We're installing EV chargers.
Chargers are among the largest loads a commercial facility adds, and they run for hours at a time. Before anyone prices a new service, find out what the service you already have can carry.
How the Code Counts a Charger
A charger draws close to its full rating for as long as a vehicle is connected, so it is counted at that rating, and the code can size its circuit with a margin on top.
The figures assume a 125% margin on a 48 A charger. The margin that applies is set by your local code.
- The margin adds up
- With that margin, one 48 A charger needs 60 A of circuit capacity. Six of them need 360 A before anything else on the service is counted.
- Measured headroom is the starting point
- The chargers are added to what the service already carries at its busiest, established by the method your local code accepts for existing load. That existing figure decides whether the plan fits.
- Where the chargers land matters
- Chargers are often fed from a sub-panel. A utility bill sees the whole service and never one feeder, so a feeder question is answered by metering that feeder for 30 days.
Three Questions Before the First Charger
- 01
Can the service carry the chargers at their full rating, on top of what the facility already draws at its busiest?
- 02
Does the feeder or sub-panel they land on have room, measured on that feeder itself?
- 03
What will the new load do to the facility's peak demand, and to the demand charge that follows it?
What Answers It
Chargers on the main service
The Capacity Determination Report from 12 months of utility demand data, ready for the electrical plans.
Chargers on a sub-panel
30 days of loggers on the feeder the chargers will use, collected at the end of the window, then the determination.
Peak Determination
Your measured demand with realistic charging sessions laid over it, controlled and uncontrolled, stated as the new peak and what it does to the demand charge.
Load Management
Where your local code allows it, an automatic load management system can cap what chargers draw, and the installation is then calculated at the cap. That is a design decision for your charger installer, who specifies, installs and runs the system.
Wattif does not sell or operate load management. The determination tells you whether the service needs it.
Where This Comes Up
A grocery adding fast chargers for shoppers
The chargers go on the main service beside refrigeration that never switches off. The question is the service peak, read from a year of utility demand data.
A fleet depot charging vans overnight
The vans charge while the facility is closed, when the service is least loaded. The year of utility demand data shows whether that holds, and a sub-panel is metered where the chargers land on one.
An office garage with chargers on a sub-panel
The chargers share a feeder with garage ventilation and lighting. That feeder is metered for 30 days, because the bill cannot separate it.
Questions About Chargers
- How many chargers can my service take?
- That depends on what the service already carries at its busiest, and the report answers it for the charger model and count you give us.
- Do chargers that only run overnight still count?
- In the load calculation they count at their full rating, because a load calculation does not assume when they run unless a load management system caps them.
- Will you install the chargers?
- No. Wattif performs no electrical work. Your installer designs and installs the chargers, and the determination is written for their plans.