“We need a new connection from the DNO” is the most expensive sentence a fleet manager will hear, and a lot of the time it’s wrong. Modern dynamic load balancing lets a typical Leeds depot run 12+ EV sockets on the existing supply, without a new connection and without the 18-month wait. Here’s how the maths actually works.
Why the DNO-upgrade reflex is usually premature
Most quote requests start the same way: “We’ve got 20 vans to electrify, we’ll need an upgraded supply.” The reasoning sounds right — 20 × 7kW = 140kW, well above the 100A single-phase supply most depots have. The flaw in the reasoning is that vans don’t all charge at once, at full power, for the full window.
Real depot charging profiles look like this:
- Vans return between 17:00 and 19:00, not in a single wave.
- Most arrive with 30–60% state of charge, not empty.
- Charging window is typically 12 hours (overnight) for a 7am departure.
- A 7kW socket charging a 50kWh battery from 50% to 100% needs about 3.5 hours.
The supply isn’t sized for the peak of 20 × 7kW — it’s sized for the actual simultaneous draw across the charging window.
How dynamic load balancing works
Dynamic load balancing means the charger array shares the available supply intelligently:
- A current-transformer (CT) clamp measures the live draw on the incoming supply.
- The controller knows the headroom available — total supply minus building load minus a safety margin.
- That headroom is distributed across the active sockets, in real time.
- If a fast-charge spike happens elsewhere on the site, the EV sockets back off automatically.
The net effect: 12 sockets on a 100A single-phase supply can deliver a full overnight charge to 12 vans, with no supply upgrade required.
Worked example — 12 sockets on a 100A supply
A real-world depot scenario, sanitised:
- Incoming supply: 100A single-phase (24kVA gross capacity).
- Building base load overnight: 4kVA.
- Safety margin: 4kVA reserved.
- Available for EV charging: ~16kVA = 64A.
- 12 vans, each needing 25–35kWh added overnight.
- Total energy to deliver: 360kWh over 12 hours = 30kW average draw.
The average overnight draw (~30kW) exceeds the 16kVA headroom — so a smart array sequences charging, prioritising vans on lowest charge first, and clears the lot before the morning departure. No DNO upgrade, no 18-month wait, no £40k+ supply cost.
Hardware that plays nicely
The hardware question becomes critical at fleet scale. The shortlist:
- OCPP 1.6/2.0.1 compliance: Non-negotiable. Lets the depot controller speak to every socket regardless of manufacturer.
- Native load-balancing support: Some chargers support array-wide balancing natively; others need a third-party controller.
- Tariff-aware scheduling: Off-peak charging windows reduce the per-kWh cost without manual intervention.
- API for fleet-management integration: Telematics platforms can read state-of-charge and push schedules.
Zappi, Ohme and Andersen all hit the OCPP and load-balancing requirements at depot scale; the choice comes down to tariff integration and architectural preference.
When you do need the DNO call
Dynamic load balancing isn’t infinite. The genuine DNO-upgrade cases:
- 20+ sockets on a small commercial supply (<60kVA).
- Mixed-use site with heavy daytime industrial load and no overnight headroom.
- Fast-charging (50kW+) requirements alongside overnight 7kW.
- Future-proofing for an EV-only fleet within 24 months.
A site survey establishes which side of the line the depot sits on. Often it’s not the side the spec sheet suggests.
What to do next
If you’re scoping depot EV charging for a Leeds-area fleet and the existing quote includes a DNO supply upgrade, JP Electrical & EV Solutions will run a load survey first and confirm whether the upgrade is actually needed. OZEV-approved installer, NICEIC-approved, Part P compliant, Leeds-based team, available 24/7 for commissioning support.
Book a depot load survey or request a free, no-obligation quote via our workplace EV charging for fleets page, or read more about EV charger installation in Leeds.
FAQ
How many EV sockets can a typical 100A depot supply support?
With dynamic load balancing and an overnight charging window, 10–14 sockets is realistic for a typical Leeds light-commercial supply, assuming modest building load. A load survey confirms the number for your specific site.
Will load balancing slow down individual vehicle charging?
At peak times yes — each socket throttles to keep the total draw within headroom. The trade-off is overnight charging completes for all vehicles instead of the first three drawing full power and the rest waiting.
What’s the lead time for a depot install vs a DNO upgrade?
A load-balanced install on existing supply runs 4–8 weeks in Leeds. A DNO supply upgrade typically runs 12–18 months. The cost difference is similar — tens of thousands either way.