Residual Current Circuit Breaker ABB FH204 AC-25/0.03 25 A 4P

ABB FH204 AC-25/0.03 is a 4-pole residual current circuit breaker that combines overcurrent protection with earth-leakage detection in a single device. Rated for 25 A and with a 30 mA AC-type residual current sensitivity, this unit protects TN and TT electrical systems by interrupting supply in case of overload, short circuit or dangerous leakage currents. The compact four-pole design simplifies protection of three-phase circuits with neutral, offering both person-protection against electric shock and basic fault isolation for residential and light commercial installations.

Advantages

The ABB FH204 AC integrates magnetic and thermal overcurrent protection with a residual current detector, reducing the need for separate devices and simplifying installation. AC-type sensitivity detects sinusoidal alternating leakage currents, while the 30 mA trip threshold balances safety for persons with immunity to common transient disturbances. The four-pole construction provides coordinated protection for three-phase circuits including neutral, and the device is designed for DIN-rail mounting and straightforward wiring in standard distribution boards.

Suitable for

• Protection of three-phase (3P+N) circuits in residential buildings
• Small commercial or light industrial distribution boards
• Circuits requiring both overcurrent and 30 mA earth-leakage protection
• Applications with TN and TT earthing systems

When it may not be suitable

This ABB FH204 AC device is AC-type and therefore detects sinusoidal alternating residual currents; it may not provide reliable protection against pulsating DC or smooth DC leakage currents produced by some electronic equipment or EV chargers. For installations where DC residual currents are possible, a device with A or B type sensitivity should be considered. Also, the 25 A rating must match the circuit conductor sizing and load requirements; higher continuous currents require a device with a larger rated current.

Key specifications

• Poles: 4 (three-phase + neutral)
• Rated current: 25 A
• Residual trip sensitivity: 30 mA (AC type)
• Function: Combined overcurrent (MCB) and residual current (RCD) protection
• Installation: DIN-rail mounting, modular form factor for distribution boards

How to use

Install the ABB FH204 AC-25/0.03 on a standard 35 mm DIN rail in the distribution board, ensuring correct orientation and secure terminal connections for all four conductors. Connect incoming supply to the line terminals and load circuits to the load terminals, observing proper torque for screws and manufacturer wiring recommendations. After installation, verify correct operation by performing a functional test using the device test button or an external RCD tester, and confirm that the device trips at the expected conditions before placing the circuit into service.

What to consider before purchase

• Compatibility with the installation earthing system (TN or TT)
• Whether AC-type residual current sensitivity is sufficient for connected equipment
• Circuit rated current and conductor sizing relative to the 25 A rating
• Available space on DIN rail and distribution board layout

Usage recommendations

Use the ABB FH204 AC-25/0.03 for combined circuit and personal protection in three-phase installations where leakage currents are predominantly sinusoidal. Schedule periodic testing of the residual current function and verify connections during routine maintenance to ensure ongoing protection performance.