EV charger load headroom check
Existing demand vs what the supply can actually take. A quick sense-check before the site visit — not a substitute for the full maximum demand calculation.
The property's supply
Maximum demand before the charger — use the diversity estimator if you need it.
Headroom left on the supply
— comfortable headroom, but a full maximum demand check should still confirm it.
Sense-check only — not a design calculation. Doesn't replace a maximum demand assessment to BS 7671, DNO notification/approval, or the charger manufacturer's installation requirements.
Every domestic supply comes in through an intake fuse — 60A, 80A or 100A on most UK properties — and everything the property draws has to fit under that ceiling at once. An EV charger adds a big, sustained load on top of whatever's already there. Before it goes in, it's worth a quick check: does the existing demand plus the charger still leave room, or is the property already close to the limit?
How the check works
Enter the property's supply fuse rating, its existing assessed maximum demand (use the diversity estimator above if you need to work that out first), and the charger's rated current — typically 16A (3.6kW) or 32A (7.2kW) single-phase. The tool adds the charger to the existing demand and shows the headroom left under the fuse rating, both in amps and as a percentage.
Reading the verdict
Comfortable headroom (15% or more of the fuse rating spare) suggests the supply should take the extra load without drama, though a proper maximum demand calculation still needs doing before install. Tight headroom (under 15%) means the numbers technically fit but there's little margin — a load management (dynamic load balancing) device, which limits the charger's output when the rest of the property is drawing heavily, is worth strongly considering. Over capacity means the sums don't add up as things stand — that needs a load management device or a conversation with the DNO about a supply upgrade before anything is connected.
Notification still applies
Headroom is only one part of getting an EV charger connected correctly. In Great Britain, installers are required to notify the local Distribution Network Operator (DNO) about domestic EV charge point installations — some fall under a fast-track notification, others need approval before connection, depending on the property's supply and the charger's output. Since 2022, domestic and workplace chargers sold in GB have also had to meet smart charging requirements under the Electric Vehicles (Smart Charge Points) Regulations. Check current DNO and regulatory requirements for the specific installation — they're revised from time to time.
What this isn't
This is a headroom sense-check, not a design calculation. It doesn't replace a proper maximum demand assessment to BS 7671, a DNO notification or application, an earthing and PME assessment for the charge point, or the manufacturer's installation requirements. Use it to scope the conversation before a site visit, not to sign off an installation.
Seen enough? Claim your patch.
TradesInvo captures every enquiry, replies first, and runs it to a booked, quoted, paid job. Early access is five founder slots per postcode — check yours.