Schneider Electric MT25N1 Air Circuit Breaker – Masterpact MT Series

Schneider Electric MT25N1 250A 3P Air Circuit Breaker — Masterpact MT Series: Control Loop Architecture and Overcurrent Protection Logic

The Schneider Electric MT25N1 is a 250 A, three-pole air circuit breaker belonging to the Masterpact MT family, a product line engineered specifically for low-voltage main and sub-main distribution boards where precise overcurrent discrimination, high short-circuit breaking capacity, and deterministic trip response are non-negotiable. Unlike molded-case circuit breakers that rely on bimetal thermal elements for overload detection, the MT25N1 is designed to accept Micrologic electronic trip units, shifting protection logic from passive thermal mechanics to active digital signal processing. This architectural decision has direct consequences for system behavior: trip thresholds become software-configurable, protection curves are reproducible across the full operating temperature range, and fault event data can be logged for post-incident analysis.

In a typical low-voltage distribution board (LVDB) topology, the MT25N1 occupies the incomer or bus-coupler position, where it must coordinate upstream with medium-voltage protection relays and downstream with outgoing MCCBs or MCBs. The breaker’s 50 kA rated short-circuit breaking capacity at 415 V AC (Icu per IEC 60947-2) provides the fault-clearing headroom required in industrial facilities fed from transformers with high prospective fault currents. The three-pole configuration covers standard three-phase 400/415 V AC distribution without a neutral pole, making it appropriate for TN-S and TT earthing systems where the neutral is separately protected or not switched.

Real-time Stock & RFQ: [email protected] | WhatsApp: +86 18359268345

Technical Parameters

Hardware Logical Analysis

Stored-Energy Spring Mechanism: The MT25N1 uses a charged-spring operating mechanism that decouples the closing energy source from the trip event. Once the spring is charged — either manually via the charging handle or via an optional motor mechanism — the closing operation is instantaneous and independent of operator force. This eliminates the variable contact-travel velocity that plagues manually operated breakers and ensures consistent arc-quenching geometry on every close operation. The spring-charged state is visually indicated on the mechanism face, providing a clear pre-operation safety check.

Arc Quenching Chamber Design: The MT25N1 employs a de-ion arc chute with metallic splitter plates arranged at a calculated pitch to subdivide the fault arc into a series of shorter arcs. Each subdivision increases the total arc voltage, which in turn accelerates current zero crossing and limits the let-through energy (I²t) to the downstream installation. At 50 kA Icu, the arc chute geometry is optimized to handle the magnetic pressure generated by fault currents without deformation of the splitter stack, maintaining consistent breaking performance across the rated breaking capacity range.

Electronic Trip Unit Interface (Micrologic Compatibility): The breaker’s trip unit cradle accepts Micrologic 2.0 (basic LSI protection), 5.0 (LSI + ground fault), and 6.0 (LSI + ground fault + earth leakage) modules. Each Micrologic unit communicates with the breaker’s shunt trip coil via a direct mechanical latch release, with no intermediate relay required. The Micrologic 5.0 and 6.0 variants additionally support Modbus RTU communication via an optional communication module, enabling remote readout of load current (per phase), trip cause, and cumulative energy consumption — data that feeds directly into power management systems such as EcoStruxure Power.

EMC Design and Auxiliary Contact Isolation: Auxiliary contacts (OF, SD, SDE) are housed in a shielded compartment physically separated from the main current path. This spatial separation, combined with the use of gold-flashed contact surfaces on low-current auxiliary circuits, prevents capacitive coupling of high-frequency transients generated during arc interruption from corrupting the logic-level signals on the auxiliary wiring. In installations with long cable runs to PLCs or SCADA I/O cards, this isolation is critical for preventing nuisance faults on digital input modules.

Thermal Derating and Altitude Compensation: The MT25N1’s rated current of 250 A is specified at 40 °C ambient within an enclosure. Schneider Electric’s published derating curves for the Masterpact MT series indicate a current reduction of approximately 0.5% per °C above 40 °C. At installations above 2,000 m altitude, dielectric strength derating applies per IEC 60947-1 Annex A, and the user must verify that the rated insulation voltage (750 V) remains adequate after altitude correction. These derating parameters are deterministic and documented, allowing system designers to size the breaker with engineering precision rather than empirical margin.

