Power distribution design

Power distribution design decides how electricity gets from the utility connection to every panel in the building: what voltage it travels at, where it is transformed, how it is protected and how much room is left for the future. We design distribution for new buildings, additions and major renovations, and redesign it where an existing system has run out of capacity or reliability.

Most of the cost, reliability and safety of a building's electrical system is set by the distribution layout. A well-arranged system puts transformers close to the loads they serve, keeps feeders short, isolates faults to the smallest possible area and leaves space in the switchboard for loads nobody has thought of yet. A poorly arranged one tends to show up years later as full panels, long outages for simple repairs and expensive workarounds.

What we design and build

• Service entrance equipment, main switchboards and switchgear, coordinated with the utility.
• Distribution voltage choices, such as 347/600 V for larger buildings and 120/208 V for smaller ones.
• Transformer sizing and placement, including step-down transformers serving floors or tenant areas.
• Distribution panels, panelboards and motor control centres, with spare capacity and spare space.
• Feeder sizing, routing and voltage drop checks.
• Metering arrangements for tenants, sub-metering and energy monitoring.
• Connections for emergency and standby power, and isolation for maintenance.
• Grounding, bonding and surge protection at the service and major equipment.

How the system is arranged

In a typical Canadian commercial building, power arrives from the utility at medium voltage and is stepped down by a utility transformer to 347/600 V. The main switchboard divides it into feeders. Large motors and 347 V lighting run directly at that voltage, while dry-type transformers in electrical rooms step it down again to 120/208 V for receptacles, computers and small equipment.

Larger or more critical facilities add redundancy: two utility feeds, a double-ended switchboard with a tie breaker, or a separate emergency distribution system fed through transfer switches. The right arrangement depends on how much an outage costs you and how often equipment will need to be shut down for maintenance.

How it works

1. Brief. We start by asking why: new building, added load, poor reliability, a change of use or a utility requirement. We gather the expected loads, critical equipment and growth plans.
2. Existing conditions. In existing buildings we survey the switchboard, transformers and panels, read nameplates and compare the single-line diagram and schedules with what is installed. Twelve months of utility demand data shows how the building actually behaves.
3. Concept. We propose a distribution arrangement, voltages and equipment locations, and coordinate with the utility on the service connection. This is where you choose how much redundancy and spare capacity to pay for.
4. Detailed design. We size feeders and transformers, check voltage drop and available fault current, and produce the single-line diagram, panel schedules, layouts and specifications. Drawings for permit are sealed by a licensed professional engineer where required.
5. Construction and close-out. Installation is done by licensed electrical contractors under permit. We review shop drawings, visit site, review the installed work and update drawings to show what was built.

What to have ready

• Existing single-line diagrams, panel schedules and electrical room drawings, even if they are out of date.
• Twelve months of utility bills or interval data showing peak demand.
• A list of planned equipment and tenants, and any loads that must stay on during an outage.
• Records of past outages, nuisance trips or overheating problems.
• Previous studies: short-circuit, coordination, arc flash or thermography reports.
• Who needs to be told about shutdowns, and the windows when they can happen.

What you get

A single-line diagram showing every major piece of distribution equipment, its rating and how it is fed. Panel and equipment schedules with spare capacity identified. Layouts of electrical rooms with working clearances shown. Specifications for switchgear, transformers and panels. The load calculation and voltage drop checks behind the design, and, where the project calls for them, short-circuit and coordination studies.

The drawings are written to stay useful after construction. Facility staff, future designers and the contractor who comes in at 2 a.m. to restore power all work from the same single-line diagram, so it needs to be accurate and readable.

A typical case

An office building from the 1980s has a 120/208 V service, panels that are full on every floor, and tenants asking for more power. Adding capacity at 120/208 V would mean very large feeders. A study of the options might show that converting the main distribution to 347/600 V, with a step-down transformer and new panelboards on each floor, gives more capacity for less copper and leaves room for EV chargers in the parkade. The work is phased floor by floor with short planned shutdowns, and the single-line diagram is updated at each phase so the building is never running on drawings that do not match.

Who it's for

• Developers and owners planning new buildings or additions.
• Facility managers whose panels are full or whose service is near its limit.
• Industrial and institutional sites where outages are costly.
• Property managers converting buildings to new uses or splitting them for multiple tenants.

To learn more, read how power gets from the street to the outlet, single-line diagrams explained, transformers in commercial buildings and 120/208 V vs 347/600 V systems.

Common questions