G100 import limitation for EV charging hubs and BESS

Export limitation is the familiar half of EREC G100: the distribution network operator (DNO) caps what a solar or storage site may send to the grid — the Maximum Export Limit (MEL) — and a scheme holds export inside it. Import limitation is the other half, and the standard covers it in full. Its title is Technical Requirements for Customers' Export and Import Limitation Schemes, and import schemes commissioned from 1 May 2023 fall under Issue 2. An import scheme holds what the site draws at or below the Maximum Import Limit (MIL).

New loads are arriving on supplies sized for something smaller. DC charging hubs are the clearest case: by September 2026 Zapmap counted more than a thousand public charging hubs in the UK — sites with eight or more rapid or ultra-rapid chargers. Batteries that charge from the grid and heat pumps replacing gas plant do the same. In December 2024 the government named energisation delays as a barrier to the charging rollout, and the National Audit Office found planning and grid barriers were slowing it.

Your connection agreement usually states a Maximum Import Capacity (MIC) in kVA; some DNOs call it Available Supply Capacity or Authorised Capacity. G100 works in current: the MIL is the current, agreed with the DNO, that the scheme holds net import at or below at the connection point. The DNO agrees how the two relate for your site.

When the load you want to add would take the site past its agreed capacity, the DNO may offer reinforcement, a DNO-managed flexible or profiled connection, or — where it accepts one — a customer import limitation scheme that holds net import at an agreed limit while the site carries more installed load. Since the 2023 connection-charging reforms most demand customers no longer pay for wider network reinforcement, so in most cases the honest case for limitation is time and available capacity rather than a cheaper bill.

The scheme measures current and voltage at the point of supply — net import for the whole site rather than one circuit — and compares it with the MIL. In normal operation it throttles (modulates) the controllable devices behind it: charger power, battery charging, heating plant. Uncontrolled load carries on; what flexes is the load that can flex.

G100 allows brief, time-limited excursions (short overshoots of the limit while the scheme acts) and treats failure as a designed-for condition. Loss of measurement, communications or power puts the scheme in its fail-safe state, and repeated or prolonged excursions bring a lockout that needs a deliberate reset. Where the fail-safe is triggered by excess import, the standard is explicit that the scheme must not trip or constrain on-site generation: it sheds load — switches off or turns down chargers and heating — or sets it to a defined low-power state instead.

As with export, G100/2 doesn't force sophistication. A simple scheme that trips controllable load to protect the limit is fully compliant; a dynamic scheme holds charger or battery power back and lets the site keep running. Trip or trim: we engineer whichever the site justifies.

The ENICO G100 Controller is fully type-tested to EREC G100 Issue 2 Amendment 2 for export and import limitation, and listed on the ENA Type Test Register, ref. ENICT/19509/V1. It is supplied as a standalone panel or built into the switchgear it belongs with — a main switchboard, a PV distribution board or a control panel. The same controller, the same compliance pack and the same register reference as our export schemes.

The product page covers formats, control modes, interfaces and the compliance pack.

A hub's chargers rarely all run at full power together. The standard's own worked example is a supermarket with a 300 kW import limit that wants fifty 22 kW AC chargers — 1,100 kW in total. With a scheme modulating charger load it seeks a 650 kW limit, and the DNO accepts it without reinforcement. That is the ENA's illustration, not a promise about your site, and the DNO assesses what its network can accept in each case. DC rapid hubs on forecourts, depots and destination sites are the same problem at higher power.

Many chargers and charge-management systems share power between their own units. A G100 scheme can sit above that layer as the enforcement layer: measurement at the connection point rather than inside the charger, tamper-protected settings, fail-safe behaviour, and the ability to override a back-office controller as the site approaches the limit.

Many chargers offer a power-limit interface. Control of charger power is engineered to the interface your equipment provides, confirmed at quotation.

G100 treats a battery in import mode as load. A BESS charging from the grid competes with everything else on the site for the same import capacity, and a tariff or market signal that says "charge now, it's cheap" may not account for what the rest of the site is drawing. An import scheme measures it at the connection point, can override the dispatch, and holds charging back as net import approaches the MIL — releasing it as demand falls.

Where the battery sits beside solar, both halves of the standard apply: export held inside the MEL when the array and battery push power out, import inside the MIL when the battery is filling. G100 assumes a scheme controls both directions unless it is declared export-only or import-only, and one ENICO scheme manages both at the same site from the same point of supply.

G100 names heat pumps alongside EV charge points and storage as devices a scheme may control. For a site replacing gas plant with heat pumps or electric heating, the import capacity that was adequate for lighting and small power becomes the bottleneck. G100 only comes into play where the connected load could actually exceed the limit, so the first question is what's on the schedule and which of it can flex. Ask us about heating and other large loads on your site.

G100 has three forms. Form A describes the proposed scheme and goes in with the connection application: the requested import limit and the controlled and uncontrolled load behind it, storage included. Form B is the manufacturer's compliance verification. Form C (Appendix C) records installation and commissioning. Where a scheme is Fully Type Tested and registered, the register reference on Form C stands in for a separate Form B, and site testing reduces to the communications and power-supply fail-safe checks. The ENICO G100 Controller is type-tested for import as well as export, so an import scheme follows that route.

We confirm what the offer requires, engineer the scheme to match, supply the scheme documentation and Appendix C paperwork for your submission, and support on-site testing where the DNO chooses to attend. After acceptance the settings are sealed: the limit changes only with the DNO's agreement. Which route a DNO offers for a given site — a customer limitation scheme, a DNO-managed flexible connection, or reinforcement — is its call, so start from the connection offer and talk to us early.