System Integration Benefits

• Selective Coordination with Downstream Devices: The Micrologic trip unit’s configurable short-time delay (tsd) allows the MT25N1 to remain closed during downstream fault clearance, preserving supply continuity to healthy feeders. Time-current discrimination can be verified using Schneider Electric’s EcoStruxure Power Design software, which models the full protection cascade from the MT25N1 incomer to the final MCB.
• Zone Selective Interlocking (ZSI): When paired with Micrologic 5.0 or 6.0 trip units, the MT25N1 supports ZSI wiring between upstream and downstream breakers. Under a bus fault, the downstream breaker signals the upstream device to trip instantaneously rather than waiting for the short-time delay to expire, reducing fault energy let-through by up to 80% compared to non-ZSI schemes.
• Withdrawable Chassis Option: The MT25N1 is available in a withdrawable version that allows the breaker to be racked out to the test or disconnected position without de-energizing the busbar. This enables live maintenance of the trip unit, auxiliary wiring, and secondary injection testing without a planned outage — a significant operational advantage in 24/7 process industries.
• Motor Mechanism for Remote Operation: An optional motor charging and closing mechanism (MCH + XF coil) converts the MT25N1 into a remotely operable switching device. Combined with the MX shunt trip coil, the breaker can be integrated into automatic transfer switch (ATS) schemes or SCADA-controlled load shedding sequences with response times under 100 ms from command issuance to contact closure.
• Metering and Power Quality Data via Micrologic: Micrologic 5.0 and 6.0 trip units provide true RMS current measurement on all three phases with ±1% accuracy, plus voltage, frequency, power factor, active/reactive power, and harmonic distortion (THD) readout. This eliminates the need for a separate power meter at the incomer position, reducing panel wiring complexity and panel real estate.
• Diagnostics Transparency via Ready LED and Fault Memory: The Micrologic unit retains the last trip cause in non-volatile memory (overload, short-circuit, ground fault, or earth leakage), accessible via the front display or Modbus register. This fault memory survives auxiliary power loss, enabling post-trip root cause analysis without reliance on external event recorders.
• Standardized Accessory Ecosystem: The MT25N1 shares a common accessory platform with the broader Masterpact MT range (160 A to 630 A). Undervoltage releases (MN), shunt trips (MX), auxiliary contacts (OF/SD/SDE), and communication modules are interchangeable across frame sizes, simplifying spare parts inventory management for facilities operating multiple Masterpact MT breakers.
• IEC 60947-2 Category B Selectivity: The MT25N1 achieves Category B selectivity per IEC 60947-2, meaning it can coordinate with upstream devices at the full rated short-circuit current without requiring a higher-rated upstream breaker. This allows tighter upstream-downstream current ratio selection and reduces the cost of the upstream protection device in cascaded distribution architectures.

Quality Assurance & Global Logistics

Every MT25N1 unit supplied by siemensplc.com is sourced directly from Schneider Electric’s authorized distribution network. Each breaker ships with its original Schneider Electric factory packaging, including the product label bearing the full catalog reference, serial number, and manufacturing date code. Before dispatch, our technical team performs a visual inspection and verifies the catalog reference against the customer’s purchase order to eliminate part-number substitution errors — a common source of field failures in the secondary market.

Our warehouse is located in Xiamen, Fujian Province, China — a major logistics hub with direct access to Xiamen Gaoqi International Airport and Xiamen Port, both of which operate daily freight services to major industrial destinations in Southeast Asia, the Middle East, Europe, and the Americas. Standard export packaging for the MT25N1 uses anti-static foam inserts within a double-wall corrugated carton, rated for the mechanical shock and vibration levels specified in IEC 60068-2-27 and IEC 60068-2-6 respectively. For time-critical projects, air freight with DHL Express or FedEx International Priority is available, with typical transit times of 3–5 business days to most destinations. Sea freight via LCL consolidation is available for bulk orders where lead time permits.

All shipments are accompanied by a commercial invoice, packing list, and certificate of origin (CO) issued by the Xiamen Chamber of Commerce. For customers requiring additional documentation — such as a material test report, third-party inspection certificate, or customs pre-clearance documentation — these can be arranged upon request at the time of order placement. The 12-month warranty covers manufacturing defects under normal operating conditions as defined in IEC 60947-2. Warranty claims are processed with a target response time of 48 hours from receipt of the defective unit.

Contact Information

Email: [email protected]
WhatsApp: +86 18359268345
Web: siemensplc.com
Location: Xiamen, China
© 2026 siemensplc.com. All rights reserved.