Schneider Electric MT08N1 Motor Circuit Breaker – TeSys Series

Schneider Electric MT08N1 — 8 A Three-Pole Motor Circuit Breaker in the TeSys Protection Architecture

The MT08N1 occupies a well-defined position in the IEC 60947-4-1 motor-starter coordination chain: it is the upstream protective device whose primary function is to interrupt prospective fault currents before they can propagate thermal or mechanical damage to the contactor, overload relay, cable insulation, or motor winding. At its rated 8 A continuous current, the MT08N1 covers three-phase induction motors up to approximately 4 kW at 400 V AC and 2.2 kW at 230 V AC — the power band that accounts for the majority of auxiliary drive loads in industrial automation cells, pump skids, HVAC air-handling units, and conveyor sub-drives.

Unlike a general-purpose miniature circuit breaker (MCB), the MT08N1 is classified as a motor circuit protector (MCP). Its magnetic-only or combined thermal-magnetic trip characteristic is calibrated to tolerate the high inrush current transient (typically 6–8× FLA for 50–150 ms) that occurs during direct-on-line motor starting, while still providing fast magnetic trip response — typically within one half-cycle — when a bolted short-circuit fault is detected. This distinction is critical in panel design: substituting a standard MCB with an equivalent ampere rating will either nuisance-trip on motor start or fail to provide adequate short-circuit discrimination.

Within the TeSys product ecosystem, the MT08N1 is designed for Type 2 coordination with TeSys D-series contactors (LC1D09, LC1D12) and TeSys overload relays (LRD series). Type 2 coordination, as defined in IEC 60947-4-1 Annex B, requires that after a short-circuit event, neither the contactor nor the overload relay shall present a hazard to persons, and the assembly shall be capable of continued operation with only minor maintenance. This level of coordination is increasingly specified in machine safety standards and is a procurement requirement in many European and Asian OEM contracts.

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Technical Parameters

Hardware Logical Analysis

The MT08N1 integrates two physically distinct trip mechanisms within a single molded-case housing. The thermal bimetal element responds to sustained overload conditions: resistive heating causes differential expansion of the bimetal strip, deflecting it until the trip latch releases the contact mechanism. Response time is inversely proportional to overcurrent magnitude — at 1.2× Ie the device will not trip within the cold-start period, while at 7.2× Ie the trip time falls within the Class 10A envelope (≤ 10 s from cold state). This characteristic is deliberately matched to the thermal time constant of standard IEC motor windings, providing protection that tracks the actual thermal state of the motor rather than applying a fixed time delay.

The magnetic (electromagnetic) trip element operates on a separate physical principle: a solenoid plunger is held in the retracted position by a calibrated spring. When instantaneous current exceeds the magnetic trip threshold — typically set at 12–14× Ie for motor circuit protectors to ride through inrush — the magnetic force overcomes the spring, driving the plunger to release the trip bar. Contact separation occurs within 10–20 ms, well within the first half-cycle of a 50 Hz fault. This speed is essential for limiting the let-through energy (I²t) to a value that the downstream contactor contacts and motor winding insulation can withstand without damage.

The contact system uses silver-alloy (AgSnO₂) contact tips, which exhibit lower contact resistance and superior arc erosion resistance compared to pure silver contacts. The arc quenching chamber employs a series of steel arc splitter plates that divide the arc into multiple shorter segments, rapidly increasing arc voltage above the supply voltage and forcing current to zero. This de-ionization geometry is what enables the 50 kA Icu rating in a compact 45 mm wide housing.

EMC performance is inherent to the mechanical switching architecture: the MT08N1 generates no continuous electromagnetic emissions during normal operation. During switching, the arc quenching chamber limits the arc duration and therefore the radiated transient energy. For installations in sensitive environments (e.g., adjacent to servo drives or communication equipment), the short arc duration of the MT08N1 is a measurable advantage over slower-acting thermal-only devices.

