What Is a Type B 4-Pole RCCB?
A 4-pole RCCB connects three-phase conductors (L1, L2, L3) and the neutral (N), matching the topology of three-phase-four-wire Distribution Boards. The "Type B" designation means the device can detect:
- Sinusoidal AC residual current (50/60 Hz)
- Pulsating DC residual current
- Smooth DC residual current
- Defined higher-frequency AC residual current up to 1 kHz per IEC 62423
This contrasts with Type AC (AC-only) and Type A (AC + pulsating DC) devices, which cannot reliably detect smooth DC and may suffer from "DC blinding"—in which a DC component pre-magnetizes the sensing core, degrading the device's ability to detect a subsequent AC fault.
A 4-pole device is intended for three-phase circuits with neutral. For three-wire three-phase loads without neutral, the selection must follow the equipment manufacturer's instructions and the approved device wiring diagram.
Why Type B? The Smooth-DC Problem in Modern Loads
Modern power-electronic loads change the residual-current waveform in ways that Type AC and Type A devices were not designed to handle:
| Load Type | Leakage Characteristics | Type B Relevance |
|---|---|---|
| EV chargers | Rectifiers generate pulsating + smooth DC | Required where DC leakage can exceed Type A limits |
| PV inverters (transformerless) | Smooth DC injection from DC side to AC side | Standard recommendation for inverter AC output |
| Variable-frequency drives (VFDs) | Harmonics + DC components from rectifier stage | Needed for reliable protection |
| Battery energy storage (BESS) | Bidirectional smooth DC leakage | Required for comprehensive protection |
| UPS / medical imaging | Mixed AC + DC residual currents | Type B provides full-spectrum detection |
The 6 mA figure is frequently referenced in EV and electronic-load discussions as a common limit associated with the smooth-DC tolerance of Type A protection. It is not a universal rule that replaces equipment instructions or local regulations. If a circuit can exceed the permitted DC component, the design needs a Type B RCCB or a compliant DC-detection solution.
Key Specifications (Typical 4-Pole Type B RCCB)
Based on IEC/EN 61008-1 and IEC/EN 62423 compliant products:
| Parameter | Typical Range |
|---|---|
| Standards | IEC/EN 61008-1, IEC/EN 62423 |
| Poles | 4P (3P+N) |
| Rated voltage (Un) | 400/415 V AC |
| Rated current (In) | 16 A, 25 A, 32 A, 40 A, 63 A, 80 A, 100 A |
| Rated residual operating current (Idn) | 30 mA / 100 mA / 300 mA / 500 mA |
| Rated short-circuit breaking capacity (Idm) | 10 kA |
| Frequency | 50/60 Hz |
| Tripping time | <= 0.1 s at Idn |
| Mounting | 35 mm DIN rail |
| Connection capacity | 1.5–25 mm2 |
| IP rating | IP20 (front face) |
| Operating temperature | -25 C to +55 C |
| Endurance | 2000 electrical / 4000 mechanical cycles |
Note: Exact values vary by model. Always verify against the product datasheet.
Quick Selection Guide: Which Type B 4P RCCB Do You Need?
| Application | Recommended Poles | Recommended Idn | Typical In | Notes |
|---|---|---|---|---|
| Single EV charger (7.4 kW) | 2P | 30 mA | 32 A | Use Type B if charger manual requires it |
| Three-phase EV charger (22 kW) | 4P | 30 mA | 40 A | Mandatory Type B in many codes |
| Three-phase PV inverter (10-30 kW) | 4P | 100 mA | 63 A | Fire protection; check local code |
| VFD group (multiple drives) | 4P | 300 mA | 100 A | Selectivity with upstream protection |
| UPS / medical imaging | 4P | 30 mA | 63 A | Additional shock protection required |
Not sure? Contact our engineering team for a free load-based recommendation.
How to Select a Type B 4-Pole RCCB: 5 Decision Points
- Confirm the neutral is present and switched. A 4-pole device is for three-phase-four-wire circuits. Verify that all conductors belonging to the protected circuit pass through the RCCB exactly as the manufacturer's diagram specifies.
- Match In to the design load. Select rated current based on the actual continuous load, conductor capacity, and ambient conditions—not merely the nameplate value.
- Choose Idn by protection objective.
