid hazards | Away from water piping, below-grade flood zones, high heat and corrosive areas | Not under plumbing; above the design flood elevation |
3. Residential
3.1 Single-family homes
The meter and main disconnect go on an exterior wall where the utility can reach them; the load center goes inside on the other side of that wall or close to it.
Panel | Typical location | Rules and practice |
Meter and outdoor emergency disconnect | Exterior wall, usually on the side facing the utility line or transformer | Utility-approved location; outdoor emergency disconnect required for one- and two-family dwellings, marked "EMERGENCY DISCONNECT" (NEC 230.85) |
Main load center | Garage wall, basement, utility or laundry room, back-to-back with the meter | Readily accessible; 30 in wide by 3 ft deep working space; not in clothes closets, bathrooms or over stairs |
Combination meter-main outdoors | Exterior wall, with the branch panel inside | Common in warm climates; serves as the main and emergency disconnect |
Subpanel for an addition or second floor | Central hallway, laundry room or garage near the new loads | Fed from the main; reduces long runs to remote rooms |
Garage or workshop subpanel | Inside the garage near the door | Common for EV chargers, shop tools |
Detached garage or ADU panel | Inside the building, near where the feeder enters | Disconnect, grounding electrode and isolated neutral required |
Solar, battery and generator equipment | Next to the main panel or meter | Transfer switch or interconnection equipment beside the main |
Places to avoid: clothes closets, bathrooms, over stairs, behind cabinets or appliances, under sinks or plumbing, crawl spaces and attics (hard to reach), and below-grade areas prone to flooding.
3.2 Multifamily buildings
Panel | Typical location | Rules and practice |
Main switchboard and meter stacks | Ground-floor or basement electrical room near the utility transformer; meter banks on each floor or every few floors in high-rises | Locked room accessible to building staff and the utility |
House panel | Main electrical room | Common-area lighting, laundry, elevators, site lighting |
Unit load center | Inside each unit: hallway, laundry closet (not a clothes closet), kitchen or entry wall | Must be accessible to the occupant; not in bathrooms or clothes closets (NEC 240.24) |
Fire pump and emergency equipment | Separate rated room where required | Fire pump tapped ahead of the main disconnect |
EV charging panels | Parking garage, near the charging stalls | Load-managed systems reduce feeder size |
Each dwelling unit's occupant must have ready access to the overcurrent devices serving that unit (NEC 240.24(B)).
4. Commercial and retail
The main switchboard sits in a ground-floor electrical room on an exterior wall near the utility transformer. Each tenant then gets its own panels inside the tenant space, usually in a back-of-house room.
Panel | Typical location | Rules and practice |
Utility transformer | Pad outside, near the electrical room, with clearances set by the utility | Keep feeders to the switchboard short |
Main switchboard and tenant meters | Ground-floor electrical room on an exterior wall, often with an exterior door | Service disconnect at the nearest point of entrance; two exits for large equipment (Section 1) |
House panel | Main electrical room | Site and parking lighting, common areas, signage |
Tenant panels | Back-of-house electrical closet or stockroom wall in each tenant space | Locked or staff-only; working space kept clear of stock |
Restaurant kitchen panel | Kitchen or adjacent electrical room, away from cooking lines and wash-down areas | Near the equipment it serves; shunt-trip controls for hoods |
Refrigeration panel (grocery) | Mechanical or compressor room | Beside refrigeration racks |
Rooftop equipment | Disconnects at each unit on the roof | Panels themselves stay indoors where possible |
Exterior lighting contactor | Main electrical room or tenant panel location | With the time clock and photocell controls |
Common problem: stock and fixtures piled in front of tenant panels. Mark the required working space on the floor and keep panels out of sales areas.
5. Offices
Offices put the main switchboard in a ground-floor or basement room near the utility transformer, then stack an electrical room on every floor in the building core directly above it, so a single straight riser feeds each floor.
