Siemens 3RN2010-1CA30 SIRIUS 3RN2 Thermistor Motor Protection Relay

Overview

The Siemens 3RN2010-1CA30 is a thermistor motor protection relay from the SIRIUS 3RN2 range. Siemens describes it as a compact evaluation unit in a 17.5 mm enclosure with screw terminals, one NO contact and one NC contact, a control supply voltage of 24 V AC/DC, automatic reset, suitability for bimetallic switches, two LEDs for ready and tripped status, and electrical separation. Its job is to watch temperature sensors built into a motor winding and to open the motor control circuit when the winding becomes too hot, which protects the motor in situations that a current-based overload relay cannot see. Siemens lists the product lifecycle of the Siemens 3RN2010-1CA30 as active.

Seven Star LLC supplies the Siemens 3RN2010-1CA30 and other SIRIUS control components to panel builders, motor control centre suppliers and plant maintenance teams across the Sultanate of Oman and the GCC. Our Muscat team checks control voltage, contact arrangement and reset behaviour against the Siemens data sheet with the buyer, and we hold engineering support in Muscat for motor protection devices.

Operating Principle of the Siemens 3RN2010-1CA30

As general engineering background, thermistor motor protection works with PTC sensors embedded in the stator winding by the motor manufacturer. A PTC thermistor has a low resistance at normal temperature and a resistance that rises very steeply once its rated response temperature is reached. The evaluation relay passes a small measuring current through the sensor circuit connected to its T1 and T2 terminals, and when the resistance rises above its response threshold the relay trips. Because the sensor sits inside the winding, this method reacts to the real winding temperature whatever the cause: high ambient temperature, blocked cooling air, heavy starting duty, single phasing or frequent switching.

When the Siemens 3RN2010-1CA30 trips, its output contacts change state and the tripped LED lights, so the NC contact can open the contactor coil circuit and the NO contact can signal the fault to a PLC or alarm panel. With automatic reset, the relay returns to normal once the winding has cooled and the sensor resistance has fallen again. Siemens also states that the unit is suitable for bimetallic switches, which are thermal contacts embedded in some motor windings instead of PTC sensors. The data sheet shows no error memory, no external reset and no manual reset for this compact version.

Engineering Design of the Siemens 3RN2010-1CA30

The Siemens 3RN2010-1CA30 is 17.5 mm wide, 100 mm high and 90 mm deep, and it mounts on a 35 mm DIN rail by snap-on fixing or by screws, in any position. Siemens specifies zero clearance to neighbouring devices and to grounded or live parts, so several relays can be mounted side by side. Screw terminals accept solid conductors of 0.5 to 4 mm² or finely stranded conductors with end sleeves of 0.5 to 4 mm², AWG 20 to 12, at a tightening torque of 0.6 to 0.8 N·m, and the terminals for the auxiliary and control circuit are removable. Net weight is about 104 g.

The control supply is 24 V AC at 50 and 60 Hz or 24 V DC, with an operating range of 0.85 to 1.1 times the rated value. Inrush current peaks at 1.8 A for 2 ms, power loss is 0.4 W, and the relay rides through a supply interruption of at least 40 ms. Output contacts use AgSnO2 material and are rated 3 A at AC-15 250 V and 1 A at DC-13 24 V, protected by a 6 A DIAZED fuse. Insulation voltage is 300 V for overvoltage category III and pollution degree 3, and surge voltage resistance is 4 kV.

Key Features

The Siemens 3RN2010-1CA30 offers these features for motor protection:

• Direct winding temperature monitoring with PTC thermistors catches overheating that current measurement alone may miss.
• A narrow 17.5 mm enclosure saves space in motor control centres and drive panels.
• One NO and one NC contact give a trip function and a separate signal output.
• Automatic reset restores the circuit after the winding has cooled down.
• Ready and tripped LEDs show the status at a glance during commissioning and fault finding.
• Galvanic isolation separates the input from the output and the outputs from each other.
• Siemens quotes a typical mechanical life of 10 million operating cycles and 100,000 cycles at AC-15.
• Operation is specified from -25 to +60 °C, with storage and transport from -40 to +85 °C.

Industrial Applications

Thermistor relays are used wherever motors face conditions that make current-based protection unreliable. Typical cases are motors fed from variable frequency drives running at low speed, where the shaft-mounted fan cools poorly, pumps and fans with frequent starts, motors in high ambient temperatures, and machines with blocked or dusty cooling paths. The Siemens 3RN2010-1CA30 is normally combined with a contactor and a circuit breaker or overload relay, so that winding temperature and motor current are both supervised.

In Oman, high summer temperatures and dust make winding temperature protection particularly relevant for pumping stations, cooling towers, conveyors at quarries and cement plants, and HVAC fans in Muscat and Sohar. Seven Star LLC supplies the Siemens 3RN2010-1CA30 alongside related devices such as the ABB TA25DU6.5 thermal overload relay, the Pilz PNOZ s3 compact safety relay and the Siemens CPU 1214C compact PLC that can read the relay’s signal contact.

Selection Notes within the SIRIUS 3RN2 Range

The SIRIUS 3RN2 range includes compact units like the Siemens 3RN2010-1CA30 and standard evaluation units in 22.5 mm enclosures. Siemens lists, for example, the 3RN2010-1BA30, a standard evaluation unit with two changeover contacts, 24 V AC/DC supply and auto reset. Buyers who need manual or remote reset, fault memory, other control voltages or spring-loaded terminals should choose a different 3RN2 order number. Before ordering a replacement, compare the full order code on the existing relay and the type of sensor fitted in the motor, PTC thermistor or bimetallic switch, with the Siemens data sheet.

Technical Specifications

The table below summarises the Siemens 3RN2010-1CA30 data from the Siemens product data sheet:

How to Order

To order the Siemens 3RN2010-1CA30, send Seven Star LLC the quantity and, for replacements, a photo of the existing relay label, and our team in Muscat will prepare a formal quotation. The Siemens product data sheet can be downloaded from this page, and we provide engineering support in Muscat for the Siemens 3RN2010-1CA30 and other SIRIUS devices for customers across Oman and the GCC.