Designing an Electrical Room — More Than Just Empty Space
There is a unique kind of silence inside an electrical room.
No audience. No decoration. Just concrete walls, humming equipment, heat, controlled airflow, and invisible power waiting behind steel doors.
Yet some of the most critical engineering decisions in any building happen here.
An electrical room is not simply “a room with panels.” It is a carefully engineered environment where safety, reliability, maintainability, heat dissipation, code compliance, and future expansion all intersect. A well-designed room protects both people and equipment. A poorly designed one can become dangerous long before any electrical failure occurs.
The Purpose of an Electrical Room
An electrical room safely houses power distribution equipment such as:
Switchboards
Panelboards
Motor Control Centers (MCCs)
Transformers
UPS systems
Automatic transfer switches (ATS)
Disconnects
Battery systems
Telecom and low-voltage equipment
The room must support:
Safe operation and maintenance
Proper ventilation and heat rejection
Emergency access and egress
Code-required working clearances
Future modifications and expansion
This is where the National Electrical Code (NEC) becomes essential.
NEC Working Clearance Requirements (Article 110.26)
The foundation of electrical room design is NEC Article 110.26 — Spaces About Electrical Equipment. This applies to equipment operating at 1000V or less.
Minimum Working Clearance Depths (measured from the front of the equipment): Voltage to GroundCondition 1Condition 2Condition 30–150 V3 ft (0.9 m)3 ft (0.9 m)3 ft (0.9 m)151–600 V3 ft (0.9 m)3.5 ft (1.1 m)4 ft (1.2 m)
Condition Definitions:
Condition 1: Exposed live parts on one side only and no live parts or insulated surfaces on the opposite side (e.g., panel facing a concrete wall).
Condition 2: Exposed live parts on one side and grounded parts on the opposite side (e.g., panel facing metal equipment or structural steel).
Condition 3: Exposed live parts on both sides (e.g., two switchboards facing each other). This is the most hazardous arrangement and requires the greatest clearance.
Width Requirements:
Minimum width = width of the equipment or 30 inches (762 mm), whichever is greater.
The working space does not need to be centered but must allow safe access.
Height Requirements:
Minimum 6.5 ft (2.0 m) headroom or the height of the equipment, whichever is greater.
No unrelated equipment (pipes, ducts, lighting fixtures, etc.) may intrude into the working space.
Dedicated Equipment Space — NEC 110.26(E)
Electrical equipment also requires protected vertical dedicated space above it. This space must be:
Equal in width and depth to the equipment footprint.
Extend upward to 6 ft above the equipment or to the structural ceiling (whichever is lower).
Purpose: Prevent water leaks, falling objects, and foreign systems (plumbing, HVAC, etc.) from compromising the equipment. Water above energized gear is one of the most common causes of major electrical failures.
Transformer Room Considerations
Transformers add special challenges:
Heat: Dry-type transformers require excellent ventilation (natural or forced). High ambient temperatures significantly reduce transformer life.
Noise: The characteristic 60 Hz hum can be disruptive. Avoid locating transformer rooms next to offices, classrooms, or conference rooms. Acoustic treatment is often needed.
Vibration and Magnetic Fields: Proper isolation and separation from sensitive equipment is important.
Door and Egress Requirements
Doors are more important than they appear. Per NEC 110.26(C):
Doors must open in the direction of egress.
They must open at least 90 degrees.
For equipment rated 1200 A or more and over 6 ft wide, panic hardware is often required.
In an arc flash event, the last thing anyone needs is a door that is difficult to open.
Arc Flash and Safety Planning
Modern electrical room design must also consider:
Arc flash boundaries and incident energy levels
Proper labeling
PPE storage near the entrance
Safe maintenance access
Minimized crowding
Planning for the Future
One of the most expensive mistakes is designing only for today’s needs. Good electrical rooms anticipate:
Additional panels or switchboard sections
New UPS or battery storage
Solar inverters or EV charging infrastructure
Expanded telecom/low-voltage racks
Spare conduit pathways
Leaving blank wall space and strategic conduit sleeves can save enormous renovation costs later.
