A Type B RCD is a residual current device designed to detect AC, pulsating DC and smooth DC leakage currents. That makes it suitable for circuits where standard Type AC and Type A devices may no longer provide the right protection.
Type B RCDs are commonly used on EV chargers, solar PV systems, battery storage, heat pumps and other inverter-driven equipment where smooth DC leakage may be present. In these applications, choosing the correct RCD type is critical for both safety and compliance.
Quick Answer: A Type B RCD detects AC, pulsating DC and smooth DC leakage currents. It is used where connected equipment can generate smooth DC fault currents that a Type A or Type AC device may not detect properly. Common examples include EV chargers, solar PV, battery storage, heat pumps and inverter-driven systems.
Browse all compliant options here: 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 – Installer Comparison
Choosing the wrong RCD type is one of the easiest ways to fail an inspection or build a callback into the job. This comparison shows exactly what each RCD type detects, where each one falls short, and why Type B is the only safe option on circuits that can generate smooth DC leakage.
| Feature | Type AC | Type A | Type B |
|---|---|---|---|
| AC leakage | ✔️ | ✔️ | ✔️ |
| Pulsating DC | ❌ | ✔️ | ✔️ |
| Smooth DC | ❌ | ❌ | ✔️ Required |
| EV / Solar compatible | ❌ | ⚠️ Limited | ✔️ |
Regulation Reminder: BS 7671 requires protection against DC fault currents. Where smooth DC leakage exceeds 6mA, a Type B RCD (or equivalent DC protection) is mandatory.
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 a Type B RCD Is Required
A Type B RCD is required wherever the connected equipment can generate smooth DC leakage currents that a Type A or Type AC device may not detect correctly.
That is why Type B protection is commonly specified for inverter-driven systems and circuits with DC-related fault characteristics.
Common cases where Type B may be required:
- EV chargers where suitable DC leakage protection is not provided elsewhere
- Solar PV inverters
- Battery storage systems
- Heat pumps with inverter compressors
- Variable speed drives (VFDs)
- Industrial motor control
If the equipment manufacturer specifies Type B protection, or smooth DC leakage is part of the circuit risk, Type B removes ambiguity and helps keep the install compliant.
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