What Is a Type B RCD? What It Detects and When It Is Used
A Type B RCD detects sinusoidal AC, pulsating DC and smooth DC residual currents, including residual currents associated with many inverter and frequency-converter loads.
That wider detection range makes Type B relevant to some EV charging, solar PV, battery storage, heat pump, UPS and variable-speed drive circuits. The connected equipment, manufacturer instructions and overall protective arrangement determine whether it is required.
Quick Answer: Type B covers the AC and pulsating DC residual currents detected by Type A, plus smooth DC residual current. It is selected where equipment can produce residual-current characteristics that Type A is not designed to detect.
Browse our Type B RCD range. For a direct comparison, read Type A vs Type B RCDs.
Jump to:
What a Type B RCD Detects
Type B RCDs are designed for modern power electronics. They detect fault currents that simpler devices physically cannot see.
- Standard AC leakage
- Pulsating DC leakage
- Smooth (continuous) DC leakage
- High-frequency leakage from inverter switching
Why this matters
Smooth DC leakage can blind Type AC and Type A RCDs, preventing them from tripping during a fault. This creates a serious shock and fire risk - particularly on EV and renewable circuits.
Type B vs Type A vs Type AC RCDs
The correct RCD type depends on the residual-current characteristics of the connected equipment. Type B is not automatically required simply because a circuit contains electronics.
| RCD type | Residual current detected | Typical selection context |
|---|---|---|
| Type AC | Sinusoidal AC | Fixed equipment known to contain no DC components |
| Type A | AC and pulsating DC | Many modern electronic loads |
| Type B | AC, pulsating DC and smooth DC, including specified frequency components | Equipment capable of producing smooth DC or complex residual currents |
Where Type B RCDs Are Used
Type B RCDs are used on circuits where connected equipment may produce smooth DC leakage currents. In practice, that usually means modern electrical systems built around power electronics, inverters or variable-speed control.
Common applications include:
- EV charger circuits
- Solar PV inverters
- Battery storage systems
- Heat pumps with inverter compressors
- Variable speed drives and motor control
- Some three-phase inverter-driven installations
This is why Type B protection often appears on renewable, EV and commercial power systems rather than standard domestic socket or lighting circuits.
When Is a Type B RCD Required?
Type B protection is used where the equipment or installation can produce smooth DC or other residual-current characteristics outside Type A capability.
- The equipment manufacturer specifies Type B.
- The converter or inverter can produce smooth DC residual current and no suitable equivalent protection is provided elsewhere.
- The system design requires Type B detection across the relevant conductors and frequencies.
This can apply to some EV chargers, PV inverters, battery systems, heat pumps, UPS equipment and VFDs, but the product documentation remains decisive. Built-in 6 mA DC detection, such as an RDC-DD in an EV charger, may change the upstream RCD requirement.
Installer-Ready Type B RCDs & Boards
If you need a Type B RCD for an EV charger, solar PV system, heat pump or inverter-driven circuit, these are the kinds of products installers typically specify. The range includes standalone Type B RCDs for dedicated circuits, plus pre-configured consumer units designed to simplify compliance and reduce on-site wiring time.
Standalone Type B RCDs
Type B Consumer Units for Heat Pumps & Renewables
- 6-Way Metal Unit with 100A Type B RCD
- 8-Way Heat Pump Consumer Unit
- 10-Way Heat Pump Consumer Unit
- 12-Way Heat Pump Consumer Unit
View the full range: All Type B RCDs
FAQs
These are the common questions electricians ask when deciding whether a Type B RCD is needed on an EV charger, solar PV system or other inverter-driven circuit.
What is a Type B RCD?
A Type B RCD is a residual current device that detects AC, pulsating DC and smooth DC leakage currents. It is used where standard Type A or Type AC devices may not provide suitable protection.
What is the difference between Type A and Type B RCDs?
Type A detects AC and pulsating DC leakage. Type B also detects smooth DC leakage, which makes it suitable for more complex inverter-driven applications.
Are Type B RCDs mandatory for EV chargers?
They may be required where suitable DC leakage protection is not already provided by the charger or the wider protective arrangement.
Do solar PV systems need a Type B RCD?
Some do. It depends on the inverter characteristics and manufacturer requirements. Where smooth DC leakage is part of the risk, Type B may be required.
Can I use Type A instead of Type B?
Only where the protective requirements of the equipment and installation allow it. If smooth DC leakage is possible, Type A may not be sufficient.
👉 Need a compliant solution for EV, solar or heat pump installs? Browse all Type B RCDs