EV Charging Without a Service Upgrade: How EVEMS Changes the Game

A building owner wants 50 EV chargers. The utility quotes a costly service upgrade. Here's how EVEMS technology lets you install those chargers on your existing electrical service - legally and safely.

The Problem: EV Load vs. Existing Capacity

The transition to electric mobility has placed unprecedented strain on existing building electrical systems. A standard Level 2 EV charger typically draws up to 40A on a dedicated circuit at 208V/240V. EV chargers are treated as continuous loads (Section 86), and under standard CEC load calculation rules (Section 8) without an energy management system the full EVSE rating must be added to the service calculation at 100%.

The math is brutal. If a condo board wants to install 20 Level 2 chargers at 40A each:

20 chargers × 40A × 208V = 166 kVA of additional demand
That's roughly equivalent to adding an entire second building to your electrical service.

For existing buildings, upgrading a main service from 600A to 1200A - or upgrading the utility transformer - can be a major capital cost and can take several months of utility lead time. This is the wall that kills most retrofit EV projects before they start.

For a single house, the panel upgrade guide works through whether your house needs 200 A for a charger, with and without an energy management system.

The Solution: CEC Section 86 & EVEMS

The Canadian Electrical Code (CEC), adopted in Ontario as the OESC, explicitly recognizes a smarter approach: the Energy Management System (EMS, Rule 8-500; called EVEMS before the 2024 edition). An EMS is a control system (monitors, controllers, timers or communications equipment) that monitors building or circuit load in real-time and dynamically throttles EV charger output to keep the total demand within the existing service capacity.

OESC Rules 8-106 10) and 11), 8-500 & 86-300 2): When an EMS guarantees that total EV load will never exceed a defined setpoint, the engineer can use the EMS-managed load - not the raw charger nameplate - in the service calculation.

How Power Sharing Works

Instead of providing 40A continuously to 20 cars (800A total), an EVEMS might be fed from a single 200A panel rated for 100% continuous load (with standard 80%-rated equipment the EMS limit is 160A, Rule 8-104). The system dynamically distributes available capacity:

Overnight - when most charging happens - cars finish sequentially. As each vehicle reaches 100%, the system redistributes its share to the remaining vehicles. By morning, each car has typically received a useful top-up, though not necessarily a full charge.

Sharing an existing service among many chargers

A typical parking level, not a design. Power-sharing values from the article’s example.

Electrical points

1. 1

   Existing service: without an EMS the full EVSE rating is added at 100 % (continuous loads, Section 86): 20 chargers × 40 A × 208 V = 166 kVA of new demand.

2. 2

   200 A EV panel: rated for 100 % continuous load; with standard 80 %-rated equipment the EMS limit is 160 A. Rule 8-104

3. 3

   Energy management system: monitors load and throttles the chargers so the total never exceeds the setpoint; the EMS-managed load is used in the calculation. Rules 8-106 10), 11), 8-500, 86-300 2)

4. 4

   Level 2 chargers: 40 A at 208/240 V, 7.7–9.6 kW; networked so the EMS can manage them (non-networked chargers can only be switched on or off).

5. 5

   DC fast charger: 480 V, 100–400 A circuits, 50–350 kW; requires integration with the load management.

6. 6

   EV-ready conduit: empty conduits to the stalls placed during construction cost far less than retrofits.

7. 7

   Voltage drop: long runs to parking stalls must stay within 3 % for the branch circuit and 5 % overall. Rule 8-102

• Circuits in conduit
• Load-management network
• EMSEnergy management system

Figure 1. Sharing an existing service among many chargers

Charger Types: Level 1, Level 2, and DCFC

Design Considerations for New Builds

Even when chargers aren't installed on day one, smart engineering during construction saves enormous costs later:

• "EV Ready" conduit: Run empty conduits from the electrical room to parking stalls during the concrete pour - retrofitting conduit later costs significantly more
• Panel capacity: Allocate physical breaker space and spare distribution capacity for future EVEMS panels
• Network infrastructure: Networked EVEMS and billing platforms need reliable Wi-Fi, cellular or wired connectivity in the parking garage for remote load management and billing
• Metering strategy: Decide early whether chargers will be individually metered (tenant billing) or bulk-metered (common area cost)

Cost Comparison: Service Upgrade vs. EVEMS

Common Engineering Mistakes

• Treating each charger as a dedicated 40A load - an EMS removes this requirement under OESC Rules 8-106 10) and 8-500
• Ignoring conductor voltage drop - long runs to underground parking often exceed the Rule 8-102 limits (3% for the branch circuit, 5% overall)
• Not future-proofing conduit - the cost of adding conduit after the slab is poured is astronomical
• Specifying non-networked chargers - dumb chargers can only be managed by switching their supply on or off

Frequently Asked Questions