Section 712 — Prosumer’s LV Installations under A4:2026 — Battery, Solar PV & Microgeneration

The term "prosumer" — producer and consumer combined — entered the UK Wiring Regulations vocabulary formally with Section 826 of BS 7671 (definitions and energy-related terminology) and was given dedicated technical treatment in Section 712. A prosumer’s installation is a low-voltage electrical installation that both draws energy from the public distribution network and generates, stores or exports energy back. The classic 2026 example is a household with rooftop solar PV, a battery energy storage system, an EV charge point and a smart meter — all behind one cut-out and one earthing arrangement.

Before A4:2026, the relevant regulations were spread across Section 712 (solar photovoltaic power supply systems), the now-superseded Section 551 (low-voltage generating sets), and a small set of regulations on energy efficiency in Section 818. A4:2026 consolidated and substantially expanded Section 712 to deal with the reality that solar, battery and EV are routinely installed together and interact electrically.

For the broader prosumer concept, see the prosumer’s low-voltage electrical installation guide. This page is the deep dive on Section 712 itself.

Amendment 4, published on 15 April 2026 and in force from that date for new installations, made Section 712 one of the most substantially rewritten parts of the 18th Edition. The previous section dealt principally with solar PV; the amended section deals with the whole prosumer installation — generation, storage, export, islanded operation and interaction with the public supply.

1. Scope broadened beyond solar PV to cover any prosumer’s LV installation, including battery energy storage systems, small-scale combined heat and power, and microwind. Section 712 is now the single section for the prosumer’s LV side.
2. New requirements for battery energy storage systems (BESS), including selection of the inverter/charger, AC vs DC coupling, battery enclosure ventilation, and isolation arrangements specific to the battery DC side.
3. Expanded isolation requirements — isolators must be provided on each energy source so that the rest of the installation can be made dead independently. A solar isolator alone is no longer sufficient on a combined PV + battery installation.
4. Updated earthing arrangements for prosumer installations in TN-C-S systems, with explicit treatment of the case where the installation can operate islanded (disconnected from the public supply) and must establish its own earthing reference.
5. Cross-reference to Engineering Recommendation G98 and G99 made explicit. The Section 712 regulations now point directly to the ENA documents for grid-connection notification, Loss of Mains protection settings and anti-islanding behaviour.
6. New labelling and identification regulations — every prosumer installation must carry warning labels at the origin, at each isolator, and at the meter, identifying the presence of additional sources of supply.
7. New entries on the Schedule of Test Results columns — commissioning of a prosumer installation now requires recording the inverter make/model/firmware, the anti-islanding test result, the DC isolation insulation resistance, and the battery isolation verification.

A battery energy storage system is an assembly of electrochemical batteries, a battery management system, an inverter/charger, isolation, protection and monitoring — installed as a single functional unit on the prosumer’s LV installation. The Section 712 requirements sit alongside the product standards (IEC 62933 / BS EN 62909 series) and, for MCS-certified installs, MCS 020.

A battery can be connected to a solar PV array on the AC side of the PV inverter or on the DC side, sharing the DC bus. The choice has direct consequences for the Section 712 wiring requirements, for isolation, for efficiency and for behaviour on loss of supply.

Whichever topology is selected, Section 712.531 requires a dedicated isolator on each energy source — PV array, battery DC, and the AC connection to the consumer unit. The aim is that any one source can be isolated for maintenance without taking the rest of the installation offline, and that on supply failure the installation can be made completely dead from a single, clearly labelled, accessible location.

Section 712.531 sets out the isolation requirements for prosumer installations. Because energy can flow from more than one source, the standard single point of isolation at the consumer unit is not sufficient. Each generator and storage device must be capable of being isolated independently, and the whole installation must be capable of being made dead from a clearly identified location.

1. DC isolator on the PV array side — lockable, located adjacent to the inverter, rated for the PV array open-circuit voltage and short-circuit current at the design ambient temperature. Required under Section 712.531 and Appendix 4 derating.
2. AC isolator on the PV inverter output — lockable, located adjacent to the inverter, rated for the inverter’s maximum continuous output current.
3. DC isolator on the battery side — lockable, located within sight of the battery enclosure, rated for the battery system voltage and the maximum charge/discharge current.
4. AC isolator on the battery inverter output (AC-coupled topology) — separate from the PV inverter isolator, with its own dedicated overcurrent device on the consumer unit.
5. Main switch at the consumer unit — the primary point of isolation for the public supply, with appropriate warning that other sources of supply exist on the installation.
6. Single point of isolation for emergency — the prosumer installation must include a clearly identified, accessible emergency isolation arrangement that disconnects all sources simultaneously. This is typically the inverter’s integrated shutdown function, with a backup AC + DC isolation sequence documented in the user manual handed to the householder.

