Heat Pump Electrical Protection Requirements UK | RCD

Heat Pumps

Heat Pump Electrical Protection Requirements

Heat pumps are not ordinary electrical loads. Their inverter-driven compressors can produce fault currents that a standard RCD does not detect, so the protection has to be chosen to suit the equipment.

Quick answer

Most inverter-driven heat pumps need Type B RCD protection rather than Type A, plus a Type 2 SPD and correctly rated overcurrent protection. The heat pump manufacturer’s installation manual states the RCD type, and BS 7671 (Reg 531.3.3) requires the device to suit the equipment. See What is a Type B RCD? for how the types differ.

Why heat pumps need Type B protection

A heat pump’s inverter converts the incoming AC supply into variable-frequency AC to run the compressor at different speeds. That conversion can produce smooth DC leakage current under fault conditions. A Type A RCD detects AC and pulsating DC, but not smooth DC, so a genuine fault of that kind can pass without tripping the device.

RCD type	AC faults	Pulsating DC	Smooth DC	Typical heat pump use
Type AC	Yes	No	No	Not suitable
Type A	Yes	Yes	No	Only where the manufacturer specifies it
Type B	Yes	Yes	Yes	Most inverter-driven heat pumps
Type B, high-frequency rated	Yes	Yes	Yes, at higher frequencies	Where the manufacturer specifies a high-frequency RCD (for example 20kHz)

Check the manual, not the heat pump’s price or brand

The required RCD type is stated in the heat pump’s installation manual. Wording such as “Type B required” or “frequency-sensitive RCD” tells you which device to fit. If it is unclear, ask the manufacturer before you specify.

Standard Type B or high-frequency Type B?

Most residential air and ground source heat pumps are covered by a standard Type B device. Some systems, such as variable refrigerant flow (VRF) units, commercial heat pumps and certain high-efficiency residential models, have inverters that switch at higher frequencies, and the manufacturer specifies a high-frequency-rated Type B RCD.

EcoHarmony stocks both options as pre-assembled units, see heat pump protection units explained.

Surge protection

Inverter electronics and control boards are far more vulnerable to transient overvoltages than simple resistive loads. BS 7671 requires the need for surge protection to be assessed, and for a heat pump the answer is almost always to fit a Type 2 SPD at the board feeding it. See surge protection for solar and heat pumps.

Separate board or spare way?

A main consumer unit with Type A RCD protection throughout cannot provide Type B protection on an ordinary spare way. The usual solution is a dedicated heat pump sub-board, fed from a way on the main board, holding the Type B RCD, SPD and overcurrent protection for that circuit.

Overcurrent protection is sized to the heat pump’s maximum input current in the manufacturer’s data, not a standard figure, so always confirm it for the specific model.

Heat pump and EV charger on the same property

Put each on its own circuit with its own protection, as the RCD requirements differ
On a PME supply the EV circuit needs PEN fault protection under BS 7671 Reg 722.411.4.1; that regulation applies to EV charging, not heat pumps
A heat pump and EV charger running together are a large combined load, so check supply capacity and consider load management on the EV circuit

See What is PME in EV charging? for the EV side.

Frequently asked questions

Can I use a Type A RCBO for a heat pump?

Only where the heat pump manufacturer specifies Type A. For inverter-driven heat pumps the manufacturer more often specifies Type B, and fitting Type A where Type B is required leaves a gap in protection against smooth DC faults.

Does a heat pump replace my main consumer unit?

No. The heat pump sub-board is fed from a way on the main board and protects only the heat pump circuit.

How do I know if I need a high-frequency Type B?

The manufacturer’s installation manual states it. If it says Type B without a frequency qualification, a standard Type B is normally appropriate. If it names a high frequency such as 20kHz, use a high-frequency-rated device.

Do heat pumps need PEN fault protection?

Reg 722.411.4.1 addresses EV charging installations. It does not set an equivalent requirement for heat pumps, so the heat pump circuit is protected with the RCD type, SPD and overcurrent device the manufacturer and BS 7671 call for.

What size MCB does a heat pump need?

It depends on the model’s maximum input current, so use the figure in the manufacturer’s data rather than a standard value.

Heat PumpsHeat Pump Protection Units Explained Heat PumpsHeat Pump Tripping: Electrical or Heating Fault?RCDs & RCBOsWhat Is a Type B RCD?Surge ProtectionSurge Protection for Solar and Heat Pumps

Not sure what your install needs?

Use the Product Finder →