Schneider Electric LRD21 TeSys Deca Overload Relay 12-18 A

LRD21 TeSys Deca thermal overload relay: what it is and how the code reads

The LRD21 is a Schneider Electric product described in the datasheet as: TeSys Deca, thermal overload relay, 12 to 18 A, class 10A. The LRD family is the TeSys Deca differential thermal overload relay line, fitted below a contactor to protect a motor against sustained overcurrent and phase loss. Seven Star LLC supplies the LRD21 in Oman and the GCC as an independent supplier based in Muscat.

Decoding the reference: LRD is the TeSys Deca thermal overload relay series and the number (21) selects the current setting band; for this reference the datasheet gives an adjustment range of 12 to 18 A with Class 10A IEC 60947-4-1. A relay in a neighbouring band has a different range, so select the band so that the motor full-load current falls in the upper half of the setting range where possible.

Technical specifications of the LRD21

How the LRD21 protects the motor

A thermal overload relay uses bimetallic elements heated by the motor current. When the current stays above the set value long enough, the elements bend and operate the auxiliary contacts, which open the contactor coil circuit. The LRD21 is a differential type, which means it also trips faster when the phase currents are unbalanced; the datasheet states for phase failure: Tripping current 130 % of Ir on two phase, the last one at 0.

The trip class describes how quickly the relay trips under a standard overload multiple. The datasheet states Class 10A IEC 60947-4-1 for the LRD21. Class 10A suits normal starts; motors with long run-up times such as large fans or high-inertia loads can trip nuisance-wise on a class 10A relay and need a slower class or an electronic relay.

Where the LRD21 fits in a starter

The LRD21 is mounted directly under a compatible contactor; the datasheet lists compatibility with LC1D32; LC1D18; LC1D25; LC1D38. The 95/96 NC contact is wired into the contactor control circuit and the 97/98 NO contact signals the trip to a PLC. Red stop and blue reset push-buttons are fitted on the front as listed in the datasheet.

Related bands in the same family include LRD08, LRD10, LRD14, LRD32, which cover successive current ranges. Use the datasheet of the exact reference to check that the contactor frame and the setting range suit the motor.

Selection and ordering checklist for the LRD21

• Set the dial to the motor full-load current from the nameplate; the LRD21 covers 12 to 18 A.
• Check that the contactor is among those the datasheet lists (LC1D32; LC1D18; LC1D25; LC1D38).
• Confirm trip class (Class 10A IEC 60947-4-1) against the motor start time.
• Decide on manual or automatic reset policy in the control circuit.
• Check conductor size against the listed terminal capacity and torque, and the operating temperature range -20 to 60 °C without derating IEC 60947-4-1.
• If heavy starting or sensitive protection is needed, consider an electronic overload relay instead.

Installation, commissioning and maintenance of the LRD21

Mount the relay on the contactor lower terminals, tighten the power terminals to the torque in the datasheet and set the current dial. Test the trip and reset function once before commissioning with the test button. The device is 45 mm (W) x 66 mm (H) x 70 mm (D) and weighs 0.124 kg, so it fits easily in a standard starter row.

During operation, a relay that trips often is giving a signal: check the motor load, the supply voltage balance and ambient temperature before raising the setting. Do not increase the dial above the motor rating to avoid trips. Inspect terminals at planned shutdowns and keep the front window clean so the dial setting can be read.

Typical applications of the LRD21 in Oman and the GCC

The LRD21 protects pumps, fans, compressors and conveyors in motor control centres in oil and gas facilities, water and wastewater works, desalination units and industrial plants across Oman and the GCC. In hot switchrooms the ambient compensation range in the datasheet, -20 to 60 °C, is relevant when checking the setting.

Information to send with an RFQ for the LRD21

• Full reference LRD21 and quantity
• Motor full-load current and voltage
• Contactor reference it will be mounted under
• Required trip class and reset method
• Delivery location and timing

Documents and quotation

A datasheet for this product is attached on this page. It lists the electrical, mechanical and environmental data summarised above.

Send us the part number, quantity and application and we will confirm availability and a quotation. Seven Star LLC is an independent supplier in Muscat and does not represent itself as an official channel of the manufacturer.