Microelettrica Scientifica PTC1177

Working Principle

1. PTC thermistor embedded inside motor stator windings changes resistance sharply once winding temperature exceeds safe threshold
2. PTC1177 internal precision reference circuit continuously measures thermistor loop resistance
3. When resistance exceeds factory calibrated trip threshold (2700Ω standard), internal solid-state relay contact opens to cut motor control circuit
4. Independent auxiliary alarm contact closes simultaneously to trigger local audible alarm or remote PLC fault signal
5. Built-in temperature hysteresis circuit prevents rapid on-off cycling after cooling down; manual reset button for fault lockout mode
6. Galvanic isolation separates low-voltage PTC sensor loop and high-voltage motor control contact circuits

Full Technical Specification Parameters

• Power Supply Voltage: 24 VDC / 230 VAC dual universal control supply options
• PTC Thermistor Trip Resistance Threshold: 2700 Ω ±10% standard calibration
• Reset Hysteresis Resistance: 1100 Ω auto-reset threshold; manual lockout reset button selectable
• Thermistor Loop Wiring Resistance Tolerance: Max 300Ω total cable resistance without trip drift
• Main Protection Contact Rating: 250 VAC / 6 A normally closed trip contact
• Auxiliary Alarm Contact Rating: 250 VAC / 3 A normally open fault signal contact
• Response Time: ≤200ms after PTC resistance exceeds trip threshold
• Operating Temperature Range: -25°C ~ +70°C ambient cabinet temperature
• Protection Class: IP20 DIN rail housing
• EMC Compliance: EN 61000-6-2 industrial environment immunity standard
• Mechanical Life: 10 million switching cycles without contact degradation
• Electrical Life: 100,000 cycles under rated contact load

Material & Structural Design

1. Housing Body: Flame-retardant V0 grade PA66 insulating plastic
2. Internal Circuit Board: SMD component FR4 PCB with conformal coating for moisture resistance
3. Switching Contacts: Silver tin oxide alloy anti-welding contact material
4. Mounting Base: Standard 35mm DIN rail clip integrated to rear housing
5. Front Panel: Manual reset push button, red overheat fault LED indicator, wiring terminal screw blocks
6. Terminal Covers: Transparent dustproof plastic shroud for touch safety

Core Functional Characteristics

1. Direct interface with 3-phase motor embedded PTC temperature sensors, monitors stator winding hot spot temperature
2. Dual contact outputs: main safety trip contact for motor stop circuit, auxiliary alarm contact for remote fault notification
3. Selectable auto-reset or manual lockout reset mode for different process safety requirements
4. Wide dual control supply voltage supports both DC 24V safety circuits and AC 230V standard control panels
5. High wiring resistance tolerance for long-distance motor PTC sensor cable routing
6. Fast sub-second trip response prevents motor insulation burnout from locked rotor or overloading
7. Compact narrow DIN rail housing minimizes control cabinet space occupation

Application Industry Scenarios

• Three-phase asynchronous pump, fan, blower motor thermal overload protection
• Compressor, extruder, conveyor drive motor winding overheat monitoring
• HVAC central air conditioning large fan motor safety protection
• Water treatment plant submersible pump thermal fault cut-off system
• Mining, cement plant heavy-duty induction motor protection circuits

DIN Rail Installation Requirements

1. Clip unit onto standard 35mm TS35 DIN rail horizontally, no vertical inverted mounting
2. Maintain minimum 10mm spacing between adjacent relays for heat dissipation
3. Separate low-voltage PTC sensor wiring from high-current motor power wiring with ≥10cm routing gap
4. Torque terminal screws to 0.8–1.0 N·m to avoid loose contact heating
5. Mount inside IP54 minimum rated control cabinet to prevent dust and liquid ingress

Operation & Maintenance Precautions

1. Only connect certified motor PTC thermistor sensors; NTC thermistors cannot be used with this model
2. Do not extend PTC sensor cable with thin-gauge wire to avoid total loop resistance exceeding 300Ω
3. Test trip function quarterly by applying variable resistance decade box to simulate overheat condition
4. If frequent tripping occurs, inspect motor winding insulation and cooling fan operation first
5. Do not install near high-temperature power resistors or servo drive heat sinks to avoid ambient overheating
6. Disconnect control supply voltage before modifying internal wiring terminal connections