EV load management

EV load management controls how much power each charger draws so that many chargers can share a limited amount of electrical capacity. Instead of sizing the service for every charger running flat out at once, the system shares the available power among the vehicles that are actually charging, and holds the total within a set limit. For most multi-unit residential and workplace projects, it is the difference between adding chargers to the existing service and paying for an upgrade.

Why it works

Vehicles rarely all need full power at the same time. Some arrive with nearly full batteries, some leave early, and most are parked far longer than it takes to charge. If a parkade has many Level 2 spaces, sharing a fraction of their combined rating across them still gives most drivers the range they need overnight or over a workday. Load management makes that sharing automatic and safe.

The Canadian Electrical Code recognizes this. It allows the load of EV charging equipment that is controlled by an electric vehicle energy management system (EVEMS) to be calculated on the basis of the limit the system enforces, rather than the full rating of every charger, subject to the code's conditions. Check the edition adopted in your province and confirm the approach with the inspection authority early in the design.

The main approaches

Circuit sharing

Two or more chargers share one circuit. The chargers communicate, or a switching device alternates between them, so the circuit is never overloaded. It is simple and cheap, and it suits small numbers of chargers where drivers do not all need to charge at the same time.

Static group limit

A group of chargers is fed from a panel with a fixed total limit. The charging network or the chargers themselves divide that limit among the vehicles connected. The limit is set low enough that, added to the building's maximum load, the service is never overloaded. It is predictable, but it does not use spare capacity when the building's other loads are low.

Dynamic load management

The system measures the load on the service or feeder in real time, typically with current sensors, and gives the chargers whatever capacity is left after the building's other loads, up to a set ceiling. At night, when the building's load is low, the chargers get more. On a cold morning when heating peaks, they get less. This uses the existing service most fully, but it relies on the measurement, the communication and the control system working correctly.

Comparing approaches

What drivers experience

Load management changes the charging rate, not whether charging happens. When few vehicles are plugged in, each gets close to full power. When many are connected, each gets less. Most systems let the operator set priorities, such as a minimum rate for every vehicle, or more power to vehicles that have been connected the shortest time. For overnight residential charging, most drivers never notice. For workplaces with short stays or fleets with tight schedules, the settings need more thought.

What to check before relying on it

• The system and chargers are certified, and the EVEMS meets the code conditions for reducing the calculated load
• The limit is based on a proper load calculation of the building's other loads, including the winter peak
• The system fails safe: if communication or a sensor is lost, chargers drop to a safe low rate or stop, rather than running at full power
• Current sensors are installed at the right point and measure all phases
• Settings are documented, protected from casual changes and kept with the electrical records
• There is a plan for adding chargers later, and for what happens when the group reaches its practical limit
• Someone is responsible for monitoring the system and responding to faults

How a managed charging project is designed

1. Establish the capacity. Measure or calculate the building's existing peak, across all seasons, and work out what is genuinely available for charging.
2. Understand the drivers. How many vehicles, how long they park, and how far they typically drive. This sets the minimum energy each vehicle needs per session.
3. Choose the approach. Circuit sharing, a static limit or dynamic management, based on the capacity available and the number of chargers planned.
4. Design the distribution. Panels, feeders and circuits sized for the managed load, with room for future chargers. Drawings for permit are sealed by a licensed professional engineer where required.
5. Install and commission. A licensed electrical contractor installs the work under permit. Commissioning tests the limit, the failure behaviour and the priority settings with vehicles connected.
6. Review after occupancy. Check charging logs after a few months and adjust settings if drivers are not getting the energy they need.

A typical case

A condominium building with an older service wants to give every owner the option of a charger in their stall. A load calculation shows enough spare capacity for only a handful of chargers at full output, and a service upgrade would be expensive and slow. The design that results feeds a new EV panel from the existing service, with a dynamic EVEMS that measures the building's total load. Overnight, when the building's load is low, connected vehicles share a generous amount of power. On the coldest evenings, when the electric heating in common areas peaks, the system automatically reduces charging. Every owner who wants a charger can have one, and the board can decide later whether demand justifies a service upgrade. For the governance side of projects like this, see EV charging in condos and multi-unit buildings.

How ehZee can help

Our EV charging design service checks your building's capacity, recommends the load management approach that fits, and designs the panels, circuits and controls. We look at how drivers will use the chargers so the settings work in practice.

Common questions