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Chapter 82 of BS 7671, introduced by Amendment 2 in 2022, gives additional requirements, measures and recommendations for the design, erection and verification of low-voltage installations that include local production or storage of energy, so that they remain compatible with existing and future ways of delivering electricity both to equipment in the house and back to the public network. Installations in scope are designated prosumer electrical installations, or PEIs, and the chapter reaches into energy efficiency, the interface with the smart grid, management of consumption, management of renewable sources and energy storage.

For a household that matters in concrete ways. Energy can flow in either direction through parts of the installation, so protective devices have to be suitable for bidirectional flow and selectivity has to be considered across more than one source. Safety during a grid outage becomes a design decision rather than an accident. Load planning takes on a meaning it never had in a consumer-only house, including the idea of shedding non-essential loads in island mode, where the installation runs disconnected from the public network.

Amendment 4:2026, in effect from 15 April 2026, pushed further in the same direction: the IET's summary notes that Section 551, on low-voltage generating sets, was modified to require a suitable protective device where energy flow is bidirectional, and to prohibit connecting sources to the load side of an RCD in certain circumstances. If you are buying a multi-part system, ask which edition the design is to.

Generating equipment connected in parallel with the public low-voltage network is governed by two Energy Networks Association engineering recommendations, and which one applies is decided by a current, not a headline kilowatt figure. EREC G98 covers micro-generators with nominal currents up to and including 16 amps per phase - which the ENA's connection guides give as 3.68 kW on a single-phase supply and 11.04 kW on three phase. Anything above that falls under EREC G99.

The difference is the order of events, and it catches people out. Under G98 the arrangement is connect and notify: the equipment must be fully type tested, and the installer informs the distribution network operator, with the information set out in the installation document, within 28 days of the date of commissioning. Under G99 the application comes first, before anything is connected, and the ENA's Type A guide notes that the planned commissioning date on the application must be between 10 working days and three months from the date the application is submitted.

The practical consequence for a whole-house system is that sizing decisions have a regulatory edge to them. A single-phase house adding an array plus a battery inverter can cross the 16 amps per phase line without anybody framing it as a decision, and the discovery that an application was needed beforehand is much worse than the conversation about it during design. Ask the installer, in writing, which recommendation the system falls under, who is notifying, and when.

Doing everything in one project is cheaper per component and produces one coherent design. There is a single set of scaffolding, one consumer unit alteration, one commissioning visit, one notification, and one party responsible when something does not behave. Chapter 82's concerns - bidirectional flow, selectivity across sources, behaviour in island mode - are far easier to satisfy when one designer has the whole picture.

Phasing is often the realistic choice anyway, and it works if the first phase is designed for what follows. That means specifying the inverter with the later battery in mind, leaving consumer unit capacity and physical space, running cable routes while access is open, and recording the supply arrangement and the notification position. The expensive version of phasing is the one where each phase is bought from a different installer against a different assumption, and the third one discovers the first two are incompatible.

There is a paperwork argument for coherence too. When solar, storage and a charge point come from three suppliers, three sets of certificates exist and none of them describes the installation as a whole. A future condition report, a house sale, or a fault that only appears when two of the three are active all become harder than they need to be.

The commonest failure is not electrical at all: it is that the pieces do not talk to each other. A battery that cannot see the solar inverter, a charge point that cannot see the battery, and a tariff optimiser that cannot see either will each behave sensibly on its own and stupidly together - exporting cheaply while importing expensively, charging the car from the grid at peak while the battery sits full. Nothing has failed; nothing was integrated.

The second is protection. A circuit that can be energised from two directions needs devices suitable for that, which is exactly what the changes to Section 551 in Amendment 4:2026 address. Retrofitting a second source onto an installation designed around a single one is where discrimination gets lost and where an inspector's eyebrows go up.

The third is the assumption about power cuts. Most grid-connected systems disconnect when the grid goes down, and a homeowner who assumed their battery would keep the lights on discovers otherwise in the first outage. Running in island mode is a deliberate design with its own requirements, including planning which loads get shed, and it has to be specified and paid for rather than hoped for.

The components are only part of it. The larger variables are the state of the existing installation - board capacity, earthing, cable routes, whether a supply upgrade is involved - and the ambition of the control layer, since a system that merely stores what the roof makes is far simpler than one that trades against a time-of-use tariff and keeps essential circuits alive in an outage. Whether the design crosses the 16 amps per phase line into G99 territory affects the programme as well as the cost, because an application comes before connection rather than after. Comparing quotations means comparing the design assumptions, not the size of the battery.

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