🔋 Multifamily and EV Charging Load Calculation Example

Why Multifamily and EV Load Calculations Are More Complex

A multifamily building's load calculation has to account for both individual dwelling unit loads (calculated similarly to a single-family home, per unit) and house loads (common-area lighting, elevators, shared laundry, common HVAC) that serve the whole building rather than any one unit — with Article 220 providing specific demand factor structures for multiple dwelling units that reflect the diversity of many units not all peaking simultaneously. Adding EV charging infrastructure introduces a further layer: EV load is one of the fastest-growing and most actively revised areas of the code (see this site's NEC 2026 update summary), and how it's calculated depends heavily on whether the project uses a fixed per-space load assumption or an EV energy management system (EVEMS) that actively limits aggregate demand.

The Scenario

A representative example: a 24-unit multifamily building, each unit similar to the residential example (roughly 32,000 VA calculated demand load per unit before multi-unit demand factoring), common-area house loads of 25,000 VA connected, and a shared parking garage with 24 Level 2 EV charging spaces (each nominally 7.2 kW / 30A).

Step 1 — Dwelling Unit Loads with Multi-Unit Demand Factor

Article 220 provides a demand factor table specifically for multiple dwelling units on a single service or feeder, reflecting that 24 units' individual peak loads don't all occur simultaneously — the applicable demand factor decreases as the number of units increases. Using an illustrative structure: 24 units × 32,000 VA = 768,000 VA connected before demand factoring; applying a multi-unit demand factor appropriate for this unit count (commonly in a range that could reduce this to somewhere around 45-55% of the connected total for a building this size, though the exact percentage depends on the specific unit count and code edition) — illustratively, 768,000 × 0.50 ≈ 384,000 VA.

Step 2 — House Loads

Common-area loads (lobby/corridor lighting, elevators, shared laundry, common-area HVAC) are calculated separately and are not subject to the dwelling-unit demand factor, since they serve the whole building rather than individual units: 25,000 VA connected, with any applicable continuous-load or specific-equipment demand considerations applied per their own code provisions — using this value directly for this illustrative example: 25,000 VA.

Step 3 — EV Charging Load, No Load Management

Without an EV energy management system, each charging space's load is typically counted at or near its full continuous rating (with the 125% continuous-load factor applied, since EV charging commonly runs 3+ hours): 24 spaces × 7,200 W × 1.25 = 216,000 VA. This is a very large addition relative to the building's other loads — a common reason EV retrofit projects in existing multifamily buildings run into service capacity constraints without load management.

Step 3 (Alternative) — EV Charging Load With Load Management

An EV energy management system actively limits the aggregate demand of the charging spaces to a set maximum, rather than assuming every space charges simultaneously at full rate — the NEC's more recent EV charging provisions specifically recognize EVEMS as a way to calculate load based on the system's configured maximum aggregate demand rather than the sum of every individual charger's nameplate rating. If this building's EVEMS is configured to cap aggregate EV demand at, say, 100,000 VA regardless of how many vehicles are actively charging: the calculated EV load becomes 100,000 VA — a substantial reduction from the no-management scenario, and often the deciding factor in whether a multifamily EV retrofit requires a service upgrade at all.

Step 4 — Total and Comparison

Without load management: 384,000 + 25,000 + 216,000 = 625,000 VA total. With load management: 384,000 + 25,000 + 100,000 = 509,000 VA total. At 480Y/277V three-phase, this difference (roughly 116,000 VA) can be the difference between requiring a substantial electrical service upgrade and being able to add EV charging within existing service capacity — illustrating why EVEMS-based load calculation has become one of the more consequential recent additions to how EV charging is treated under Article 625's interaction with Article 220.

What This Means for Multifamily EV Retrofit Projects

For existing multifamily buildings adding EV charging where a service upgrade would be expensive or disruptive, evaluating whether an EVEMS-based calculation brings the project within existing service capacity is often the single highest-leverage design decision — worth exploring before assuming a service upgrade is required based on a no-load-management worst-case calculation.