Most UK domestic supplies are TN-C-S (PME, with PNB now a recognised variant under A4:2026). The earthing of a prosumer installation must deal with two scenarios: grid-connected (the supply earth available via the combined neutral-and-earth) and islanded (supply lost, anti-islanding triggered, but the inverter is still energising local loads from the battery).

BS 7671 governs the prosumer’s side of the meter. The interface with the public distribution network is governed by Engineering Recommendation G98 and G99, issued by the Energy Networks Association (ENA). Any installer commissioning a prosumer installation must engage with one or the other — they are not optional. Section 712 of BS 7671:2018+A4:2026 cross-references them explicitly.

1. G98 — single-phase generation up to 16 A per phase (~3.68 kW per phase). "Connect and notify" — commission and energise, then notify the DNO within 28 days. Used for most domestic PV and small battery systems.
2. G99 — anything larger (single-phase > 16 A, all three-phase, multiple sources cumulatively > 16 A per phase). "Apply and connect" — apply to the DNO, receive a connection offer, accept it; only then energise.
3. Type-tested equipment — inverters used under G98/G99 must be type-tested and listed on the ENA Type Test Register. Off-register inverters cannot be used.
4. Loss of Mains protection — G98/G99 specify the LoM method (ROCOF or vector shift, depending on inverter age and DNO requirement), detection time and auto-reconnect delay.
5. Anti-islanding test — commissioning includes proving the LoM function by simulating grid loss. Inverter must disconnect within the specified time and must not reconnect until the grid is stable for the specified delay.
6. Witness testing — G99 installations above certain thresholds require DNO witness testing before energisation.

The DNO owns the local distribution network — UK Power Networks, Northern Powergrid, SP Energy Networks, SSEN, National Grid Electricity Distribution and Electricity North West cover GB between them. Notification is via the ENA’s Connect Direct service or the DNO’s connections portal.

1. G98 — commission, then submit the G98 document via the ENA Connect Direct portal within 28 days. The form captures property, installer, inverter make/model/firmware, type-test reference, rated output and LoM settings. No prior DNO consent.
2. G99 — submit the application before installation. The DNO assesses network capacity and issues a connection offer (which may impose curtailment, witness testing or upgrade contributions). Only after acceptance can the installation be energised.
3. Witness testing — where required, the installer arranges a DNO engineer to witness anti-islanding, ROCOF and other functional tests at commissioning. The DNO signs off and issues the connection agreement.
4. Connection agreement — once notification is complete (G98) or witness testing is passed (G99), the DNO issues the connection agreement permitting ongoing export.
5. Notification timeline — G98 is within 28 days post-commissioning but remains the installer’s responsibility. Failing to notify breaches the Distribution Connection and Use of System Agreement (DCUSA). G99 lead times can be 8–12 weeks.

Solar PV on the roof, battery in the garage, EV charge point on the driveway — the defining domestic install of 2026. Section 712 of BS 7671:2018+A4:2026 explicitly recognises this combination and sets out how the design must handle the interaction.

Loss of Mains (LoM) protection detects when the public supply has failed and disconnects the inverter from the AC bus to prevent islanding — the dangerous condition where the inverter continues to energise a section of the network after the DNO has switched it off. Without LoM, a DNO engineer working on a "dead" network could be electrocuted by a prosumer’s inverter still pushing voltage onto the local cable.

The standard Schedule of Inspections and Schedule of Test Results (Appendix 6) is the starting point for any prosumer installation, but is not sufficient on its own. A4:2026 added prosumer-specific items, and the EIC / EICR model forms have been updated to capture them.

1. Pre-commissioning visual inspection — confirm labels at consumer unit, meter, inverters, isolators and battery enclosure; confirm cable routes, mechanical protection, DC/AC segregation, enclosure ventilation and fire separation.
2. DC side insulation resistance — PV array IR to earth, before and after exposure to sunlight, per inverter manufacturer procedure. Battery DC side IR verified per manufacturer guidance; do not megger across the battery itself.
3. AC side insulation resistance — inverter disconnected for IR testing of AC final circuits, then reconnected and the AC circuit tested as a complete installation.
4. Continuity and earth fault loop impedance — measured at the furthest point of each circuit including the backup load panel. Zs must satisfy Section 712.411 ADS in both grid-connected and island modes.
5. RCD testing — each RCD verified to the required disconnection time at 1× and 5× IΔn. Type-A or Type-F as required for inverter-fed circuits with DC components.
6. Anti-islanding test — simulate grid loss with the inverter exporting; verify disconnection within the specified time; restore grid; verify the reconnect delay.
7. Inverter shutdown test — verify the documented emergency isolation sequence results in zero voltage at the load side within the inverter’s discharge time.
8. Functional check — verify the inverter starts, exports, throttles to CT clamp signal, charges/discharges the battery, and (if applicable) enters island mode on simulated grid loss.
9. Documentation — issue the EIC with the A4:2026 Section 712 columns completed, the G98 / G99 form, inverter type-test reference, LoM test result, battery user manual, and customer handover pack.