Heat pumps are now one of the most common inverter-driven loads installed in UK homes. While they look like a traditional heating appliance, electrically they behave very differently - and that has important implications for RCD protection.
The key question installers ask is simple: does a heat pump require Type B RCD protection? The answer depends on DC leakage risk, inverter design, and manufacturer guidance.
Quick Answer: Many heat pumps do require Type B RCD protection because their inverter-driven compressors can generate smooth DC leakage. Where DC fault current may exceed 6mA, Type B (or equivalent DC protection) is required under BS 7671.
For compliant, installer-ready solutions, see: Heat Pump Consumer Units.
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Why Heat Pumps Can Produce DC Leakage
Modern heat pumps use inverter-driven compressors to modulate output and improve efficiency. This requires internal rectifiers and variable frequency drives.
These components can introduce:
- Pulsating DC leakage
- Smooth (continuous) DC leakage
- High-frequency fault currents
This behaviour is electrically similar to EV chargers and solar inverters - and it creates the same risk of DC blinding in Type AC and Type A RCDs.
BS 7671 Rules on DC Leakage
BS 7671 requires RCDs to operate correctly under all expected fault conditions.
Where equipment can produce smooth DC fault current exceeding 6mA, standard RCDs may not trip.
Compliance Note: If smooth DC leakage above 6mA is possible, BS 7671 requires Type B RCD protection or an alternative method that provides equivalent DC fault detection.
This requirement applies regardless of whether the load is classed as “heating” - the electrical behaviour is what matters.
When Does a Heat Pump Need Type B RCD Protection?
A Type B RCD is required where the heat pump:
- Uses an inverter-driven compressor
- Does not include certified DC leakage detection
- Is supplied via a dedicated circuit
- Has manufacturer guidance referencing DC fault current
In practice, many modern air source and ground source heat pumps fall into this category.
Where manufacturer documentation is unclear, specifying Type B is the safest way to ensure compliance and future-proof the installation.
Compliant Consumer Units for Heat Pump Circuits
Using a dedicated consumer unit simplifies heat pump installations and ensures correct segregation, protection and labelling.
Purpose-built heat pump boards typically include:
- Type B RCD or Type A with verified DC protection
- Correct MCB sizing for compressor startup currents
- Space for surge protection devices (SPDs)
- Clear labelling for inspection and certification
Explore installer-ready options here: Heat Pump Consumer Units.
FAQs
These FAQs cover the most common questions around heat pumps, inverter DC leakage, and when Type B RCD protection is required.
Do all heat pumps require Type B RCDs?
No - but many do. It depends on inverter design and DC leakage risk.
Can Type A RCDs be used on heat pumps?
Only if the manufacturer confirms DC leakage will not exceed 6mA.
What happens if DC leakage blinds the RCD?
The RCD may fail to trip during a fault, creating a shock or fire risk.
Is a dedicated consumer unit recommended?
Yes. It simplifies compliance, inspection and future maintenance.
👉 Specifying a heat pump circuit? View compliant heat pump consumer units