BS 7671 Guide · Section 8
EV charging, solar PV, batteries and heat pumps
Low-carbon kit turns a simple one-way supply into a busy two-way system. Here is what BS 7671:2018+A4:2026 expects when you add a charger, panels, a battery or a heat pump, and what to check before you start.
Start with the supply, not the kit
Every one of these jobs adds load, adds a source, or both. Before you quote, work out the new maximum demand and compare it with the cut-out fuse, tails and consumer unit. Regulation 132.16 won’t let you add to an installation unless the existing equipment, including the distributor’s, can take it.
Don’t apply diversity to a heat pump or charge point. Both run flat out for hours, often together on a cold evening. If the numbers don’t fit, the options are a supply upgrade or load management that genuinely limits demand.
Regulation references: 132.16, 311.1, 433.1
EV charging: Section 722
A circuit of its own
Each charge point needs its own dedicated final circuit. You can’t use diversity on a final circuit serving a charger, because the design assumes it draws its full rated current. Diversity is allowed on a distribution circuit feeding several chargers, but only where load control is fitted to hold total demand down.
RCDs and DC faults
Each charging point must have its own RCD with a rated residual operating current of no more than 30 mA. Type AC isn’t acceptable. The RCD can sit in the board or inside the charger, so read the data sheet before you buy a board-mounted device you don’t need.
A vehicle’s onboard charger can leak smooth DC fault current, which can stop an ordinary RCD tripping. So you also need DC fault protection, either:
- a Type B RCD, or
- a Type A or Type F RCD together with a residual direct current detecting device (RDC-DD) to BS IEC 62955, which is usually built into the charger.
Check upstream too. Under Regulation 531.3.3, DC leakage passed by a downstream device must not blind the RCD above it: no Type AC or Type A above a Type B, for example. If the board has a Type AC main RCD, feed the charger from outside it.
PME and the open-PEN problem
On PME, neutral and earth share one conductor in the network. If that PEN breaks, exposed metalwork can rise towards line voltage. A car on wet ground outside, with someone touching the bodywork, is the worst case.
So Regulation 722.411.4.1 says a PME earthing facility must not be used for a charge point that serves, or could reasonably serve, a vehicle outdoors unless one of these measures is used:
| Option | Comment cela fonctionne-t-il ? | Points to watch |
|---|---|---|
| Extra earth electrode | An installation electrode is connected to the MET, with a resistance low enough to hold the MET within 70 V of true earth if the PEN opens. | Needs a calculation (see the annex to Section 722) and an electrode that can actually achieve it. Often impractical on a typical house load. |
| Open-PEN device (70 V) | Disconnects line, neutral and earth within 5 s if the protective conductor rises more than 70 V above true earth. | Needs an earth reference: an electrode or a reference derived from three phases. |
| Open-PEN device (voltage window) | Disconnects all conductors, earth included, within 5 s if line-neutral voltage at the charger goes above 253 V or below 207 V. | Most common in domestic chargers. Must provide isolation and not reset until voltage is back in range. |
| Equivalent device | Any other method that gives at least the same level of safety. | Get the manufacturer’s evidence in writing. |
The older balanced three-phase option was deleted by A2, so don’t rely on it. The other route is not to use the PME earth for the charger at all: make the charge point circuit TT, with its own electrode and RCD fault protection, and keep that electrode clear of buried metal tied to the PME earth. Check the list of options in the current edition before you design.
AFDDs and load management
A4 adds Regulation 722.421.1.7.201. Circuits feeding EV charging equipment built to the BS EN 61851 series, with sockets or connectors to BS EN IEC 62196-2, don’t need an AFDD. That applies even in buildings where 421.1.7 would otherwise require one, such as HMOs or high-rise residential blocks.
Many chargers read whole-house current through a CT clamp and throttle back to stay under the fuse rating. That’s a legitimate way onto a tight supply. Record the setting, test it, and tell the DNO.
Regulation references: 722.411.4.1, 722.421.1.7.201, 722.531.3.101, 531.3.3
Solar PV: Section 712
The biggest difference with PV is that you can’t switch the DC side off. Panels make voltage whenever there is daylight, so treat the array cabling as live at all times.
- Isolation: provide it on both the DC and AC sides of the inverter. If the DC switch is built in, check its rating against the string.
- DC shock protection: string fault currents are too small to trip overcurrent devices, so double or reinforced insulation is the normal measure.
- AC connection: a dedicated circuit, sized from the inverter’s maximum AC output current.
