Siemens 3TF47 22-OXMO AC Contactor – 3TF Series SIRIUS Classic

Siemens 3TF47 22-OXMO: Heavy-Duty AC Contactor for High-Power Motor Switching in Industrial Control Circuits

The Siemens 3TF47 22-OXMO is a three-pole AC contactor belonging to the SIRIUS Classic 3TF Series, designed for switching and controlling three-phase AC motors up to 75 kW at 400 V. Within a motor control circuit, this contactor functions as the primary power-switching element between the upstream protective device — typically a 3RV or 3VF motor circuit breaker — and the motor terminals. Its role is deterministic: on receipt of a control signal, the electromagnetic coil energizes, the armature closes against the fixed core, and the three main contacts bridge the load circuit in under 20 ms. On de-energization, the return spring forces contact separation, extinguishing the arc across the silver-alloy contact faces within the arc chute chambers.

The -OXMO suffix designates a variant supplied without a factory-fitted coil, intended for field installation of customer-specified coil voltage modules. This architecture allows procurement of a single mechanical frame for deployment across multiple control voltage standards — 24 V DC, 110 V AC, 230 V AC — without stocking separate part numbers per voltage. The coil module snaps into the lower housing and is retained by a locking tab; replacement requires no tools beyond a flat-blade screwdriver.

The 3TF47 frame accommodates 2 NO + 2 NC auxiliary contacts in the integrated auxiliary contact block, providing feedback signals for PLC digital inputs, interlocking logic in reversing or star-delta starter assemblies, and status indication circuits. The auxiliary contacts are rated at 10 A / 690 V AC (AC-15) and 10 A / 110 V DC (DC-13), covering the full range of conventional control circuit voltages.

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Technical Parameters

Hardware Logical Analysis

The 3TF47 22-OXMO is built on a double-break main contact geometry: each of the three poles contains two contact gaps in series, so the total arc voltage across a single pole at interruption is distributed across two arc chutes rather than one. At 150 A AC-3 duty, this halves the energy density per arc chute, reducing contact erosion rate and extending electrical endurance beyond what a single-break design of equivalent frame size could achieve.

Electromagnetic core design: The E-I laminated core is constructed from cold-rolled silicon steel with a stacking factor above 0.95, minimizing eddy-current losses and reducing coil heating during continuous energization. The shading ring — a short-circuited copper band embedded in the fixed core face — generates a phase-shifted flux component that prevents the 50/60 Hz AC armature from fully releasing between half-cycles, eliminating the characteristic 100/120 Hz mechanical hum that degrades contact pressure consistency in unshaded designs.

EMC and interference suppression: The coil module interface includes a varistor suppression circuit across the coil terminals, clamping inductive kick voltage to below 1.5× supply voltage on de-energization. This protects adjacent PLC output cards from transient overvoltages that would otherwise couple through the control wiring. For DC coil variants, an integrated freewheeling diode in the coil module limits the reverse EMF spike to the diode forward voltage drop (~0.7 V), making the 3TF47 compatible with transistor output modules rated as low as 30 V breakdown.

Contact material and pressure: Main contacts use a silver-cadmium oxide (AgCdO) or silver-tin oxide (AgSnO₂) alloy, selected for resistance to contact welding under high inrush currents typical of AC-3 motor starting (6–8× Ie). The contact spring mechanism maintains a minimum contact force of 12 N throughout the wear life, ensuring stable contact resistance below 100 µΩ per pole even at end-of-life contact thickness.

Modular auxiliary contact block: The 2 NO + 2 NC auxiliary block is mechanically linked to the main armature via a positive-drive actuator pin, not a spring-loaded follower. This means auxiliary contact state is a direct mechanical consequence of armature position, eliminating the possibility of auxiliary contacts indicating a closed state while main contacts remain open due to spring fatigue — a failure mode present in some competing designs.

System Integration Benefits

• Direct IEC 60947-4-1 compliance: The 3TF47 22-OXMO is type-tested to IEC 60947-4-1 Category AC-3, meaning its rated operational current and endurance figures are verified under standardized test conditions, not extrapolated from derating curves. Panel builders can use published coordination tables directly without additional calculation.
• Coordination with Siemens 3RV/3RB protective devices: Siemens publishes Type 2 coordination tables pairing the 3TF47 with 3RV2 motor circuit breakers and 3RB3 solid-state overload relays. Type 2 coordination guarantees that under short-circuit conditions, neither the contactor nor the overload relay sustains damage requiring replacement — only contact cleaning may be needed, reducing MRO downtime.
• Star-delta starter compatibility: The 3TF47 frame is dimensionally and electrically matched to the 3TF40–3TF56 range, allowing three-contactor star-delta assemblies to be built with identical frame sizes. Mechanical interlocking bridges (3TF68) mount directly between adjacent contactors without additional hardware.
• PLC interface determinism: The 2 NC auxiliary contacts provide a hardwired feedback path to PLC digital inputs independent of the coil control signal. This allows the PLC program to detect contact weld conditions (coil de-energized but NC contact not closed) within one scan cycle, enabling predictive maintenance alerts before a welded contactor causes a process fault.
• Coil voltage flexibility via OXMO architecture: A single 3TF47 22-OXMO frame can be configured for 24 V DC, 48 V AC, 110 V AC, 230 V AC, or 400 V AC by installing the corresponding coil module. This reduces spare-parts inventory to one mechanical SKU per frame size, with coil modules stocked separately — a significant advantage for multi-voltage plant environments.
• DIN rail and screw mounting: The housing accepts both EN 60715 DIN rail snap-on mounting and direct screw mounting via integrated M5 fixing holes, accommodating both standard MCC panel layouts and custom enclosure designs without adapter plates.
• Thermal derating transparency: Siemens publishes derating curves for the 3TF47 at ambient temperatures above 40 °C. At 60 °C, the AC-3 current rating derate to approximately 120 A, still sufficient for most 55 kW motor applications. This published data allows engineers to verify thermal margins without empirical testing.
• Diagnostics via auxiliary contact monitoring: In systems using Siemens ET 200 distributed I/O or S7 PLCs with diagnostic-capable modules, the auxiliary contact feedback can be mapped to a diagnostic address, generating automatic fault messages in the HMI with timestamp and contactor identity — reducing fault localization time from minutes to seconds.

Quality Assurance & Global Logistics

Every Siemens 3TF47 22-OXMO unit dispatched from our Xiamen, China facility is a genuine Siemens-manufactured component sourced through verified supply channels. Each unit undergoes a four-stage incoming inspection: label and date-code authentication against Siemens batch records, housing integrity check for cracks or resin voids, coil resistance measurement (where coil is fitted), and auxiliary contact continuity verification across all four auxiliary poles.

Units are packed in anti-static foam inserts within double-wall corrugated cartons, with silica gel desiccant packs to maintain internal humidity below 40% RH during sea or air transit. Each shipment is accompanied by a commercial invoice, packing list, and our inspection report. Certificate of conformance and original Siemens documentation are provided where available for the specific production lot.

Logistics from Xiamen port: DHL Express (2–4 business days to Europe/North America), FedEx International Priority (3–5 days), and sea freight consolidation for bulk orders. Export documentation including HS code classification, CITES/RoHS declarations, and country-of-origin certificates are prepared in-house, eliminating customs clearance delays caused by incomplete paperwork.

A 12-month warranty covers defects in materials and workmanship from the date of shipment. Warranty claims are processed within 5 business days of receipt of the returned unit, with replacement or credit issued upon confirmation of the defect.

Contact Information

Email: [email protected]
WhatsApp: +86 18359268345
Web: siemensplc.com
Location: Xiamen, China
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