Three-phase circuits need earth leakage protection just as much as single-phase ones - but the device that does the job is different. A 3-phase RCD (also called a 4-pole RCD) is designed to protect three-phase loads, machinery and distribution boards by disconnecting all live conductors when leakage is detected.
Quick Answer: A 3-phase RCD is a 4-pole earth leakage protection device used on three-phase circuits. It trips when imbalance is detected between phases and neutral, protecting equipment and preventing electric shock. They’re essential on three-phase machinery, commercial boards, EV chargers, heat pumps and plant equipment.
Browse the full range here: 3-Phase RCDs.
This guide explains how they work, where you need them, and the difference between high-immunity, Type A and Type B 4-pole RCDs.
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What a 3-Phase RCD Actually Does
A 3-phase RCD monitors all live conductors (L1, L2, L3 and N) for leakage. If current flowing out doesn’t match the current coming back, the RCD disconnects the entire circuit within milliseconds.
This gives protection against:
- Indirect contact - preventing shock if exposed metal becomes live
- Insulation faults on machinery and three-phase motors
- Leakage in inverter-driven equipment like heat pumps and EV chargers
- Fire risk reduction from persistent leakage
Because three-phase loads handle higher power and more complex waveforms, the RCD must disconnect all live conductors simultaneously. That’s why these devices are 4-pole, not just 2-pole.
Where 3-Phase RCDs Are Required
Anywhere a three-phase circuit supplies equipment that needs earth leakage protection, a 4-pole RCD is required. This is common across commercial and industrial sites, but increasingly domestic too due to EV and heat pump installs.
Common applications:
- Three-phase distribution boards
- Workshop machinery (lathes, saws, compressors, CNC)
- EV chargers and rapid charging points
- Heat pumps and inverter-driven systems
- Solar inverters & battery systems
- Plant rooms and industrial panels
Many devices also require a specific RCD type depending on harmonic content and leakage behaviour. That’s where Type A, Type B and high-immunity variants come in.
Type A, Type B & High-Immunity Options
Three-phase loads vary massively, so picking the right RCD type matters. Here’s the quick breakdown.
Type A 4-Pole RCDs
Handles AC and pulsating DC leakage. Suitable for most modern equipment including EV chargers, heat pumps and inverter-driven units.
- Most common domestic/commercial choice
- Works with single-phase and three-phase loads
- Required for many EV and renewable installs
High-Immunity (HI) RCDs
Designed to resist nuisance tripping in environments with high harmonics or inrush currents.
- Excellent for inverter-driven equipment
- Ideal for heat pumps, solar and EV chargers
- Reduces false trips on machinery start-up
Type B 4-Pole RCDs
Handles smooth DC leakage and high-frequency signals. Required for EV fast chargers, PV inverters, VFDs and machinery with complex electronics.
- The safest option for heavy inverter loads
- Protects against DC saturation
- Common in commercial EV and renewable systems
Installer-Favourite 4-Pole RCDs
Here are dependable Type A, Type B and high-immunity options for three-phase boards.
- 63A 4-Pole Type A RCD – High Immunity
- 40A 4-Pole Type A RCD – High Immunity
- 80A 4-Pole Type A RCD – High Immunity
- 100A 4-Pole Type A RCD – High Immunity
- 80A 4-Pole A-Type RCD – 100mA Time-Delay
- 63A 4-Pole A-Type RCD – 100mA Time-Delay
- 100A 4-Pole A-Type RCD – 100mA Time-Delay
- 63A 4-Pole Type B RCD
Browse all models here: 3-Phase RCDs.
FAQs
Installers regularly ask these when specifying three-phase RCD protection.
Do all three-phase circuits need an RCD?
Not always, but most modern equipment (EV chargers, heat pumps, inverters, plant) requires leakage protection. Check manufacturer guidance and BS 7671.
Is a 4-pole RCD the same as a 3-phase RCBO?
No. An RCBO adds overcurrent protection. A 4-pole RCD is leakage-only. Many installations pair RCDs with three-phase MCBs.
When should I use a Type B 3-phase RCD?
When the load includes smooth DC leakage - e.g. EV rapid chargers, large solar inverters, VFD-driven machinery.
Are high-immunity RCDs worth it?
Yes, especially on inverter-driven loads. They significantly reduce nuisance tripping from harmonics or motor start-up surges.
👉 Need reliable three-phase leakage protection? Browse all 3-phase RCDs