Heat pumps are becoming a common feature in UK homes and commercial sites, but their electrical demands are very different from a standard circuit. One of the most common questions from installers is simple: should you protect a heat pump with a Type A RCD, or does it need the more expensive Type B? Let’s break down the differences, the regulations, and what you should fit on site.
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What type of RCD is needed for a heat pump?
Under the 18th Edition Amendment 2, all new heat pump circuits require RCD protection. Because most heat pumps use inverter-driven compressors, they generate DC leakage currents that can blind or trip standard RCDs. That rules out Type AC entirely. At minimum, you’ll need a Type A, and in many cases a Type B is required depending on the manufacturer and system design.
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What’s the difference between Type A and Type B RCDs?
- Type A: Detects AC and pulsed DC up to 6 mA. Suitable for many single-phase appliances but may not handle smooth DC from inverters reliably.
- Type B: Detects all residual currents (AC, pulsed DC, and smooth DC up to higher levels). Designed for EV chargers, solar PV, and heat pumps with inverter drives. More expensive but provides full coverage.
In short: Type A covers most domestic scenarios, but Type B is the safest choice where manufacturer guidance is unclear or where inverter leakage is significant.
Can I use a Type A or Type B RCBO instead?
Yes. An RCBO combines overcurrent and earth leakage protection in one device. A Type B RCBO is often the simplest way to protect a dedicated heat pump circuit, especially in a subsidiary consumer unit.
Why not Type AC RCDs?
Type AC RCDs only detect pure AC leakage. They cannot reliably detect DC or mixed-frequency leakage from inverter technology. For this reason, they are effectively obsolete for new heat pump or EV installs and may cause failed EICRs if used on modern systems.
How to choose the correct RCD for a heat pump
The first rule is simple: follow the manufacturer’s installation manual. If a Vaillant, Daikin, or Mitsubishi heat pump specifies Type B, then that’s what you fit. If the documentation is unclear, industry guidance (HPA, NAPIT, NICEIC) recommends using Type B to guarantee compliance and avoid nuisance tripping. Where cost is a concern, Type A may be sufficient for smaller domestic units - but you’ll need to confirm against the spec sheet.
Recommended products for heat pump installs
- Heat Pump Type B RCD WHP240-030 – two-module, built for inverter-driven heat pumps
- Heat Pump Consumer Unit WME-HP40C – pre-assembled board with RCBO and SPD
- Surge Protection Devices – mandatory under Amendment 2 for new installs
Related Reading
- Do Heat Pump Installs Need Surge Protection?
- What Consumer Unit Do I Need for a Heat Pump?
- What Is a Time Delay RCD (S-Type) - And When Do You Need One?
Conclusion
For heat pump circuits, Type A is the minimum, but Type B gives you full coverage. With inverter-driven systems now standard, many installers are moving straight to Type B RCDs or RCBOs to guarantee compliance and reduce call-backs. Always confirm with the manufacturer, but when in doubt — fit Type B and sleep easy.