IEC 62423: Type F and Type B Residual Current Operated Circuit-Breakers

IEC 62423, first published in 2007 with a corrigendum in 2011, specifies the requirements for Type F and Type B residual current operated circuit-breakers (RCDs) functionally independent of, or functionally dependent on, line voltage. This standard addresses a critical gap in protection technology as modern electrical installations increasingly incorporate power electronic converters that generate non-sinusoidal and DC residual currents. Traditional Type A and Type AC RCDs, designed for sinusoidal AC and pulsating DC waveforms, are unable to reliably detect certain types of fault currents produced by variable frequency drives (VFDs), photovoltaic inverters, and electric vehicle charging stations. Without appropriate DC-sensitive RCD protection, installations face elevated risks of electric shock, fire, and equipment damage from undetected residual currents that can saturate the sensing core of conventional devices and render them completely inoperative.

Operating Characteristics and Classification

IEC 62423 defines two distinct RCD types with progressively broader detection capabilities. Type F RCDs detect residual sinusoidal AC currents at power frequency, pulsating DC currents (with or without 0.006 A DC ripple), and composite residual currents with frequencies up to 1 kHz from phase-controlled rectifiers and frequency converters. The key distinction from Type A is the ability to operate correctly when the residual current contains mixed-frequency components, which is typical in circuits supplying switched-mode power supplies, single-phase VFDs, and induction cooktops. Type F devices must also maintain their tripping characteristics in the presence of superimposed smooth DC currents up to 10 mA, which would otherwise saturate the sensing transformer in lower-type devices.

Type B RCDs offer the most comprehensive protection and detect all forms of residual currents: sinusoidal AC up to 2 kHz, pulsating DC, smooth (pure) DC, and composite currents generated by three-phase rectifiers and inverters. The standard specifies that Type B RCDs must trip within the standard residual operating current (IΔn) limits even when the residual current consists entirely of smooth DC. This capability is critical for protecting circuits fed through three-phase rectifiers such as those found in large VFDs, UPS systems, EV fast chargers, and industrial motor drives. The operating time requirements follow the same categories as standard RCDs: instantaneous (without intentional delay, typically 30-40 ms), S-type (selective/short-time delayed), and adjustable-time-delay versions for specific applications.

Test Methods and Performance Verification

The standard specifies a comprehensive suite of type tests to verify the correct operation of Type F and Type B RCDs under complex residual current conditions. The most distinctive among these is the composite residual current test, where the RCD is subjected to a mixture of AC, pulsating DC, and smooth DC components simultaneously. For Type B devices, the smooth DC test requires verification of tripping at IΔn between 0.5 and 1.0 times the rated residual current when the current is pure DC with a maximum ripple content of 5%. This test is conducted at both positive and negative polarity to ensure symmetrical behavior. The test current must be applied at a controlled rate of rise, typically not exceeding 0.5IΔn per second, to simulate realistic fault current development and verify proper operation of the detection algorithm.

Frequency response testing is another crucial element. Type F RCDs must be tested at multiple frequencies between the power frequency (50/60 Hz) and 1 kHz, with the tripping current not exceeding 1.5 times the rated IΔn at any test frequency. The test points specified in the standard include the fundamental frequency (50 or 60 Hz), the 3rd harmonic (150 or 180 Hz), the 5th harmonic (250 or 300 Hz), the 10th harmonic (500 or 600 Hz), and an upper frequency point of 1 kHz. Type B devices additionally require testing at frequencies up to 2 kHz and under 3-phase rectifier waveform conditions that produce composite ripple currents with characteristic harmonics (typically 300 Hz and 600 Hz for 6-pulse rectifiers operating from a 50 Hz supply). The standard also requires a 10% overcurrent test to verify that the RCD does not exhibit nuisance tripping during brief surge currents, such as those caused by capacitive intrush currents at equipment start-up.

Engineering Design Insights for Modern Installations

From a system design perspective, the selection and placement of Type F and Type B RCDs require careful consideration of the load characteristics, the distribution system architecture, and the applicable regulatory framework. For electric vehicle charging installations, most national regulations now mandate Type B or Type B+ RCD protection for AC charging stations above 3.6 kW, and for all DC fast-charging stations, due to the risk of smooth DC fault currents from the on-board charger rectifier stage. Even for Mode 2 and Mode 3 AC charging at lower power levels, where Type A RCDs may be permitted, many designers opt for Type B RCDs as a best practice to ensure comprehensive protection and future-proofing against evolving load characteristics.

For photovoltaic systems, the presence of DC-AC inverters creates the potential for both AC and DC residual currents on the AC side. Type B RCDs are required for all grid-tied PV installations in many jurisdictions, as inverter faults can generate smooth DC residual currents that would blind conventional RCDs. The leakage current from PV inverter EMC filters, typically in the range of 30-300 mA at the power frequency, must also be considered to avoid nuisance tripping. This often necessitates the use of RCDs with higher IΔn values (e.g., 100 mA or 300 mA) for the PV supply circuit, combined with Type B selectivity through strategic time-delay coordination with downstream Type A RCDs at 30 mA for socket-outlet circuits. Coordination charts in IEC 62423 provide guidance on achieving selectivity between Type B upstream and Type F or Type A downstream devices, based on the ratio of their rated residual operating currents and the intentional time delay of the upstream device.

In industrial environments with variable frequency drives, the common-mode voltage generated by the PWM switching scheme produces high-frequency leakage currents through the parasitic capacitance of motor cables and windings. These leakage currents, typically containing significant energy at the inverter switching frequency (2-16 kHz) and its harmonics, require Type B+ RCDs or special-purpose detection algorithms for reliable discrimination between normal leakage and dangerous fault conditions. The standard recommends that for VFD applications, an RCD should be selected with a rated residual current of at least 3 times the expected maximum leakage current under normal operating conditions. For installations with multiple VFDs on the same RCD-protected circuit, the cumulative leakage current and spectral composition must be carefully analyzed, often requiring the use of specialized current transformers and electronic processing circuits capable of distinguishing between the characteristic frequency signatures of normal operating leakage and genuine fault currents.