Panel | Typical location | Rules and practice |
Main switchboard or switchgear | Ground-floor or basement main electrical room on an exterior wall near the transformer; above flood level | Exterior door for equipment replacement; two exits for large equipment |
Riser (busway or feeders) | Vertical shaft through the stacked electrical rooms | Fire-rated shaft or sleeves sealed at each floor |
Floor lighting and receptacle panels | Electrical room in the core on each floor, beside the stair, elevator or restrooms | Center of the floor plate so branch circuits stay short; 1–2 rooms per floor depending on size |
Step-down transformer | In each floor electrical room, beside the receptacle panels | Ventilation and clearance to combustibles |
Tenant panels | Floor electrical room, or a tenant electrical closet for large tenants | Tenants may need their own meter and room for added panels |
Mechanical panels and MCCs | Mechanical room or penthouse beside chillers, air handlers and pumps | Rooftop units get disconnects at the equipment |
Emergency and standby panels | Separate room or rated area beside the transfer switches; generator outdoors or in a rated room | Separation rules for life-safety equipment |
IT and data room panels | Inside or beside the data room | UPS and dedicated cooling nearby |
Floor-plate rule of thumb. One floor electrical room typically serves 10,000–25,000 sq ft; larger floors add a second stacked room at the opposite end of the core so circuits stay within about 100 ft at 120 V.
6. Schools
Schools put the main switchgear in a secure ground-floor room near the service entrance, then place an electrical room in each wing so classroom circuits stay short. Every panel is kept out of student reach.
Panel | Typical location | Rules and practice |
Main switchgear | Ground-floor main electrical room on an exterior wall near the utility transformer or campus substation | Locked; exterior access door for utility and fire department where possible |
Wing lighting and receptacle panels | Electrical room or closet in each wing or floor, near the center of the classrooms it serves | Locked rooms off corridors, not inside classrooms |
Kitchen panel | In or beside the kitchen, away from wash-down areas | Shunt-trip under hoods |
Lab and shop panels | Adjacent prep room or staff area | Emergency-off controls in the classroom; panel itself out of student reach |
Gym and auditorium panels | Equipment room or stage-side room | Stage dimming racks near the stage |
Mechanical panels and MCCs | Mechanical room or central plant | Beside chillers, boilers and air handlers |
Emergency and standby panels | Separate room or protected area with transfer switches | Generator outdoors or in a rated room |
Portable classroom panels | Inside each portable, fed from a nearby panel or site distribution | Separate-building disconnect and grounding rules |
Campus unit substations | Outdoor pad or ground-floor room at each building on a campus loop | Medium-voltage clearances and utility or campus standards |
Security. In schools, panels in corridors or classrooms invite tampering. Put them in locked electrical rooms or behind locking covers, and feed each wing on its own feeder so maintenance or a fault in one wing does not shut down the others.
7. Electrical room sizing guide
Room size is set by the equipment's footprint plus its working space; these are early planning allowances to reserve space before the engineer lays out the equipment.
Room | Typical contents | Typical planning size |
Residential panel location | Load center | Wall space 30 in wide, 3 ft clear in front, floor to 6.5 ft |
Apartment building main electrical room | Switchboard, meter stacks, house panel | 150–400 sq ft depending on unit count |
Retail tenant electrical closet | One or two panels, transformer for small tenants | 30–80 sq ft |
Office floor electrical room | 480Y/277 V lighting panel, 1–2 receptacle panels, dry-type transformer, riser or busway | 80–150 sq ft per floor (for floors up to about 25,000 sq ft) |
Office or school main electrical room | Main switchboard, distribution panels, transformers | About 1–2% of building floor area for small to mid-size buildings; often 400–1,500 sq ft |
School wing electrical room | Lighting and receptacle panels, transformer | 60–120 sq ft per wing |
Emergency electrical room | Transfer switches, emergency panels, inverter | 100–300 sq ft |
Planning checklist
- Reserve wall space for 20–25% more panels than the initial design.
- Provide two exits where large equipment (1,200 A or more, over 6 ft wide) requires them; doors near 800 A equipment swing out with panic hardware.
- Keep piping, ducts and roof drains out of the dedicated space above equipment.
- Provide ventilation for transformers and lighting with a manual switch.
- Leave a clear path for replacing the largest piece of equipment.
These sizes are rules of thumb from general design practice, not code values; final sizes come from the equipment layout and NEC 110.26 clearances.
Sources
- Working space, access, egress and illumination, NEC 110.26, Open Exam Prep
- Code Q&A: acceptable locations for overcurrent devices, EC&M (NEC 240.24)
- Service disconnecting means and equipment, Open Exam Prep (NEC 230.70, 230.71, 230.85)
- Feeders and outside branch circuits, Articles 215 and 225, Open Exam Prep
Panel locations by building type, circuit-length targets and room sizes are from general design practice, not these sources; confirm with the adopted code, the utility's service requirements and the project engineer.