Heat Pump Electrical Protection Requirements UK | RCD

🌡️ Heat Pumps · Type B RCD · BS 7671 · Inverter Protection

Heat Pump Electrical Protection Requirements UK

Heat pumps are not standard electrical loads. They use inverter-driven variable speed compressors that generate DC and high-frequency leakage currents that a standard Type A RCD cannot detect. Getting the protection right isn’t optional — it’s a BS 7671 requirement, and it requires specific devices that most electricians don’t routinely stock.

Covers: air source & ground source heat pumps · Type A vs Type B RCD · 20kHz protection · SPD requirements · BS 7671 compliance
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Direct Answer

Heat pumps require a Type B RCD (not Type A), which detects AC, pulsating DC, and smooth DC residual current. The inverter-driven compressor produces DC leakage that a Type A RCD is blind to. Where the inverter operates at frequencies above standard power frequency (common in modern high-efficiency units), a 20kHz Type B RCD is required. Both variants need a Type 2 SPD. EcoHarmony stocks pre-assembled heat pump consumer units with both Type B and 20kHz Type B options.

Type B RCD required Type A not sufficient 20kHz variant for VRF systems SPD required BS 7671 compliant Pre-assembled CUs available
🏠 Plain English — Why can’t I just use a normal RCD?

A standard Type A RCD detects two types of fault current: alternating (AC) and pulsating DC. It was designed for conventional electric loads — heaters, motors, lighting — that behave in predictable ways.

A heat pump is different. Its inverter converts AC power from the grid into variable-frequency AC to drive the compressor at different speeds. This conversion process introduces smooth DC leakage current as a by-product. Type A RCDs don’t detect smooth DC — that fault current passes straight through without tripping the device.

A Type B RCD adds smooth DC detection to its repertoire. It’s the same physical format as a Type A — it just detects more types of fault. That additional detection capability is what heat pump installations require under BS 7671.

Some modern high-efficiency heat pumps go further and operate their inverters at frequencies up to 20kHz (above the standard 50Hz power frequency). For these systems, an even more capable RCD — rated to 20kHz — is required. That’s what EcoHarmony’s 20kHz Type B consumer unit provides.

Why Heat Pumps Need Type B RCDs

Under BS 7671 Amendment 3 (2020) and subsequent guidance, equipment with inverter drives — which includes all modern heat pumps — must have RCD protection that is appropriate for the type of leakage current the equipment can produce.

RCD Type Detects AC faults Detects pulsating DC Detects smooth DC Suitable for heat pumps?
Type AC Yes No No No
Type A Yes Yes No No — misses smooth DC leakage
Type B Yes Yes Yes (up to 1kHz) Yes — for standard inverter heat pumps
Type B 20kHz Yes Yes Yes (up to 20kHz) Yes — for high-frequency inverter systems

Installing a heat pump with only a Type A RCD is a non-compliant installation

The smooth DC leakage from the heat pump inverter will pass through a Type A RCD without triggering it. If a genuine fault develops, the RCD may not trip — leaving the circuit unprotected. This is both a safety issue and a building regulations compliance failure.

Do You Need Standard Type B or 20kHz Type B?

This is the key specification question for heat pump installers and electricians, and the answer depends on the heat pump model.

Standard Type B RCD (up to 1kHz)

Covers the vast majority of air source and ground source heat pumps. The inverter operates at frequencies within the standard detection range. Suitable for most Vaillant, Daikin, Mitsubishi, Samsung, and similar residential heat pump models.

EcoHarmony product: Heat Pump Consumer Unit — Type B RCD + SPD + MCB — £135

20kHz Type B RCD

Required for variable refrigerant flow (VRF) systems, commercial heat pumps, and some high-efficiency residential units where the inverter switching frequency extends above 1kHz. Check the heat pump manufacturer’s electrical specification document for the stated inverter frequency range.

EcoHarmony product: WCED Heat Pump Protection CU — 20kHz Type B RCD + SPD — £235

How to check: The heat pump manufacturer’s installation manual will specify the type of RCD required. Look for wording like “Type B RCD required” or “frequency-sensitive RCD required”. If the manual specifies a Type B without frequency qualification, the standard Type B consumer unit (£135) is appropriate. If it specifies 20kHz or “high-frequency” RCD, use the 20kHz variant (£235).

