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

Quick Answer: A modern smart-home / AV install typically needs three or more dedicated circuits at the consumer unit: one for the AV / network rack (16A or 20A on a Type B RCBO with surge protective device), one or more for lighting control if separate from existing lighting circuits, and dedicated 32A/40A circuits for EV charger or battery storage. Consumer units installed since BS 7671:2018 must have RCD or RCBO protection on every final circuit and an SPD (surge protective device) under amendment A2:2022. Adding circuits typically requires consumer unit replacement if the existing unit is full or non-RCD.

Summary

The consumer unit (or "fuse box") is the heart of the home's electrical installation. For traditional homes built 20-30 years ago, the existing consumer unit may be a 6-way or 8-way unit with all circuits in use, no RCD protection beyond a single 30 mA RCD covering everything, and no surge protection. Adding the dedicated circuits a modern smart-home and AV install requires often means replacing the consumer unit — turning a smart-home project into a major electrical refurbishment.

This article covers what circuits are typically needed, how to specify the consumer unit upgrade, the regulatory implications under BS 7671:2018+A2:2022 and Part P, and the integration of EV charging and battery storage that has now become a near-mandatory part of high-end residential projects.

The goal is to help smart-home installers and electricians scope the consumer unit work correctly at the start of a project, rather than discovering mid-build that the existing unit can't accommodate the required circuits.

Key Facts

• BS 7671:2018+A2:2022 — current Wiring Regulations; mandates RCD/RCBO on all final circuits in dwellings, SPD on supply
• Consumer unit replacement — always notifiable under Part P
• RCD (Residual Current Device) — 30 mA Type AC, A or B
• RCBO (RCD + MCB combined) — preferred over single RCD for multiple circuits; fault on one circuit doesn't trip others
• MCB (Miniature Circuit Breaker) — overcurrent protection only; needs separate RCD upstream
• Type AC RCD — older standard; AC fault current only
• Type A RCD — current standard; AC + pulsed DC; required for many modern loads
• Type B RCD — sensitive DC fault detection; required for EV charging, PV, battery storage
• SPD (Surge Protective Device) — Class T2 mandatory in domestic CUs under A2:2022 amendment
• AFDD (Arc Fault Detection Device) — recommended for fire-risk locations; mandatory in some special premises
• Main switch — typically 100A or 125A double-pole isolator
• Tails — meter tails 25mm² minimum 16A; up to 6mm² for 60A or 100A
• PEN fault detection — required for EV chargers connected to PME supply per BS 7671 722.411.4.1
• DNO notification — G98 for ≤16A single-phase generation; G99 for >16A
• Earthing system — TN-C-S (PME most common in UK), TN-S, TT (with own earth electrode)
• CU position — domestic consumer units typically in cupboard, hallway or utility room
• Headroom — typical consumer unit needs 8-12 spare ways for new circuits (one EV charger + battery + 2-3 dedicated circuits)
• Dedicated AV rack circuit — typical 16A radial; allows isolation without affecting other rooms
• Surge protection on AV — secondary SPD at the rack also recommended

Quick Reference Table

Detailed Guidance

When the existing consumer unit must be replaced

The existing consumer unit must be replaced if any of the following:

• All ways used and new circuits required
• No RCD protection (older "split-load" or non-RCD units)
• Non-domestic-rated unit found in older properties
• Single 30 mA RCD on all final circuits (modern best practice is RCBO per circuit)
• Plastic enclosure where regulations now require metal (BS 7671:2018+A1:2018)
• Damage, corrosion, fault history

Replacement is fully notifiable under Part P. The Competent Persons Scheme (CPS) registered electrician issues an EIC after work and the scheme notifies Building Control automatically.

Specifying a new consumer unit

For a modern smart-home / AV / EV / battery installation in a typical UK 4-bed home, specify:

• Metal enclosure — BS EN 61439-3 compliant, IP30 minimum
• Main switch — 100A or 125A double-pole isolator (verify with DNO if approaching 100A demand)
• 18-24 ways — for headroom; underspecifying fills up after one extension
• RCBO per circuit — Type A on most, Type B on EV / inverter / battery circuits
• Class T2 SPD — surge protective device on incoming supply
• AFDD — recommended on bedroom and kitchen circuits (fire risk locations)
• Surge protection coordination — Class T2 in CU, optionally Class T3 at sensitive loads (AV rack)

Manufacturers commonly used in UK residential:

• Hager — Design 30 series; modular, well-supported
• Schneider Electric (MG) — Resi9, Easy9
• MK / Honeywell — Sentry
• Wylex — NM range
• Lewden / Crabtree — competitive value

Whichever manufacturer, ensure the CPS-registered electrician is familiar — terminal layouts and torque settings vary.