- RCD type: Type B, unless the inverter gives at least simple separation between DC and AC, or its manufacturer says Type B isn’t needed.
- Surge protection: if Section 443 calls for SPDs on the AC side, protect the DC side too.
- Labels: dual-supply warnings at the origin, meter, consumer unit and every isolation point. The main switch no longer makes the installation dead.
For more on surge risk assessment, see Fire, arc faults and surge protection.
Regulation references: 712.537, 712.443, 712.534, 514.15.1
Batteries: new Chapter 57
A4 adds Chapter 57 for stationary secondary batteries used to store energy and supply an installation. Its scope excludes batteries inside products that have their own safety standard, such as a plug-in UPS. It also excludes central battery systems, fire alarm systems to BS 5839 and emergency lighting to BS 5266.
It covers selection of the battery, the power conversion equipment (PCE, usually the inverter) and the electrical energy management system (EEMS). It also covers earthing, shock protection including RCD-based automatic disconnection, fault protection on the DC side (where battery fault currents can be very high), isolation for maintenance, and warning notices.
Batteries in homes
In dwellings, A4 points you to PAS 63100 for location and fire safety: keep batteries out of rooms where people sleep, escape routes, lofts and voids, and provide fire detection where they sit. Elsewhere, location follows the premises’ fire risk assessment.
For the RCD in front of the battery PCE, take the same approach as PV: plan on Type B unless the PCE gives at least simple separation between its AC and DC sides, or its manufacturer says Type B isn’t needed. Confirm against Chapter 57 and the PCE instructions, and keep the manufacturer’s statement on file.
Regulation references: Chapter 57, 110.1.1
More than one source: Regulation 551.7
With PV, a battery or a vehicle-to-grid charger, current reaches the consumer unit from more than one direction. A4 redrafted Regulation 551.7 to deal with this.
- Batteries are generators. Regulation 551.7.2.1 treats a stationary battery as a generating set, not a load.
- Bidirectional devices. Where energy can flow both ways through a protective device, it must suit that (551.7.1 and 530.3.201). Devices marked “line/load”, “in/out” or with arrows are unidirectional and may not protect properly fed backwards.
- RCDs and sources. 551.7.1 now restricts connecting a source on the load side of an RCD in certain conditions. Read them before putting an inverter downstream of a shared RCD.
- Consumer unit rating. Regulation 551.7.2.2 makes you show the assembly can carry grid and generator current together. The simplest route is rating it for the sum: a 100 A supply plus a 16 A inverter means a 116 A board, unless another permitted route such as load limiting applies.
The prosumer chapter (Chapter 82, added in Amendment 2) sets out wider design considerations for installations that both make and use electricity, including load shifting, island operation and energy management. The IET’s Guide to Prosumer Electrical Installations expands on it.
Regulation references: 530.3.201, 551.7.1, 551.7.2.1, 551.7.2.2
Heat pumps
BS 7671 has no special section for heat pumps. They are fixed loads under the general rules, so the work is in the design:
- Size the circuit from the manufacturer’s maximum running current, not the heat output.
- Add any immersion or backup heater to maximum demand. It may run alongside the compressor.
- Fit the local isolator the manufacturer specifies, and pick a device curve that rides through compressor start-up.
Telling the network operator
The DNO needs to know about every heat pump, charge point and generator. The Energy Networks Association runs a shared process for heat pumps and EV chargers:
- Connect and notify: for a single new heat pump or charger, where the cut-out is in good order and its rating is known, the supply isn’t looped, and maximum demand stays below the cut-out rating and within the published limits (broadly 60 A per phase). A heat pump also needs a total system demand of 32 A or less and a connect-and-notify listing in the ENA heat pump database. Notify within 28 days.
- Apply to connect: anything outside those limits needs DNO approval before you connect.
- Generation and storage: type-tested inverters up to 16 A per phase connect under EREC G98 with notification after commissioning. Larger systems need G99 approval first. G100 covers export-limiting schemes where a battery or inverter is set to cap what goes back to the grid.
Criteria and forms change, so check the current ENA and DNO versions on every job.
Related: Protection against electric shock · Earthing and bonding · Inspection and testing
Important. This guide is written by Tradefox to help qualified electricians understand BS 7671:2018+A4:2026. It is a plain-English summary for learning and reference only. It is not the standard, it does not reproduce it, and it is not professional advice. Always work to the current edition of BS 7671, the IET guidance notes, manufacturers’ instructions, Building Regulations and your scheme provider’s requirements. Electrical work must be carried out by a competent person.
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