Five years ago, EV charging was a line item developers added for marketing. Today it is a code requirement in a growing list of jurisdictions, a tenant expectation in commercial buildings, and — from the electrical engineer's chair — one of the largest new loads a building design has absorbed in decades.
This guide covers what EV charging actually adds to a building's electrical load, why naive addition breaks the design, how load management changes the answer, and what a proper EV charging electrical design must include.
Charger Types and What They Draw
EV charging hardware falls into three practical tiers:
- Level 1 / domestic socket charging — roughly 1.4–2.3 kW from an ordinary outlet. Slow, and rarely part of a building design beyond residential garages.
- Level 2 / AC wallbox charging — the workhorse for buildings: about 7.4 kW single-phase (32 A at 230 V), 11 kW three-phase (16 A), or 22 kW three-phase (32 A).
- DC fast charging — 50 kW and up, with highway units now reaching 150–350 kW. These are substation-scale loads and belong in a dedicated design exercise.
The arithmetic turns alarming quickly. Ten 22 kW wallboxes is 220 kW of connected load — comparable to several floors of offices — added to a car park that previously drew little more than lighting and ventilation.
Connectors and Regional Standards
The connector landscape is settling but still regional: Type 2 dominates AC charging across Europe, the Gulf and most IEC markets, with CCS2 as its DC counterpart, while North America is converging on the NACS connector alongside legacy CCS1. For a building design the practical implication is simple — specify the socket standard of the market, prefer socketed (cable-free) AC units in shared car parks for durability, and check that any DC hardware matches the fleet it is meant to serve before the civil works fix its position.
Why You Don't Just Add It Up
If every charger were assumed to run at full power simultaneously, most existing buildings could not host more than a handful, and new designs would carry absurdly oversized transformers. The saving grace is the same principle that governs every load schedule: diversity. Cars arrive at different times, most sessions taper off well before the car leaves, and a vehicle parked for nine hours does not need nine hours at 22 kW.
How much diversity to claim is a design decision that depends on the use case. A workplace car park where cars sit all day justifies aggressive diversification; a retail site with 45-minute dwell times does not. Codes and utilities increasingly publish their own assumptions, and where an active load management system is installed, many allow the managed maximum — not the connected total — to be used in the demand calculation.
Active Load Management
An automatic load management system (ALMS) measures the building's spare capacity in real time and shares it dynamically across the chargers — slowing or pausing sessions as building demand peaks, accelerating them overnight. The practical effect is dramatic: a feeder sized for four unmanaged chargers can often serve ten or more managed ones, with barely perceptible impact on drivers. For retrofit projects on buildings with no spare transformer capacity, load management is usually the difference between feasible and impossible.
EV charging is sized on managed demand, not connected load. The load management strategy is an electrical design decision — made before panels and transformers are sized — not an accessory bolted on after the chargers are bought.
What the Electrical Design Must Cover
A proper EV charging design is a standard piece of electrical engineering with a few sharp edges:
- Demand assessment — the revised building maximum demand with charging included, feeding the transformer and main switchboard check, exactly as in any electrical design
- Dedicated circuits and protection — each charge point on its own circuit with its own overcurrent device, as charger standards and codes require
- Residual current protection — EV circuits need DC-fault-sensitive protection: either a Type B RCD or a Type A device paired with a charger's built-in 6 mA DC detection, per the applicable code
- Cable sizing and voltage drop — car park runs are long and chargers draw continuously at full current for hours, so cables are sized for continuous duty and checked for voltage drop, not just ampacity
- Earthing arrangements — outdoor charging on PME/TN-C-S supplies raises specific earthing requirements that several codes treat explicitly
- Metering and billing provision — tenant charging almost always needs per-point metering, which is far cheaper to design in than to retrofit
A Worked Illustration
Take an office car park whose switchboard has 100 kVA of genuine spare capacity. Unmanaged, that hosts four 22 kW chargers with nothing to spare. With an ALMS capped at the same 100 kVA, the design can install twelve or more charge points sharing that envelope: in the morning plug-in peak each car might see 8 kW instead of 22 kW, and by mid-morning — as early sessions taper — the system redistributes the headroom automatically. Every car parked for the working day still leaves full. The infrastructure cost per usable charge point drops to a fraction, which is why the demand assessment and the management strategy must be designed together.
Metering, Billing and Communications
Chargers in shared buildings are rarely free to use, so the design must decide early how energy is measured and recovered: MID/revenue-grade metering per point, integration with the landlord's tenant billing, or a networked charging platform. Most commercial chargers now speak OCPP — the open protocol that lets hardware from different vendors run under one back office and one load management scheme. Specifying OCPP compliance, and the LAN or SIM connectivity behind it, keeps the owner free to change operators later; omitting it quietly hands the site to a single vendor. These are electrical design decisions in the practical sense: they determine the small-power, containment and network provisions on the drawings.
Future-Proofing: The Cheapest Decision on the Project
Charging demand only moves one way, and the gap between "EV-ready" and "EV-capable" is mostly civil work. Containment routes, spare conduits, panel space, a transformer margin and room layout that accepts a second feeder cost very little at construction and a fortune afterwards. Many codes now mandate a percentage of EV-ready bays in new developments precisely because retrofitting trenches through a finished car park is the most expensive way to lay a cable ever devised.
A sensible new-build brief: install chargers for today's demand, containment for five years' demand, and capacity provision for the car park going fully electric. The incremental design cost is small; the option value is enormous.
Conclusion
EV charging is no longer an accessory load — in many buildings it is becoming the largest single addition to the demand schedule. Designed naively, it breaks transformers and budgets; designed properly, with realistic diversity, active load management and future-proofed infrastructure, it fits into buildings that were never planned for it. The engineering is well within standard electrical design practice — it just has to be done deliberately, and early.