What is the difference between Type AC, Type A and Type F/B residual current circuit breakers (30 mA vs 300 mA)?
Compare Type AC, Type A, Type F and Type B residual current circuit breakers (RCCB) by detected fault waveform (sinusoidal AC, pulsating DC, smooth DC) and 30 mA vs 300 mA thresholds.
What is the main difference between Type AC, Type A and Type F/B residual current circuit breakers? In residual current circuit breakers (RCCBs), the letter type defines which earth-fault current waveforms the magnetic core can detect, while the milliampere (mA) rating defines the protection purpose: Type AC detects only pure 50/60 Hz sinusoidal alternating residual currents; Type A detects sinusoidal AC plus pulsating direct current (DC) faults produced by single-phase rectifiers; Type F and Type B detect high-frequency composite waveforms and smooth DC residual currents produced by variable frequency drives (VFDs), UPS systems and EV chargers. 30 mA protects human life against electric shock, whereas 300 mA protects buildings against electrical fire.
Type AC, A, F and B RCCB comparison table
| Criterion | Type AC RCCB | Type A RCCB | Type F RCCB | Type B RCCB |
|---|---|---|---|---|
| Detected Waveform | Pure 50/60 Hz sinusoidal AC only | Sinusoidal AC + pulsating DC (up to 6 mA smooth DC) | Type A + composite frequencies up to 1 kHz (up to 10 mA smooth DC) | Type F + smooth DC residual currents and high-frequency faults |
| Blinding Risk on Electronic Loads | Magnetic core can saturate and fail to trip under pulsating DC | Can saturate if smooth DC fault current exceeds 6 mA | Safe for single-phase inverters; limited on 3-phase bridge rectifiers | Full protection even under smooth DC earth faults |
| Typical Application | Resistive heaters, incandescent lighting, basic socket circuits | Inverter HVAC, washing machines, LED drivers, IT/UPS socket circuits | Single-phase variable-speed pumps, heat pumps, HVAC fans | 3-phase VFDs, EV charging stations, solar PV inverters, medical panels |
| 30 mA Option (Personnel Protection) | Basic socket-outlet and wet-room final circuits | Residential, commercial and industrial final circuits | Variable-speed single-phase machine feeders | EV chargers, laboratories and VFD-fed final circuits |
| 300 mA Option (Fire Protection) | Main distribution and sub-main riser fire protection | Main distribution fire protection in buildings with electronic loads | Industrial sub-panel incomers | VFD and solar PV main combiner panels |
| Popular Rated Currents | 25 A · 40 A · 63 A | 25 A · 40 A · 63 A · 80 A | 40 A · 63 A | 40 A · 63 A · 100 A |
| Pole Configurations | 2P (Single-Phase) · 4P (Three-Phase) | 2P · 4P | 2P · 4P | 4P |
| Category and Guide | Residual Current Circuit Breakers | Residual Current Circuit Breakers · Selection Guide | Residual Current Circuit Breakers | Residual Current Circuit Breakers · Toroidal Current Transformers |
How should 30 mA personnel protection and 300 mA fire protection be coordinated?
To guarantee both shock protection and supply continuity, 30 mA and 300 mA residual current circuit breakers must be coordinated across distribution levels:
- 30 mA on final socket-outlet and wet-area circuits: Currents above 30 mA through the human body create a risk of ventricular fibrillation. Final socket circuits, bathrooms/kitchens and field socket boxes require a 30 mA RCCB or dedicated per-circuit RCBOs.
- 300 mA (Time-Delayed / Type S) on main incomers and risers: Insulation tracking faults of ~300 mA (~65–70 W of localized heat) can ignite fires. To prevent a downstream 30 mA fault from tripping the entire building incomer, upstream 300 mA devices should be selective (Type S / time-delayed) or implemented with a toroidal current transformer.
- Avoid placing a Type B load downstream of an upstream Type AC/A RCCB: Smooth DC fault current from a three-phase VFD or EV charger can saturate an upstream Type AC or Type A toroidal core, blinding it to simultaneous AC faults.
Frequently asked questions
What does the 40 A (In) rating on an RCCB mean—does it trip on overload?
The 25 A, 40 A or 63 A rating on an RCCB indicates the maximum continuous current its contacts can carry. An RCCB contains no thermal or magnetic overcurrent release; if 60 A flows through a 40 A RCCB without an earth fault, it will not trip and its contacts may overheat. Every RCCB must be backed up by an appropriately rated miniature circuit breaker or upstream breaker.
Why does a standard Type AC RCCB nuisance-trip or lock up on a VFD circuit?
EMC filter capacitors inside variable frequency drives (VFDs) leak high-frequency capacitive currents to earth, causing nuisance tripping on standard 30 mA Type AC breakers. Conversely, a DC bus-to-earth fault produces smooth DC current that saturates a Type AC core so it fails to trip during a real fault. Type F or Type B RCCBs are designed for these waveforms.
Which RCCB type is mandatory for electric vehicle (EV) charging stations?
Under IEC 60364-7-722, AC EV charging points must be protected against smooth DC residual currents above 6 mA from the vehicle's on-board charger either by a Type B RCCB or by a Type A 30 mA RCCB combined with an internal 6 mA DC residual current monitoring device (RDC-DD).