EV charger circuit

EV chargers of 7.4 kW (32A single phase) or 11 kW (16A three phase) require dedicated circuits. Key points:

• Cable size — 6mm² T+E for 32A on a typical 30m run; 10mm² for longer or higher current
• RCD type — Type B integral to charger (most modern Wallbox, Easee, Pod Point, MyEnergi units include this) OR Type B RCBO at CU
• PEN fault detection — required if supply is TN-C-S (PME) per BS 7671 Section 722
• DNO notification — G99 if charger >16A per phase (most home chargers fall under G98 only if ≤16A; verify)
• Smart Charge Points Regulations 2021 — requires smart functionality, default off-peak settings
• Earth electrode — installed at the EV outlet if supply earthing inadequate; alternative to PEN fault detection

Cable routing must avoid:

• Areas susceptible to mechanical damage (use SWA armoured cable underground)
• Cable sharing with high-current circuits (parallel runs for >5m can cause induction)
• Garage interior runs without mechanical protection (clip to wall, don't drape)

For an EV charger commissioning visit, the registered electrician or charger installer:

1. Verifies supply earthing system (PME, TN-S, TT)
2. Confirms RCD type (B integral or external)
3. Tests RCD trip times
4. Notifies DNO (G98/G99) with charger details
5. Issues EIC
6. Commissions charger with the manufacturer's app
7. Tests charging session

Battery storage / inverter

Battery and inverter installations are increasingly common alongside EV chargers, often as part of a solar PV install. Key considerations:

• Inverter type — string inverter for PV-only, hybrid inverter for PV + battery, AC-coupled battery for retrofit
• Inverter rating — domestic typically 3.6 kW (single-phase G98 limit) or up to 5 kW with ENA's Engineering Recommendation G98
• Battery sizing — typical 5-15 kWh; aligned with daily energy use
• Cable — 6 or 10mm² depending on rating
• Type B RCD — required as inverter introduces DC fault current potential
• Anti-islanding protection — inverter detects grid loss and disconnects (G98/G99 mandatory)
• DNO notification — G98 (≤16A per phase) or G99 (>16A); MCS-certified install for grant eligibility
• Battery enclosure — typically wall-mounted in garage / utility / outside; ventilation per BS EN 50272

For G98 installations the DNO is informed via the electrician's notification (within 28 days of commissioning). For G99 the DNO must approve before commissioning — adds 4-12 weeks lead time.

AV rack dedicated circuit

The AV / smart-home equipment rack benefits from a dedicated 16A circuit:

• Isolates electrical noise — switching loads (washing machine, kettle) on the same circuit cause hum and digital glitches in audio equipment
• Provides clean isolation — turn the rack off without affecting other circuits
• Allows secondary SPD — Class T3 device at the rack provides additional surge protection for sensitive equipment
• Future-proofs — equipment loads grow; 16A dedicated circuit handles 3.6 kW
• Reduces RCBO trip risk — fault in one device doesn't take down the entire rack

A typical AV/network/smart-home rack with:

• Network switch (PoE, 200W)
• Router / firewall (50W)
• AV streamer / amp (200W)
• NAS (50W)
• KVM and management (50W)

Total ~550W = 2.4A. 16A circuit gives 5x headroom. Connect rack via UPS for short outages.

Surge protection — what's actually needed

Under amendment A2:2022 of BS 7671:2018, all consumer units in dwellings must have:

• Class T2 SPD — protects against transient overvoltage (lightning indirect strikes, switching surges from grid)

Optional secondary protection:

• Class T3 SPD — installed near sensitive equipment (rack, computer, TV)
• Combined Class T2+T3 — single device covering both stages

The Class T2 SPD installed at the CU protects the building wiring from transients. A laptop charger, however, plugged in 30m of wiring away, may still see transients. Class T3 at the equipment provides the second line of defence for valuable electronics.