SPD Requirements for Heat Pumps

Heat pumps contain sophisticated inverter electronics and control boards. These are significantly more vulnerable to transient overvoltages (lightning and switching surges) than simple resistive loads. BS 7671 Appendix 16 requires a Type 2 SPD where the risk assessment determines one is needed — for an outdoor heat pump unit, this is almost invariably the case.

Both EcoHarmony heat pump consumer units include a Type 2 SPD pre-wired and tested as part of the assembly. There is no need to source and specify an SPD separately.

Products for Heat Pump Installations

Standard heat pump · Type B RCD · £135

Heat Pump Consumer Unit — Type B RCD + SPD + MCB

Pre-assembled consumer unit for standard heat pump installations. Type B RCD (standard frequency) + Type 2 SPD + MCB protection. Covers the vast majority of residential air source and ground source heat pump models. BS 7671 compliant. Pre-wired, tested, and ready to install.

  • Type B RCD (standard frequency, up to 1kHz)
  • Type 2 SPD — pre-wired
  • MCB protection
  • BS 7671 compliant for inverter-driven heat pumps
  • Suitable for: most Vaillant, Daikin, Mitsubishi, Samsung residential models
Buy — £135.00 →
High-frequency inverter · 20kHz Type B RCD · £235

WCED Heat Pump Protection CU — 20kHz Type B RCD + SPD

Pre-assembled consumer unit for heat pumps with high-frequency inverters (VRF systems, commercial units, and high-efficiency residential models where the inverter operates above 1kHz). 20kHz Type B RCD + Type 2 SPD + main switch + MCBs. The comprehensive solution where the heat pump manufacturer specifies high-frequency RCD protection.

  • 20kHz Type B RCD — covers high-frequency leakage currents
  • Type 2 SPD — pre-wired
  • Main switch for isolation
  • MCB protection
  • Suitable for: VRF systems, commercial heat pumps, high-spec residential units
Buy — £235.00 →

Heat Pump + EV Charger on the Same Property

An increasingly common scenario: a homeowner installs both a heat pump and an EV charger. The protection requirements for each are different, and they share the incoming supply. Key considerations:

⚡

Separate circuits, separate protection

The heat pump and EV charger should be on separate dedicated circuits, each with appropriate protection. The Type B consumer unit for the heat pump is a separate installation from the WCED board for the EV charger.

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Load balancing becomes important

A heat pump drawing up to 3–7kW simultaneously with an EV charger drawing 7kW represents a significant combined load on a typical 80A or 100A domestic supply. Load balancing on the EV charger circuit prevents supply overload during simultaneous operation.

🏠

PME protection applies to both

On a PME supply, both the heat pump circuit and the EV charger circuit require appropriate PME protection. The EV charger’s WCED board addresses this for the EV circuit; the heat pump consumer unit handles its own circuit protection (Type B RCD, not PME-specific).

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Smart scheduling saves money

With an EV charger that supports smart tariff scheduling and a heat pump that can be programmed to run at off-peak times, the combined household energy cost can be significantly reduced. The two systems don’t need to talk to each other — scheduling each independently to off-peak windows is usually sufficient.

