Do You Have Capacity for EV Chargers? Probably Not Without a Demand Study.

Nameplate vs measured capacity

Every EV charger conversation starts with the same question: 'how much capacity do we have spare?' The instinct is to add up nameplate ratings on the panel schedule and call that the answer. It's almost always wrong. NEC Article 220 demand factors (which the building was sized to) assume diversified load — but actual measured load in commercial buildings runs 35–60% of nameplate during peak. So the real spare capacity is usually 40–65% more than the panel schedule suggests. The catch: NEC 705 (and 750 for EV specifically) requires you to add the new EVSE load to the *calculated* load, not the *measured* one. So even if you have headroom, you might not have it on paper.

What a demand study actually does

A 14-day demand study clamps a meter on the main service and logs every 15-minute interval. At the end, you have a defensible measured peak — the highest 15-minute average over the two weeks — and a load profile showing when the building actually draws power. With that data, NEC 220.87 lets you use the *measured* peak (with a 1.25× safety factor) for sizing new loads instead of the conservative calculated value. For most commercial buildings, that swing is the difference between adding 12 Level 2 chargers without an upgrade vs. needing a new service entrance.

What the study usually reveals

Three typical outcomes from a two-week demand study on a mid-sized commercial building: (1) a service whose calculated load looks tight but whose measured peak is far below — meaning you can add a meaningful number of Level 2 chargers without touching the service entrance; (2) a service that already has limited headroom and supports a few chargers via a managed-charging subpanel; (3) a service that's running closer to its calculated limit than expected, which makes EV install contingent on a service upgrade. Knowing which of the three you are before the bid changes everything about how the project is scoped — and avoids the worst outcome, which is an unbudgeted upgrade discovered mid-install.

When you can skip the study

If you're adding fewer than three Level 2 chargers (under about 60A total) to a service of 400A or larger, the math usually works without a study — the load is small enough that NEC's conservative calculation still leaves headroom. Same for adding a single DC fast charger to a service of 1200A or larger. Everything in between deserves the two weeks of metering. The study cost is modest compared to discovering mid-install that you need a service entrance upgrade — it's the cheapest insurance against a budget surprise we know of.

Managed charging changes the math

Networked chargers (ChargePoint, Tesla, ABB, Blink) support load-management — they can throttle their output collectively to never exceed a configured ceiling. For a retail center adding twelve Level 2 chargers totaling well over 100A nameplate, configuring them to share a much smaller circuit gives you twelve chargers behaving like the smaller circuit from the building's perspective. They charge slower at peak, faster at off-peak. For overnight workplace and multifamily, this is the right answer — and it often turns 'we need an upgrade' into 'we don't.'

Don't bid EV install off panel schedules. Spend $1,500 on a two-week demand study, look at the load profile, then decide between direct install, subpanel split, managed-charging throttling, or service upgrade. The study pays for itself the first time it saves you a guess that would have been wrong.