Product Description

Siemens SIRIUS Thermistor Motor Protection Relay, 110–240V AC/DC, 2 CO, PTC Sensor, Auto/Manual/Remote Reset - 7UG0881-1BU20

Product Description

The Siemens 7UG0881-1BU20 is a SIRIUS thermistor motor protection relay designed to monitor the winding temperature of motors and generators using PTC thermistor sensors. It detects abnormal temperature rise and provides a fast protective response to help prevent motor winding damage caused by overheating. The relay operates with a wide 110–240 V AC/DC control supply and provides 2 changeover (2 CO) relay outputs for motor control, alarm and protection circuits.

The relay supports single and triple PTC sensors and can identify different sensor conditions including sensor healthy, sensor trip, sensor open and sensor short. The device offers selectable Auto and Manual operating modes, with remote reset capability, making it suitable for a wide range of industrial motor protection applications.

The 7UG0881-1BU20 has an instantaneous trip response and LED indications for power, sensor and relay status. Its compact design and 110–240 V AC/DC control supply make it suitable for motor control panels, pumps, fans, compressors, generators, industrial machinery and automation systems.

Key Features

• Brand: Siemens

• Product Family: SIRIUS 7UG

• Part Number: 7UG0881-1BU20

• Product Type: Thermistor Motor Protection Relay

• Protection Method: PTC Thermistor Sensor

• Control Supply: 110–240 V AC/DC

• Frequency: 50/60 Hz

• Output: 2 CO

• Sensor Type: PTC

• PTC Compatibility: Single and Triple PTC Sensors

• Reset: Auto / Manual / Remote

• Trip Response: Instantaneous

• Initialization Time: Less than 3 seconds

• Relay Mode: Failsafe / Non-Failsafe selectable

• Operating Temperature: 0°C to +50°C

• Maximum Power Consumption: 3 VA

• Rated Output Relay Current: 5 A at AC-12

• Protection Degree: IP20

• LED Indication: Power ON, Sensor and Relay

• Sensor Detection: Healthy / Trip / Open / Short

• Rated Insulation Voltage: 300 V AC

• Product Lifecycle: PM300 – Active Product

Applications

The Siemens 7UG0881-1BU20 thermistor motor protection relay is suitable for:

• Motor winding temperature protection

• Three-phase motor protection

• Electric motor overheating protection

• Generator winding protection

• Pump motor protection

• Fan motor protection

• Compressor motor protection

• Industrial machinery

• Motor control panels

• MCC panels

• Industrial automation systems

• Conveyor systems

• HVAC motor applications

• Machine control cabinets

• Industrial drives

• OEM motor control systems

• Electrical control panels

• Preventive motor protection

Benefits

• Protects motors against abnormal winding temperature

• Uses reliable PTC thermistor sensing

• Supports single and triple PTC sensor configurations

• Wide 110–240 V AC/DC control supply

• Two changeover relay outputs

• Instantaneous trip response

• Auto, manual and remote reset options

• Selectable failsafe and non-failsafe operation

• Detects PTC sensor short and open conditions

• LED indication for operating and fault status

• Compact Siemens SIRIUS monitoring solution

• Suitable for motors and generators

• Helps reduce overheating-related motor failures

• Suitable for industrial automation and control panels

• Genuine Siemens motor protection relay

Sensor Monitoring

The relay continuously evaluates the resistance of the connected PTC sensor circuit. Siemens specifies the following operating conditions:

• Sensor Short: ≤ 40 Ω

• Sensor Healthy: ≥ 44 Ω (±3) to < 3.8 kΩ (±150)

• Sensor Trip: ≥ 3.8 kΩ (±150) to < 5.5 kΩ (±150)

• Sensor Open: ≥ 5.5 kΩ and above

• Sensor Recovery / Cut-in / Reset: ≤ 1.5 kΩ (±60)

When the motor cools and the PTC resistance reaches the recovery condition, the relay can reset automatically when Auto mode is selected. In Manual mode, reset can be performed manually or through the remote reset input.

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Frequently Asked Questions

Q1. What is Siemens 7UG0881-1BU20?
It is a Siemens SIRIUS thermistor motor protection relay used to monitor motor or generator winding temperature through PTC sensors.

Q2. What is the control supply voltage?
The relay operates with a 110–240 V AC/DC control supply at 50/60 Hz.

Q3. What type of sensor does this relay use?
The relay uses PTC thermistor sensors installed in the motor winding.

Q4. Does 7UG0881-1BU20 support single and triple PTC sensors?
Yes. Siemens specifies compatibility with both single and triple PTC sensor configurations.

Q5. How many output contacts are available?
The relay provides 2 changeover contacts (2 CO).

Q6. What reset options are available?
The relay supports Auto, Manual and Remote reset.

Q7. Does the relay provide instantaneous motor protection?
Yes. The specified trip response is instantaneous when the PTC sensor reaches the trip condition.

Q8. What happens when the PTC sensor detects excessive temperature?
When the PTC resistance reaches the defined sensor trip range, the relay enters the trip condition and can operate its output contacts to initiate the required motor protection/control action.

Q9. Can the relay detect a damaged PTC sensor?
Yes. It can identify both sensor short-circuit and sensor open-circuit conditions, in addition to healthy and trip states.

Q10. Where is Siemens 7UG0881-1BU20 commonly used?
It is suitable for industrial motors, generators, pumps, fans, compressors, MCC panels, motor control panels, machinery and industrial automation systems.