- 30 mA: additional shock protection for circuits that can be touched (most electrical codes require this for accessible circuits)
- 100 mA: fire protection or equipment protection where 30 mA would cause nuisance trips
- 300 mA: fire protection in industrial main distribution
- 500 mA: specific industrial applications
- Verify short-circuit coordination. Ensure the 10 kA (typical) breaking capacity is compatible with the upstream backup fuse or breaker.
- Check tripping characteristic. Select instantaneous, short-time-delay, or selective (Type S) tripping depending on whether the device is at the main incomer or in a selectively-coordinated cascade.
Application Scenarios That Call for Type B 4P
Three-Phase EV Charging Stations
Three-phase EV chargers (11 kW, 22 kW) contain rectifiers that generate both pulsating and smooth DC. A Type B 4P RCCB at the AC supply side provides comprehensive protection. See our EV charging protection solution page.
Three-Phase PV and Storage Systems
Transformerless PV inverters can inject smooth DC residual current onto the AC side. For three-phase PV systems connected to the grid, a 4P Type B RCCB is typically required at the inverter output.
Variable-Frequency Drives
VFDs in industrial automation generate harmonics and DC components through their rectifier stage. When multiple drives share a feeder, a Type B 4P RCCB provides the detection that Type A cannot.
Medical imaging devices and UPS systems with DC components demand full-spectrum residual current detection.
Type B vs. Type B+: When Frequency Response Matters
Standard Type B devices per IEC 62423 detect AC residual currents up to 1 kHz. For installations employing silicon-carbide (SiC) or gallium-nitride (GaN) converters switching at higher frequencies, Type B+ variants extend detection to 20 kHz, maintaining sensitivity where standard Type B devices exhibit reduced response.
Type B performance should not be described as "all frequencies." Always check the datasheet for the specific frequency range claimed.
Installation and Commissioning Checklist
- Verify wiring polarity — follow the manufacturer's diagram for L1/L2/L3/N terminal positions (N-left vs N-right varies by model)
- Confirm supply direction — some electronic-type B devices depend on correct supply polarity for smooth-DC detection
- Perform the test-button function — verify mechanical trip operation
- Measure insulation resistance of the downstream circuit prior to closing
- Document Idn and In settings against the load schedule
- Schedule periodic testing — functional test interval per local code or manufacturer recommendation
Frequently Asked Questions
Is a Type B 4P RCCB mandatory for every three-phase circuit?
No. Type B is specified when the load can create smooth DC or high-frequency residual currents. The decision should follow the load manufacturer's instructions, the fault-current risk assessment, and local installation codes. For simple three-phase AC loads with no power electronics, Type A may be permissible under local rules.
Can I replace a Type A 4P with a Type B 4P directly?
Physically, yes—if the poles, voltage, current rating, and DIN-rail footprint match. But the upgrade should be justified by the actual load profile. Simply installing Type B without verifying the load's DC-leakage characteristics does not guarantee compliance.
What is the difference between a Type B RCCB and a Type B RCBO?
An RCCB provides residual-current protection only. An RCBO (Residual Current Circuit Breaker with Overcurrent protection) combines residual-current and overcurrent (short-circuit and overload) protection in a single device. In space-constrained sub-panels, a Type B RCBO may be preferable; in main distribution boards, a Type B RCCB paired with upstream MCBs is often more economical.
Does Type B detect all frequencies?
Per IEC 62423, Type B detects sinusoidal AC residual currents up to 1 kHz, plus pulsating and smooth DC. For frequencies above 1 kHz, Type B+ variants extend the range—but this is a model-specific claim; always consult the datasheet.
How do I verify a Type B RCCB is compliant?
Look for certification marks (CE, CB, TUV, UKCA) referencing IEC/EN 61008-1 and IEC/EN 62423. Request the manufacturer's test report confirming smooth-DC detection performance per IEC 62423.
Key Takeaways
- A Type B 4-pole RCCB is the correct specification for three-phase-four-wire circuits where loads may generate smooth DC, pulsating DC, or high-frequency residual currents.
- Selection must follow load data + equipment manufacturer instructions + local wiring rules—not a one-size-fits-all rule.
- Compliant devices meet IEC/EN 61008-1 and IEC/EN 62423, with 4P ratings typically at 400/415 V AC, 16-100 A, 30-500 mA sensitivity, and 10 kA breaking capacity.
- For SiC/GaN high-frequency converters, consider Type B+ extending detection to 20 kHz.
- Correct wiring (neutral position, supply direction) and periodic functional testing are essential to maintain protection integrity.
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