Helpful video reference. We use eFIXX's "How Do I Pick the Right RCD for a Heat Pump?" as the video reference here. eFIXX is a UK electrical trade publisher and the video covers the Type A versus Type B versus Type F question clearly, including real-world nuisance trip scenarios and the HPA guidance that followed the BEAMA RCD Handbook.
1. Why standard Type A RCDs cause problems with heat pumps
Every domestic RCD you encounter in a standard UK installation is a Type A device. Type A detects AC fault currents and pulsating DC -- the kind produced by single-phase rectifiers. That covers most domestic appliances well enough.
The problem with heat pumps is the inverter drive. Modern variable-speed compressors use a three-phase inverter to regulate output, and those power electronics produce smooth DC leakage current as well. Type A RCDs do not detect smooth DC. In practice, DC leakage from a heat pump can saturate the magnetic core of a Type A RCD, reducing its sensitivity -- and in some cases causing it to trip on legitimate transient currents during start-up rather than genuine faults.
2. What makes inverter-driven compressors different
A traditional single-speed compressor runs at one speed and produces a relatively simple electrical signature. Inverter-driven compressors vary their speed continuously using pulse-width modulated switching, which produces high-frequency leakage currents across a wide spectrum. These currents do not fit neatly into the AC waveform that a Type A RCD is designed around.
The degree of leakage depends on the specific heat pump model, its cable length, and how the power electronics are designed. This is why there is no single universal answer -- and why manufacturer guidance matters.
3. Type F: the midpoint choice
A Type F RCD was specifically developed for inverter-driven loads including variable-speed motors, washing machines and air conditioning units. It detects AC currents, pulsating DC currents, and mixed-frequency AC currents up to 1 kHz. For many heat pump models -- particularly those from manufacturers who have assessed their products against Type F -- this is sufficient.
Type F devices are more widely available than Type B and cost considerably less. A Type F RCBO for a single circuit can be found in most DIN rail enclosures from major UK manufacturers, which makes integrating the heat pump circuit into an existing consumer unit far easier.
4. Type B: the widest protection
A Type B RCD covers everything a Type F covers, plus it detects smooth DC fault currents and frequencies above 1 kHz. This is the device that offers the broadest protection for inverter-driven loads and is required by the IET Wiring Regulations (BS 7671) for Mode 3 EV charger installations on PME supplies.
The catch is cost and form factor. Type B RCDs are significantly more expensive, and -- unlike Type A and Type F -- there is no single-module RCBO format with Type B earth leakage protection available in the standard DIN rail sizes used in UK domestic consumer units. In practice, a Type B installation usually means a separate two-pole or four-pole RCD enclosure ahead of the circuit MCB, which adds cost and complexity.
5. What the Heat Pump Association and BEAMA say
Following a period of industry confusion (some installers fitting Type A, others insisting on Type B), the Heat Pump Association produced guidance in 2024 in conjunction with NAPIT and the NICEIC. The position is:
- Check the heat pump manufacturer's installation data sheet first. Many manufacturers now specify Type F or Type A+ (an enhanced Type A) as sufficient for their products.
- If the data sheet gives no guidance, or the guidance is unclear, use Type B as the safe default.
- Type A alone is generally not sufficient for inverter-driven heat pumps and should not be used unless the manufacturer explicitly states it is adequate.
BEAMA's RCD Handbook, produced with ABB, Schneider, Hager and Legrand, covers the same ground and provides the theoretical basis for the HPA position.
6. What to do in practice
Before any heat pump supply circuit is designed, request the installation manual for the specific model. Look for a section on protective devices, RCD requirements, or electrical protection. Most European manufacturers now include an explicit statement on RCD type following years of industry confusion.
If the manual says Type F or Type A+: fit that device and document the basis for the choice on the electrical installation certificate.
If the manual is silent or ambiguous: fit Type B. The extra cost is worth the certainty, and you have a clear basis for the decision if the installation is ever inspected.
7. Existing heat pump installations
If a heat pump was installed with a Type A RCD and is causing repeated nuisance trips -- particularly at start-up -- this is a likely explanation. The fix is to replace the protective device with a Type F or Type B unit. That work falls within Part P and needs a qualified electrician, but it is straightforward and resolves the problem in almost every case.
When to call us
New heat pump supply circuits are Part P notifiable work. If you are commissioning a new heat pump, having repeated nuisance trips from an existing circuit, or want an EICR to check over the installation, call. Small jobs in Sandwich are charged at £10 per 10 minutes.
Heat pump supply or RCD change in east Kent?
Richard handles dedicated supply circuits, RCD upgrades and EICR inspections for heat pump installations in Sandwich and the surrounding area.
Contact Richard