ABB SACE TMAX T4 N 250 Molded Case Circuit Breaker with RC222/4 Trip Unit

The ABB SACE TMAX T4 N 250 is a high-performance molded case circuit breaker (MCCB) belonging to the Tmax series, designed for main distribution and motor protection in industrial, commercial, and infrastructure applications. This breaker has a frame size of 250 Amperes and is equipped with an electronic trip unit model RC222/4, which provides adjustable overload and short-circuit protection for four poles (3-phase + neutral). The combination is identified by the catalog number 54954. The Tmax T4 series is known for its compact dimensions, high breaking capacity, and modular accessories, making it a popular choice for switchgear manufacturers and panel builders worldwide.

Electrical Specifications

The T4 N 250 frame is rated for a nominal current (In) of up to 250 A. The RC222/4 trip unit can be set for a current rating (Ir) over a range typically from 0.4 to 1 times In, allowing the breaker to be matched to specific load requirements. The interrupting capacity (Icu) for the N version at 415 V AC is generally 36 kA (depending on exact voltage rating and standard), suitable for many industrial distribution boards. The breaker can be used in systems up to 690 V AC. The RC222 trip unit provides electronic thermal-magnetic protection: the overload (L) protection is adjustable with a time delay (long time) and inverse time characteristic; the short-circuit (S) protection (short time delay) is adjustable; and the instantaneous (I) protection has a fixed threshold. The trip unit also includes an earth fault protection option, but the RC222 variant covers L, S, and I protections only. The four-pole configuration (4P) means the breaker has switching and protection on all three phases and the neutral pole (fully rated or reduced neutral depending on the order code).

RC222 Electronic Trip Unit

The RC222 is a microprocessor-controlled trip unit that replaces traditional thermal-magnetic elements with precise electronic sensing. It offers better selectivity and coordination with downstream devices. The user can adjust the following parameters: Protection L (overload) with pickup current Ir from (0.4 to 1) x In and time delay t1 (typically 3 to 18 seconds at 6 x Ir). Protection S (short-time) with pickup current Isd adjustable (typically 2 to 10 x Ir) and time delay tsd (0.1 to 0.5 seconds). Protection I (instantaneous) with pickup Ii fixed (usually 10 to 12 x In). The trip unit also features a thermal memory function that simulates the heating and cooling of the protected cable, adding an additional safety margin during repeated short-circuits. An LED indicator on the front of the trip unit shows the cause of the trip (L, S, or I). The RC222 operates from internal current transformers and requires no auxiliary power, ensuring tripping even when the circuit is under fault conditions.

Mechanical Design and Accessories

The T4 N 250 has a compact footprint, allowing more breakers to be installed in a given panel width. The breaker has a fixed version (non-drawout) but can be mounted on a DIN rail or using screws. It features a rotary handle mechanism with ON and OFF positions clearly indicated. The breaker can be equipped with various accessories: shunt trip release, undervoltage release, auxiliary contacts (1NO+1NC), alarm contacts, rotary external handles (door-mounted), and motor operators for remote switching. The terminals accept copper cables or busbars. The RC222 trip unit can be fitted with a communication module (Modbus RTU) for remote monitoring of currents, trip status, and settings, integrating the breaker into an energy management system.

Installation and Usage Recommendations

When installing the T4 N 250 breaker, ensure correct orientation (vertical is standard, but horizontal mounting is allowed with possible derating). The line and load connections must be made with appropriate torque values specified on the breaker label. For four-pole breakers, it is essential to confirm whether the neutral pole is switched (fully rated) or solid, depending on the application (e.g., for systems requiring neutral switching due to harmonic content). The ambient temperature for use is -25 to +70 degrees Celsius, with derating applied above 40 degrees Celsius. The breaker is compliant with IEC 60947-2 and UL 489 standards, thus suitable for international projects. In motor protection applications, the RC222 can be set to match the motor’s thermal curve, eliminating the need for a separate overload relay in some configurations.

Maintenance and Testing

Periodic inspection of the breaker includes checking for signs of overheating (discoloration), dust accumulation, and proper mechanical operation of the handle. The RC222 trip unit can be tested using a primary injection test set to verify pickup accuracy. Some versions have a test button that simulates a trip condition to confirm that the mechanism operates. The breaker’s contacts may wear over time, and after several short-circuit interruptions, the breaker should be replaced. Spare parts such as terminals and accessories are available from ABB. The trip unit’s settings should be recorded on the label or in the electrical documentation for future reference.