Type B RCDs are the highest level of residual current protection used in UK electrical installations. They are designed for circuits where smooth DC leakage can occur - something Type AC and Type A devices cannot reliably detect.
With EV chargers, solar PV systems, battery storage, heat pumps and variable speed drives now common, Type B RCDs are no longer niche. In many installs, they are the only compliant option.
Quick Answer: A Type B RCD detects AC, pulsating DC and smooth DC leakage. It is required wherever inverter-driven equipment can produce continuous DC fault currents - including EV chargers, solar PV, battery systems, heat pumps and VFD-controlled motors.
Browse all compliant options here: Type B RCDs.
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What a Type B RCD Actually 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.
When a Type B RCD Is Required
You must use a Type B RCD wherever smooth DC leakage can be generated.
Common Type B applications:
- EV chargers (unless DC detection is built into the charger)
- Solar PV inverters
- Battery storage systems
- Heat pumps with inverter compressors
- Variable speed drives (VFDs)
- Industrial motor control
If the manufacturer specifies DC fault protection, Type B removes ambiguity and future-proofs the install.
Installer-Ready Type B RCDs & Boards
Below are installer-ready Type B options used on real EV, heat pump and renewable installs. These include 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 most common questions electricians ask when specifying Type B protection - especially on EV chargers, heat pumps and inverter-driven systems. If you’re unsure whether Type B is required, the answers below will clear it up quickly.
Are Type B RCDs mandatory for EV chargers?
Yes - unless the charger includes certified DC leakage detection. Without it, Type B is required.
Can I use Type A instead of Type B?
No. Type A does not detect smooth DC leakage and may fail to trip.
Do heat pumps require Type B protection?
Most inverter-driven heat pumps do. Always follow manufacturer guidance.
Why are Type B RCDs more expensive?
They use advanced sensing electronics capable of detecting complex fault currents.
👉 Need a compliant solution for EV, solar or heat pump installs? Browse all Type B RCDs