Smart Home and Consumer Unit Considerations: Dedicated Circuits for AV Equipment, EV and Battery Storage

Quick Answer: A smart home installation with AV equipment, EV charging, and battery storage requires careful consumer unit planning — typically a 17th or 18th Edition dual-RCD or RCBO-per-circuit consumer unit with at least 4–6 spare ways allocated during initial fit-out. EV chargers require a dedicated 32A circuit (7kW) or 16A circuit (3.6kW); battery storage systems (BESS) require a dedicated circuit plus isolation between grid, generation, and storage; and equipment racks benefit from a dedicated 20A circuit with the IT panel on a separate earth to reduce ground noise.

Summary

Consumer unit design is not typically in scope for a smart home installer who doesn't hold a Part P electrical registration. But understanding the electrical infrastructure that smart home systems depend on — and being able to identify when the existing consumer unit is inadequate — is essential for scoping projects accurately and avoiding callbacks caused by tripped circuits or interference.

The specific challenge with smart home installations is that modern properties accumulate electrical loads that were not anticipated when the consumer unit was installed: EV charger (7kW), battery storage system (potentially 5–10kW), AV equipment rack (1–3kW), home cinema projector and amplifiers (1–2kW), heat pump (4–12kW), and smart kitchen appliances. A consumer unit sized for a 2010 household doesn't have the ways or the main fuse rating for all of these simultaneously.

This article covers the consumer unit implications for smart home work. Actual consumer unit work must be carried out by a registered electrician with Part P competency — the information here is to help smart home specifiers ask the right questions.

Key Facts

• Consumer unit — the domestic equivalent of a switchboard; contains the main switch, RCDs or RCBOs, and individual MCBs for each circuit; must comply with BS 7671:2018+A2:2022 and be enclosed in non-combustible housing (metal enclosure required by 17th Edition Amendment 3 and 18th Edition)
• MCB (Miniature Circuit Breaker) — provides overcurrent protection for a circuit; rated in amps (6A, 10A, 16A, 20A, 32A, 40A, 50A, 63A); does NOT provide fault protection
• RCD (Residual Current Device) — detects earth leakage currents ≥30mA (Type AC) and disconnects within 40ms; protects against electric shock; most consumer units have 2 RCDs covering all circuits in two groups
• RCBO (Residual Current Circuit Breaker with Overcurrent protection) — combines MCB and RCD in one device; protects a single circuit independently; preferred for circuits where nuisance tripping of the RCD group is a problem (e.g. EV charger, freezer, AV rack)
• Type AC RCD — detects pure AC earth leakage; minimum standard; NOT suitable for EV charger circuits (DC fault component)
• Type A RCD — detects AC and pulsating DC leakage; required as minimum for EV charger circuits per BS 7671 Amendment 2 2022
• Type B RCD — detects AC, pulsating DC, and smooth DC leakage; required by some EV charger and battery storage manufacturers
• Consumer unit rating — main switch amperage (typically 100A for standard UK supply); must match the incoming DNO fuse rating; some properties have 60A or 80A main fuses — check before adding high-current loads
• Dedicated circuit — a separate circuit from the consumer unit to a specific load; prevents other loads affecting the circuit and allows fault isolation; recommended for EV, battery storage, AV racks, and cinema
• DNOQ (DNO Connection Quantity) — utility companies may limit EV charger and battery storage connection without prior approval for supplies over certain power thresholds; check with DNO before specifying EV or BESS installations
• G98/G99 — Engineering Recommendation G98 (micro-generation <16A/phase) and G99 (larger generation/storage); notification/approval process for battery storage and solar PV systems connecting to the grid
• Protective Multiple Earthing (PME) — the most common earth arrangement in UK domestic supplies; uses the combined neutral and earth (PEN conductor) of the DNO network; creates specific requirements for EV charger earthing

Quick Reference Table

Detailed Guidance

Dedicated Circuits for AV Equipment

High-quality AV equipment — particularly power amplifiers, AV receivers, and projectors — can draw significant inrush current at switch-on and have demanding continuous current requirements. More importantly, interference on a shared circuit (from washing machines, fridges, dimmer switches) can introduce audible hum or noise into audio systems.

Why a dedicated AV circuit?:

• Eliminates common-impedance coupling between AV equipment and other domestic loads
• Allows use of a power conditioner/line filter on the AV circuit to improve power quality
• RCBO protection means an AV circuit fault does not trip the whole ring main

AV equipment rack power planning: A typical AV rack containing: AV receiver (1000W peak), 2-channel power amplifier (500W peak), NAS (60W), media server (150W), router (30W), managed switch (100W) = approximately 1840W peak load. A 20A circuit (4600W at 230V nominal) provides substantial headroom.

IT ground / star earth: Some installers provide a star-point earth connection for AV rack components — all chassis connected to a single point connected to building earth. This reduces earth loops and associated hum. This is a supplementary bonding technique, not a replacement for the standard protective earthing required by BS 7671.

