What is EREC G100?
As the UK transitions to commercial EV fleets, industrial heat pumps, and battery storage, the capacity of the existing connection is often the deciding factor. When a site's new electrical demand would exceed its existing connection, the Distribution Network Operator (DNO) has to assess whether the network can take it, which can mean waiting for reinforcement or a supply upgrade.
Engineering Recommendation (EREC) G100 offers another option. Published by the Energy Networks Association (ENA), it sets out the technical requirements for Customer Limitation Schemes (CLS). With the DNO's agreement, a site can connect equipment whose combined rating is above its agreed import limit, provided a scheme monitors total import and reduces the managed load to keep within the limit agreed with the DNO. Short excursions are permitted within set times, and the scheme must move to a fail-safe state if it fails.
Import vs. Export Limitation
Every commercial connection in the UK has two hard limits defined by the local DNO. The current edition, ENA EREC G100 Issue 2 Amendment 2 (April 2023), covers limitation schemes based on the direction of power flow:
- Active Load Management (ALM): Highly relevant for EV chargers. If total site demand approaches the import limit agreed with the DNO (often called the Maximum Import Capacity), the ALM system turns the chargers down to keep within it.
- Export Limitation: Crucial for Solar PV. If a solar array generates more power than the site is allowed to push back into the grid, the scheme curtails the inverters' output to keep export within the limit in the Connection Agreement, within the times G100 sets.
The 1-Minute and 5-Second Rules
A G100 scheme is usually a DNO application, unless the scheme holds the property at 60 A or less, in which case one new EV charger or heat pump can usually be connected and notified. The DNO assesses a G100 application using Form A, the manufacturer's type-test evidence (Form B or an ENA Type Test Register reference) and, after commissioning, the site test record (Form C). By default, if site demand goes over the agreed limit, the scheme must bring it back within the limit within 1 minute (3 minutes is allowed only for certain slow-acting technology notified to the DNO). Separately, if the scheme detects a failure, such as a communication or measurement fault (for example, a cut or damaged communication or CT cable, or a meter losing power) or an internal fault in the controller, it must move to its predefined fail-safe state within 5 seconds of detecting the failure.
After a fail-safe trip caused by an internal fault or by repeated or long excursions above the limit (G100 clause 4.5.1.3): non-domestic sites cannot be reset for 4 hours; domestic sites get 3 resets in any 30 days, then stay locked out until investigated. Trips caused only by a communication or CT fault can be reset once it is restored (clause 4.5.2.2).
Automate Your G100 Reports
A G100 scheme is usually an application, unless it holds the property at 60 A or less. Either way, it needs clear figures: the import limit, the existing demand, the new load and how much of it the scheme manages.
Gridcap works out those figures for your site and sets out the G100 requirements your chosen scheme must meet, as supporting information for your DNO application. It does not replace the DNO's assessment or the manufacturer's type-test evidence.
Source: ENA EREC G100 Issue 2 Amendment 2 (April 2023), Customer Limitation Schemes. This page is a summary; always check the full document and your DNO's requirements.