Heat Pump Protection Units Explained

Heat pump installations require a dedicated circuit with appropriate RCD protection — typically a B-type RCD rated for the heat pump's start-up current. Purpose-built WCED heat pump enclosures provide compliant protection in a ready-to-install format, eliminating the need to source and assemble components individually.

Heat pump installations have grown rapidly across the UK since the introduction of the Boiler Upgrade Scheme and changes to building regulations restricting gas boiler installation in new builds. With this growth has come increased scrutiny of the electrical installation requirements — particularly around RCD protection type, enclosure specification, and supply circuit design. Getting the electrical protection wrong can result in nuisance tripping, equipment damage, or a non-compliant installation.

What type of RCD does a heat pump need?

Most domestic air source heat pumps require a Type A or Type A-HP (heat pump optimised) RCD rather than a standard Type AC device. The heat pump's inverter drive — which controls the compressor speed — can produce pulsating DC leakage currents that a Type AC device would not reliably detect. Some manufacturers specifically require a Type B RCD, particularly for larger units or those with 3-phase supplies.

The WCED WHP series provides dedicated heat pump RCDs — specifically the WHP240B-030, a 2-pole 40A 30mA Type B device designed and tested for compatibility with heat pump inverter drives including Vaillant arotherm+ and similar systems. Where the manufacturer specifies Type A, the standard WCED WER Type A RCBOs are appropriate.

Always check the manufacturer's documentation

Heat pump RCD requirements vary by manufacturer and model. Always check the installation manual before specifying protection. Common requirements include:

Manufacturer / model type	Typically specified RCD
Vaillant arotherm+ (single phase)	Type B 30mA (WHP240B-030)
Samsung EHS (single phase)	Type A or Type A-HP 30mA
Mitsubishi Ecodan (single phase)	Type A 30mA
Daikin Altherma (single phase)	Type A 30mA
Most 3-phase heat pumps	Type B 4-pole 30mA

WCED heat pump enclosures

The WCED WME5/HP4016S and WME08/HP40C are fully assembled heat pump protection units — metal IP40 enclosures pre-wired with a main isolator, Type B HP RCD, SPD, and circuit MCBs appropriate for a domestic heat pump installation. These units are designed to be mounted adjacent to the heat pump outdoor unit or at the consumer unit position, and connect directly to the incoming supply and the heat pump circuit.

Type B HP RCD (WHP series) — heat pump optimised

Main isolator — 40A or 63A to suit heat pump rating

SPD — Type 2 40kA surge protection included

Metal IP40 construction — indoor mounting

Pre-wired — ready to connect on site

Vaillant compatible tested

Shop WCED Heat Pump Protection Units

Fully assembled heat pump enclosures with Type B RCD, isolator, and SPD. Metal IP40. In stock.

View heat pump units →

Frequently Asked Questions

Can I use an existing circuit for a heat pump or does it need a dedicated supply?

Heat pumps require a dedicated supply circuit — they should not share a circuit with other loads. The supply must be sized for the heat pump's maximum current draw (plus any diversity factor for supplementary heating elements), and the protective device must be rated accordingly. A dedicated consumer unit way with the appropriate RCD and MCB (or RCBO) is the correct approach.

What cable size is needed for a heat pump circuit?

Cable sizing depends on the heat pump's rated current, cable length, and installation method. As a guide, a 6kW single-phase heat pump drawing approximately 25A typically requires 4mm² or 6mm² twin and earth depending on run length and clipping method. Always size cables in accordance with BS 7671 Table 4D and the manufacturer's minimum cable specifications.

Does a heat pump installation need to be notified to Building Control?

The electrical installation for a heat pump is notifiable work under Part P of the Building Regulations in England and Wales. It must be carried out by a registered competent person (NAPIT, NICEIC, etc.) or inspected and certified by Building Control. The heat pump itself may also require MCS certification for BUS grant eligibility.

Further reading:
What is a Type B RCD?
Surge protection for solar and heat pumps
Fully assembled consumer units explained
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