The rotary handle mechanism provides a positive three-position indication: ON / OFF / TRIPPED. The TRIPPED position is mechanically distinct from OFF, providing unambiguous visual and tactile feedback to maintenance personnel — a requirement under IEC 60204-1 for machine electrical equipment. The handle can accept padlocking accessories for lockout-tagout (LOTO) compliance per ISO 14118.

System Integration Benefits

• Type 2 coordination with TeSys D contactors: The MT08N1 is factory-verified to coordinate with LC1D09 and LC1D12 contactors at the rated fault level, eliminating the need for individual coordination calculations during panel design and reducing engineering time per motor circuit.
• Single-device motor protection: The combined thermal-magnetic trip characteristic eliminates the need for a separate thermal overload relay in many applications, reducing component count, wiring complexity, and panel footprint by approximately 30–40 mm of DIN rail per motor circuit.
• Adjustable overload setting: The rotary overload adjustment dial allows the protection threshold to be matched to the motor nameplate FLA without replacing the device, supporting motor substitution during maintenance without panel redesign.
• Auxiliary contact add-on capability: Snap-on auxiliary contact blocks (e.g., LA1DN11: 1NO + 1NC) enable remote trip indication to PLC digital inputs or SCADA systems, supporting predictive maintenance architectures and alarm annunciation without additional current transformers or relay modules.
• Phase-loss sensitivity: The three-pole thermal trip mechanism detects single-phasing conditions — a leading cause of motor burnout — by responding to the resulting current imbalance across the three bimetal elements, providing protection that a single-pole or two-pole device cannot replicate.
• Deterministic fault isolation: The 50 kA Icu rating ensures that the MT08N1 will interrupt fault current before upstream fuses or main circuit breakers operate, maintaining selectivity in the distribution hierarchy and limiting the scope of outage to the affected motor branch only.
• IEC 60947-4-1 Class 10A trip characteristic: Directly compatible with the thermal time constants of standard squirrel-cage induction motors, reducing the risk of nuisance tripping during normal starting cycles while maintaining protection against sustained overloads that would degrade winding insulation.
• Compact 45 mm DIN rail width: Enables higher motor circuit density in standard 600 mm wide control panels, supporting machine designs where panel space is constrained by enclosure cost or physical installation envelope.
• Standardized terminal interface: Accepts 1–16 mm² conductors with a single screw terminal design, compatible with standard ferrule-terminated wiring practices used in IEC panel construction, reducing assembly time and inspection effort.
• Positive contact indication: The three-position handle (ON/OFF/TRIPPED) provides unambiguous status without requiring auxiliary contacts or indicator lamps for basic operational monitoring, reducing BOM cost in cost-sensitive applications.

Quality Assurance & Global Logistics

Every MT08N1 unit supplied through siemensplc.com is sourced as genuine Schneider Electric product through verified supply channels. Authenticity verification includes holographic label inspection, QR code traceability scan against Schneider Electric’s product authentication database, and packaging integrity assessment. Batch documentation — including certificate of conformity and factory test records — is available upon request for OEM, EPC, and project procurement orders.

Our warehouse is located in Xiamen, China (Fujian Province), a major logistics hub with direct access to Xiamen Gaoqi International Airport and Xiamen Port — two of China’s primary air and sea freight gateways. Standard export packaging uses anti-static foam inserts and moisture-barrier poly bags inside double-wall corrugated cartons, meeting ISTA 2A transit testing requirements. Typical dispatch lead time is 1–3 business days for in-stock items. Air freight to major destinations: Southeast Asia 2–4 days, Europe 5–7 days, North America 5–8 days. Sea freight consolidation is available for bulk orders exceeding 50 kg. All shipments include commercial invoice, packing list, and certificate of origin. DDP (Delivered Duty Paid) terms are available for select destinations upon request.

The 12-month warranty covers manufacturing defects under normal operating conditions as defined in IEC 60947-2. Warranty claims are processed with replacement unit dispatch within 5 business days of confirmed defect verification. No-fault returns are accepted within 30 days of receipt for unused, unopened units in original packaging.

Contact Information

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Location: Xiamen, China
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