Integrating with smart-home systems

Modern consumer units can be IoT-integrated:

• Energy monitoring — devices like Shelly EM, Wallbox energy meters, Sense Home Energy Monitor
• Per-circuit metering — Shelly EM has clip-on CTs, gives per-circuit energy data
• Remote isolation — smart MCBs / breakers (Hager Resi9 with VLink) allow per-circuit remote control
• Fault notification — push notifications on RCD trips

This data feeds the smart home — enabling "if washing machine done, turn off" automation, energy budgeting, fault alerts. The hardware is fitted in or near the CU.

Working with electricians on smart-home projects

Smart-home installers without in-house Part P registration must coordinate with an electrician for any consumer unit work. Best practice:

• Engage the electrician at design stage, not at execution
• Provide a clear loading schedule (which circuits, what they feed, expected current)
• Discuss earthing system (PME confirmed?) early
• Coordinate cable routes to avoid disruption
• Schedule site visits — first fix (cable runs), second fix (CU and terminations), commissioning

Disputes on smart-home projects often arise because the electrician arrives and finds the CU is full, or the supply is inadequate, with no prior planning. A 30-minute pre-installation visit by the electrician saves days of rework.

Frequently Asked Questions

Do I need a new consumer unit just to add a smart home?

It depends on the existing unit's spare capacity and protection. If your unit has:

• 4+ spare ways
• 30 mA RCBOs per circuit
• Type A RCDs
• Metal enclosure
• Class T2 SPD

…then no, you can probably add new circuits without replacement. If any of the above is missing (and certainly if the unit is plastic-enclosed or has no RCDs), replacement is the right answer.

How big is the dedicated AV circuit really need to be?

For most domestic smart-home / AV racks, 16A is more than enough — total continuous load rarely exceeds 5A. The dedicated circuit is more about isolation and clean power than current capacity. For larger installs with multiple amplifiers, 20A may be specified.

Does my EV charger really need a Type B RCD?

Most modern EV chargers integrate Type B RCD detection within the charger itself, allowing a Type A or even Type AC RCD upstream. Older or simpler chargers without this feature need a Type B RCBO at the consumer unit. The supplier's installation manual is definitive — follow that, not generic guidance.

Why is surge protection mandatory now?

Amendment 2 (A2:2022) made SPD mandatory in domestic consumer units because lightning strikes and grid switching surges are increasingly damaging modern electronics. A typical surge can destroy a £2,000 TV or AV system. The £100-£200 cost of a Class T2 SPD pays for itself the first time it activates.

Can I add a new circuit without notifying Building Control?

No. Any new circuit added at the consumer unit is notifiable under Part P. Either: (1) the work is done by a CPS-registered electrician who self-certifies and the scheme notifies Building Control, or (2) the work is notified to Local Authority Building Control before starting and they inspect at completion.

Regulations & Standards

• BS 7671:2018+A2:2022 — Requirements for Electrical Installations (the IET Wiring Regulations)

• Building Regulations Part P — Notifiable electrical work

• BS EN 61439-3 — Low-voltage switchgear and controlgear assemblies; Part 3: Distribution boards

• BS EN 61009 (RCBO) — RCD/MCB combined devices

• BS EN 61008 (RCD) — Residual current operated circuit-breakers

• BS EN 60898 (MCB) — Circuit breakers for over-current protection

• BS EN 62305 series — Lightning protection (relevant for SPD coordination)

• G98 (≤16A) — ENA Engineering Recommendation for connection of small generators

• G99 (>16A) — ENA ER for larger generators

• Smart Charge Points Regulations 2021 — Statutory instrument; smart functionality for EV chargers

• The Electricity at Work Regulations 1989 — Statutory; safe electrical installation work

• BS 7671:2018+A2:2022 — IET Wiring Regulations

• Approved Document P — gov.uk

• Energy Networks Association G98 / G99 — DNO connection requirements

• OZEV EV Charger Grants — gov.uk EV grants

• Hager UK — Design 30 Consumer Units — Manufacturer technical guidance

• Schneider Electric Resi9 — Consumer unit product range

• part p implications smart home — Notifiability of consumer unit work

• smart home battery storage integration — Battery storage at CU

• smart lighting installation — Lighting circuit considerations

• smart heating controls — Boiler/heat pump circuits

• home networking for av — Dedicated rack circuit for network