BS 7671 Amendment 4: Residential Energy Efficiency

Amendment 4 introduces Chapter 81, bringing energy efficiency considerations into BS 7671 for the first time. For residential installations, this represents a philosophical shift — the wiring regulations now consider not just safety but also the energy performance of the electrical installation itself.

Chapter 81 does not mandate specific energy-saving measures for residential installations, but it establishes a framework of recommendations that designers should consider. The most impactful recommendation is circuit arrangement for energy monitoring. Chapter 81 suggests that new residential installations should arrange final circuits to facilitate energy monitoring — separating high-energy loads (EV chargers, heat pumps, electric showers, cookers) onto individual circuits that can be independently monitored.

This circuit arrangement recommendation aligns with the smart home trend and the forthcoming Ofgem half-hourly settlement regime. By separating high-energy loads, homeowners can use smart energy monitors and time-of-use tariffs to reduce costs and carbon emissions. While Chapter 81 frames this as a recommendation rather than a requirement, Building Regulations Part L may adopt it as mandatory in future revisions.

Sub-metering provisions are addressed for the first time. Chapter 81 recommends that new residential consumer units include provision for energy monitoring on major circuits. This may mean specifying consumer units with integrated CT (current transformer) mounting points, or leaving space for retrospective installation of energy monitoring devices.

EV and heat pump readiness features prominently. Chapter 81 recommends that new residential installations include pre-wired capacity for an EV charger (typically a 32A radial circuit) and a heat pump supply (circuit capacity depends on the heat pump rating, but a 40A supply is a reasonable default). These circuits may be terminated at an isolator rather than connected to equipment, but the cable and protective device should be installed during the initial fit-out to avoid disruptive retrofitting.

Power factor correction is mentioned for the first time in a residential context. While residential power factor has historically been ignored, the proliferation of switch-mode power supplies, LED drivers, and EV chargers means that residential power factor is deteriorating. Chapter 81 recommends that designers consider the power factor impact of the connected load when sizing the supply and protective devices.

ECalPro's Maximum Demand Calculator supports Chapter 81 energy efficiency assessments, including circuit arrangement analysis and EV/heat pump readiness calculations.