Frequently Asked Questions

Can I use a Type A RCBO in a heat pump consumer unit?
No. A Type A device cannot detect smooth DC leakage current, which is produced by the inverter-driven compressor in modern heat pumps. BS 7671 requires protection appropriate to the equipment’s leakage current characteristics. For heat pumps, this means a Type B RCD as a minimum.
Does the heat pump consumer unit replace the main consumer unit?
No. The heat pump consumer unit is a dedicated sub-board for the heat pump circuit. It is supplied from the main domestic consumer unit via a spare way (MCB), and provides the specific Type B RCD, SPD, and MCB protection required for the heat pump circuit downstream of the main board.
How do I know if my heat pump needs 20kHz Type B or standard Type B?
Check the heat pump manufacturer’s electrical installation manual. It will specify the required RCD type. Standard residential air source heat pumps (Vaillant aroTHERM, Daikin Altherma, Samsung EHS, Mitsubishi Ecodan etc.) typically require a standard Type B. VRF systems and some specialist commercial/high-efficiency models specify 20kHz. If in doubt, contact EcoHarmony and we’ll advise.
Does a heat pump need its own consumer unit or can I use a spare way in the main board?
The heat pump requires Type B RCD protection, which your main consumer unit (typically with Type A RCDs throughout) cannot provide on a standard spare way. A dedicated heat pump consumer unit fed from the main board is the practical and compliant solution. This keeps the Type B protection on the heat pump circuit without interfering with the rest of the installation.
Do I need PME/PEN fault detection for a heat pump?
PME/PEN fault detection is specifically required for EV charger installations under BS 7671 Regulation 722.411.4.1. There is no equivalent regulation requiring PME protection specifically for heat pumps. The heat pump consumer unit provides Type B RCD and SPD protection — PME protection is not a standard requirement for heat pump circuits.
What rating MCB do I need for a heat pump circuit?
Typically 20A for a standard residential air source heat pump, but this depends on the specific model’s maximum input current as stated in the installation manual. Always confirm with the manufacturer’s data sheet. The EcoHarmony heat pump consumer units include MCB protection sized for standard residential heat pumps — contact us if you need a specific rating for a non-standard application.
Can the heat pump and EV charger share a consumer unit?
Not practically, because they have conflicting protection requirements. The EV charger needs a Type A RCBO minimum (or PME board), the heat pump needs a Type B RCD. These are separate devices for separate circuits. Two dedicated sub-boards is the correct approach — a WCED board for the EV charger circuit, a heat pump consumer unit for the heat pump circuit, both fed from the main board.
🌡️

EcoHarmony — heat pump consumer units UK-stocked

Both Type B and 20kHz Type B heat pump consumer units in stock. Pre-assembled and tested — faster to install than sourcing and wiring individual components. Competitive pricing for heat pump installers and electrical contractors.

  • 🧠 Technical advice on Type B vs 20kHz selection for your heat pump model
  • 💷 Trade pricing — volume discounts for heat pump installation programmes
  • 📦 Fast dispatch — same-day on stock lines
  • 🔧 Also stock WCED boards for EV charger circuits on the same property

Installing a heat pump?

Standard Type B at £135 or 20kHz Type B at £235. Tell us the heat pump model and we’ll confirm which is correct.

Type B — £135 20kHz Type B — £235

Technical Glossary

Type B RCD
Residual current device that detects AC, pulsating DC, and smooth DC fault currents. Required for heat pump installations because inverter-driven compressors produce smooth DC leakage that Type A devices cannot detect.
20kHz Type B RCD
Type B RCD rated to detect leakage currents up to 20kHz. Required for heat pumps with high-frequency inverters (VRF systems, some high-efficiency residential models). Standard Type B detects up to approximately 1kHz.
Inverter drive
Electronic controller that converts AC mains power to variable-frequency AC to drive the compressor motor at different speeds. Enables variable capacity operation (COP optimisation). Present in all modern heat pumps. Produces DC leakage current as a by-product.
Smooth DC leakage
A type of fault current produced by inverter-driven equipment. Unlike pulsating DC (which Type A RCDs detect), smooth DC has no AC component. Type A and Type AC RCDs are blind to it. Type B RCDs detect it at their rated threshold (30mA).
VRF
Variable Refrigerant Flow — commercial and large-scale heat pump technology using variable compressor speed over a wide frequency range. Often requires 20kHz Type B RCD protection.
COP
Coefficient of Performance — the ratio of heat output to electrical energy input. A COP of 3 means 3kWh of heat for every 1kWh of electricity consumed. Inverter-driven heat pumps achieve higher average COP by modulating output to match demand rather than cycling on/off.
Type 2 SPD
Surge Protection Device installed at the distribution board. Required for heat pump installations due to the sensitivity of inverter electronics to transient overvoltages. Pre-included in both EcoHarmony heat pump consumer units.
Heat pump consumer units Type B & 20kHz Type B · EcoHarmony UK
Type B — £135 20kHz — £235

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