EV Charger Circuit Requirements

EV charging is the highest-current single new circuit that residential consumers add to their homes. The circuit requirements are:

32A dedicated radial circuit for a 7.2kW (32A) single-phase smart charger:

• Cable: 6mm² or 10mm² twin + earth (depending on run length and installation method); 6mm² rated 47A in free air, 32A clipped direct in conduit — verify with cable manufacturer's current-carrying capacity tables
• RCBO protection: Type A minimum; some EV charger manufacturers (Ohme, Zappi, Pod Point) specify Type B RCD — follow manufacturer instructions
• RCD protection: EV chargers produce DC fault currents that defeat standard Type AC RCDs; Type A is the minimum as per BS 7671 Amendment 2 2022 Appendix 15

PME earthing and EV charging: Under PME earthing (most UK domestic supplies), the combined neutral-earth conductor creates a risk that during a DNO neutral fault, the earth path at the EV charger could rise to hazardous voltages. BS 7671 Chapter 72 requires either:

1. An earth electrode at the EV charger location (TT arrangement for the charger circuit), OR
2. The charger has a device that disconnects if the N-E voltage exceeds 70V (some modern smart chargers incorporate this), OR
3. A PME disconnection device

In practice, most UK EV charger installations use an earth electrode approach: a copper earth rod driven adjacent to the charger, connected to the charger's PE terminal. The installed circuit remains PME-earthed at the consumer unit, with TT protection at the charger.

OZEV grant compliance: The UK Government's Electric Vehicle Homecharge Scheme (EVHS) — replaced by the EV Chargepoint Grant from 2023 — requires installation by an OZEV-approved installer. Approval requires NAPIT or NICEIC registration plus OZEV-specific training.

Battery Storage System (BESS) Circuit Requirements

Home battery storage systems (Tesla Powerwall, Givenergy, SolarEdge, Sonnen) are increasingly common alongside solar PV. The electrical connection requirements vary by system but generally:

For AC-coupled BESS (battery connects on the AC side):

• Dedicated consumer unit input/output point
• G98/G99 notification to the DNO before commissioning
• Over/under frequency and voltage ride-through settings configured to DNO specification
• Isolation from the grid during power outage (anti-islanding protection built into the inverter)
• Typically a 16A or 32A circuit from a dedicated RCBO in the consumer unit

For DC-coupled BESS (battery connects via DC to the solar PV inverter):

• Hybrid inverter handles the DC interface; AC side requirements as above
• The DC cable between battery and inverter must be rated for DC voltage and installed in separate conduit from AC cabling

Consumer unit impact: Adding a BESS alongside solar PV means the consumer unit potentially has two generation sources (PV and BESS discharging) in addition to the grid supply. The consumer unit must have appropriate bus bar ratings and the incoming meter may need upgrading to a smart import/export meter — coordinate with the DNO.

Smart Home Hub Circuit Requirements

The smart home control system — hubs, servers, NAS, routers, and network switches — should be on a circuit connected to a UPS. The UPS provides:

• Continued operation during brief power outages (10–20 minutes for a 1500VA UPS)
• Protection against voltage spikes and sags that can corrupt smart home hub configuration
• Clean sine wave output (for true online UPS) benefiting network and server equipment

A 10A radial circuit to the structured wiring cabinet with a 1500VA UPS is standard for a comprehensive smart home installation.

Frequently Asked Questions

Our existing consumer unit is full. Can we just add a secondary consumer unit?

Yes — a secondary consumer unit (sub-board) can be added, fed from the existing main consumer unit via a suitably rated cable. The secondary consumer unit requires its own main switch and RCD/RCBO protection. This approach is common for EV chargers and BESS installations where spare ways in the existing board are exhausted. All work must be carried out by a Part P registered electrician.

Does an EV charger affect the house's electricity meter?

Yes — all electricity drawn through an EV charger (and generated/stored by a BESS) passes through the DNO electricity meter. If the charger has its own smart meter for sub-metering, that is additional to the main meter. Smart chargers can communicate with time-of-use tariffs (Octopus Agile, Intelligent Octopus) to charge the vehicle during cheap overnight periods.

Does smart home equipment need surge protection?

It benefits from it. Mains voltage transients (from lightning, switching of nearby inductive loads, DNO switching) can damage sensitive electronics. A whole-home Type 1/2 SPD (Surge Protection Device) at the consumer unit, supplemented by Type 3 SPDs at the AV equipment rack, provides layered protection. The 18th Edition of BS 7671 made SPD assessment mandatory for new installations — the risk assessment must be documented by the installing electrician.

Regulations & Standards

• BS 7671:2018+A2:2022 (IET Wiring Regulations 18th Edition) — consumer unit specification, RCD types, EV charging (Chapter 72), BESS (Chapter 56), SPD assessment

• Building Regulations Part P — consumer unit work is notifiable; must be carried out by a Part P registered electrician or notified to Building Control

• Engineering Recommendation G98 — notification requirements for micro-generation systems (including BESS < 16A/phase)

• Engineering Recommendation G99 — approval requirements for larger generation and storage systems

• OZEV EV Chargepoint Grant Criteria — installer qualification requirements for EV charger grant eligibility

• IET — Wiring Regulations 18th Edition (EV Charging Guidance) — Chapter 72 guidance for EV charger circuit requirements

• OZEV — EV Chargepoint Grant — approved installer requirements and grant conditions

• Solar Energy UK — BESS Connection Guidance — G98/G99 process for battery storage systems

• ENA — Engineering Recommendation G98/G99 — generation and storage connection standards

• Part P implications for smart home work — when consumer unit changes become notifiable

• home networking and structured wiring cabinet — power requirements for the structured wiring cabinet

• multiroom audio installation — dedicated circuit planning for AV equipment rack

• home EV charger installation — detailed EV charger circuit requirements