🔹 Earth Fault Monitoring Relay, 85–270V AC/DC Auxiliary Supply, 2 C/O Contacts, 35mm Module – 7UG0861-1BU20

Product Description

The Siemens 7UG0861-1BU20 is a SIRIUS digital earth fault monitoring relay (EFR) designed for monitoring earth leakage and fault currents in single-phase 2-wire, 3-phase 3-wire and 3-phase 4-wire electrical systems. It operates with a wide 85–270 V AC/DC control supply and provides 2 changeover contacts (2 C/O) for alarm and trip/control functions. The compact 35 mm module design makes it suitable for installation in electrical control panels and industrial automation systems.

The relay works together with a compatible Siemens 7UG0991 series Core Balance Current Transformer (CBCT). For a 3-phase 3-wire system, L1, L2 and L3 are passed through the CBCT, while for a 3-phase 4-wire system, L1, L2, L3 and Neutral are passed through it. The protective earth conductor must not pass through the CBCT.

The 7UG0861-1BU20 provides adjustable fault-current trip settings from 10% to 80% of the rated current and a configurable trip time delay of 0–99.9 seconds. LED indication provides information about pre-alarm and fault/trip conditions, making the relay useful for monitoring and maintenance of industrial electrical systems.

Key Features

• Brand: Siemens

• Product Family: SIRIUS

• Part Number: 7UG0861-1BU20

• Product Type: Digital Earth Fault Monitoring Relay

• Function: Earth Fault / Earth Leakage Monitoring

• System Compatibility: 1Ø 2-Wire, 3Ø 3-Wire, 3Ø 4-Wire

• Number of Outputs: 2 C/O

• Contact Configuration: 2 Changeover Contacts

• Control Supply: 85–270 V AC/DC

• Module Width: 35 mm

• Trip Current Setting: 10–80% of rated current

• Trip Time Delay: 0–99.9 seconds

• Compatible CBCT Current Ranges: 160 A, 250 A, 630 A

• Power Consumption: Approx. 4 VA

• Operating Temperature: 0°C to +50°C

• LED Indication: Pre-Alarm and Fault/Trip

• Installation: Electrical control panels / DIN-rail type module applications

• CBCT Accessory Series: Siemens 7UG0991

• Standards: IEC 60947-5-1, IEC 60947-4-1

Applications

The Siemens 7UG0861-1BU20 digital earth fault relay is suitable for:

• Earth leakage monitoring

• Earth fault protection systems

• 3-phase 3-wire systems

• 3-phase 4-wire systems

• Industrial electrical panels

• Motor control panels

• Distribution boards

• Industrial automation systems

• Electrical control cabinets

• Machine control panels

• Power distribution systems

• Industrial machinery

• Motor feeders

• Transformer feeders

• Generator systems

• Pump control panels

• Factory automation equipment

• Electrical maintenance systems

Benefits

• Digital monitoring of earth fault current

• Supports both 3-wire and 4-wire three-phase systems

• Wide 85–270 V AC/DC supply range

• Two changeover relay outputs

• Adjustable earth-fault trip threshold

• Adjustable trip time delay up to 99.9 seconds

• Compact 35 mm module

• Compatible with multiple CBCT current ranges

• Pre-alarm and fault/trip LED indication

• Suitable for industrial control panels

• Helps identify earth leakage conditions

• Supports preventive electrical maintenance

• Suitable for motor and power distribution applications

• Flexible installation for different electrical system configurations

• Genuine Siemens SIRIUS monitoring relay

Working Principle

The 7UG0861-1BU20 monitors residual/earth fault current through a compatible Core Balance Current Transformer (CBCT). The conductors of the protected circuit are passed through the CBCT so that an imbalance caused by current flowing to earth can be detected.

For a 3-phase 3-wire system, L1, L2 and L3 are routed through the CBCT. For a 3-phase 4-wire system, L1, L2, L3 and N are routed through the CBCT. The earth conductor must remain outside the CBCT.

When the detected fault current reaches the configured threshold, the relay can provide a pre-alarm or fault/trip output depending on the configured conditions and time delay.

Compatible CBCT Options

The relay is designed to work with Siemens 7UG0991 Core Balance Current Transformers:

• 7UG09910: CBCT 160 A, 3P

• 7UG09911: CBCT 160 A, 4P

• 7UG09912: CBCT 250 A, 3P

• 7UG09913: CBCT 250 A, 4P

• 7UG09914: CBCT 630 A, 3P

• 7UG09915: CBCT 630 A, 4P

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Frequently Asked Questions

Q1. What is Siemens 7UG0861-1BU20?
It is a digital earth fault monitoring relay from the Siemens SIRIUS 7UG0 range.

Q2. What systems does 7UG0861-1BU20 support?
It supports 1-phase 2-wire, 3-phase 3-wire and 3-phase 4-wire systems.

Q3. What is the supply voltage?
The relay operates from 85–270 V AC/DC.

Q4. How many output contacts are available?
It provides 2 changeover contacts (2 C/O).

Q5. What is the module width?
The unit has a compact 35 mm module width.

Q6. What is the earth-fault trip range?
The fault-current setting can be configured from 10% to 80% of the rated current.

Q7. What is the adjustable trip delay?
The trip time delay can be configured from 0 to 99.9 seconds.

Q8. Which CBCTs are compatible?
Compatible Siemens CBCT options cover 160 A, 250 A and 630 A, with 3P and 4P versions.

Q9. What is the function of the CBCT?
The CBCT detects residual current/imbalance associated with an earth fault and provides the sensing signal to the earth fault relay.

Q10. Can it be used in a 3-phase 3-wire system?
Yes. For a 3-phase 3-wire system, L1, L2 and L3 are passed through the CBCT.

Q11. Can it be used in a 3-phase 4-wire system?
Yes. For a 3-phase 4-wire system, L1, L2, L3 and Neutral are passed through the CBCT.

Q12. Should the earth conductor pass through the CBCT?
No. Siemens specifically states that the earth must not pass through the CBCT.

Q13. Does the relay provide LED indication?
Yes. The relay provides LED indication for conditions including pre-alarm and fault/trip.

Q14. What is the power consumption?
The specified power consumption is approximately 4 VA.

Q15. What is the operating temperature range?
The specified operating temperature is 0°C to +50°C.

Q16. Is 7UG0861-1BU20 a circuit breaker?
No. It is an earth fault monitoring relay that provides relay outputs for alarm/control functions.

Q17. Where is this earth fault relay used?
It can be used in industrial panels, motor feeders, power distribution systems, automation panels, machine control systems and electrical equipment.

Q18. What standards are associated with the relay?
The operating instructions identify IEC 60947-5-1 and IEC 60947-4-1 for the device.

Q19. What is the advantage of adjustable trip delay?
Adjustable delay allows the protection response to be coordinated with the application and can help distinguish transient conditions from persistent earth faults.

Q20. Where can I buy Siemens 7UG0861-1BU20 in India?
The Siemens SIRIUS 7UG0861-1BU20 digital earth fault monitoring relay can be sourced from industrial electrical and automation suppliers, subject to current stock and availability.