Recommended Layout Philosophy
Prioritize clear front working space
Group similar equipment logically
Separate high-heat equipment when practical
Plan ventilation airflow paths carefully
Coordinate conduit and cable tray entries early
Provide adequate (and emergency) lighting
Ensure equipment can actually be delivered, installed, and someday replaced
Common Mistakes to Avoid
Using the room as storage — Violates working space rules and creates serious hazards.
Ignoring heat buildup — Especially with transformers and UPS systems.
Poor multi-trade coordination — Late changes from mechanical, plumbing, or structural teams destroy clearances.
Zero spare capacity — Guarantees expensive future renovations.
Inadequate access paths — Forgetting that large equipment must be removable someday.
Final Thought
Most people never notice a well-designed electrical room. That’s exactly the point.
Behind locked doors and finished walls, these quiet spaces keep hospitals, schools, data centers, factories, and office buildings running safely every single day.
The best electrical rooms are invisible — until something goes wrong. Then everyone remembers why good engineering matters.
1. Main Distribution Panelboards (MDP / SDP)
Purpose: Primary distribution from the switchboard or transformer.
Typical Specs:
480/277V or 208/120V
400A to 1200A (or higher)
Bolt-on or plug-in bus
High AIC rating (65kA–200kA)
Recommendation: Always include at least one main distribution panel per electrical room, with 25–40% spare capacity and space for future sections.
2. Lighting and Appliance Branch-Circuit Panelboards
Most common type in commercial/institutional buildings.
Specs:
208/120V, 3-phase, 4-wire
225A or 400A main
42–84 circuit spaces (42 is standard, but 84 is increasingly common)
Copper bus preferred for reliability
Use for general lighting, receptacles, and small loads.
3. Power Distribution Panelboards (PDP)
For larger loads (HVAC, pumps, motors, elevators, etc.).
Specs:
480/277V or 208/120V
225A–800A
Fewer, higher-amperage circuit breakers (e.g., 100A–400A frames)
Often with surge protection devices (SPDs)
4. Emergency / Legally Required Standby Panelboards
Fed from automatic transfer switch (ATS).
Color coding recommended (red for emergency).
Separate from normal power panels.
Must comply with NEC Article 700 / 701.
5. Optional / Future Panels to Plan For
Panel TypeVoltageTypical UseSpare RecommendationUPS / Critical Load Panel208/120VServers, medical equipment, PoE30–50% spareEV Charging Panel208/120V or 480VElectric vehicle chargersGrowing demand — plan aheadRenewable / Solar Inverter Panel480V or 208VPV system tie-in20–30% spareHVAC / Mechanical Panel480VChillers, AHUs, pumpsHigh priorityFire Alarm / Life Safety Panel120VDedicated fire alarm powerCode requiredTelecom / Low Voltage Panel208/120VNetwork racks, DAS, securityOften integratedBattery Storage / BESS Panel480VEnergy storage systemsFuture-proofing
Design Best Practices for Adding Panelboards
Spare Capacity:
Minimum 25–35% spare breakers/spaces in new panels.
Minimum 20–30% spare physical wall space in the electrical room for future panels.
Bus Material: Copper bus is strongly preferred over aluminum for long-term reliability (especially in humid or coastal areas like Hawaii).
AIC Rating: Match or exceed the available fault current at the location (calculate during design).
Mounting:
Wall-mounted for smaller panels (<400A)
Floor-mounted (free-standing) for larger distribution panels
Location Strategy:
Group normal power panels on one wall.
Separate emergency/UPS panels on another wall.
Maintain full NEC 110.26 working clearances in front and a dedicated space above.
Future-Proofing:
Install extra 4-inch conduit sleeves from the electrical room to the main switchboard or roof.
Leave blank sections in switchboards for future panel feeders.
