Schneider Electric LRD325 TeSys 17-25 A Overload Relay

LRD325: 17 to 25 A class 10A overload relay in plain terms

The LRD325 is a Schneider Electric product listed in the datasheet as: TeSys LRD thermal overload relays – 17 to 25 A – class 10A. In a motor starter it is the part that watches the current of the motor and opens the control circuit when an overload or a lost phase would otherwise overheat the windings. Seven Star LLC supplies the LRD325 in Oman and the GCC as an independent supplier based in Muscat.

Reading the reference: the datasheet identifies the LRD325 as part of the TeSys LRD family, and the title gives the figure that matters, namely the adjustable window of 17 to 25 A with thermal class 10A. It is built as the large frame (55 mm wide, EverLink BTR power connectors) used with LC1D40A to LC1D65A contactors. The 17 to 25 A range on this larger frame is intended for motors drawing between 17 and 25 A, driving pumps, compressors, cooling-water fans and conveyors. The larger body carries EverLink BTR connectors on the power side.

Technical specifications of the LRD325

Fitting the LRD325 to a TeSys starter

The datasheet lists the contactors compatible with the LRD325 as LC1D40A, LC1D50A, LC1D65A. The mounting options are plate, with specific accessories; rail, with specific accessories; under contactor. In practice the relay plugs straight under a TeSys Deca contactor of the listed frames, so the contactor and relay together form a compact direct-on-line or reversing starter without extra wiring in the power circuit.

The relay body measures 55 mm wide, 70 mm high and 123 mm deep and weighs 0.375 kg. It belongs to the large frame (55 mm wide, EverLink BTR power connectors) used with LC1D40A to LC1D65A contactors. A relay of the same range on the smaller frame exists in the TeSys LRD family, but the contactor list here points to LC1D40A, LC1D50A and LC1D65A, so match the frame to the contactor you actually have.

Typical applications of the LRD325 in Oman and the GCC

The large frame is found in motor control centres and process panels where the motors are heavier, the cables are thicker and the EverLink connectors make torque-checked connections practical. In Oman and the GCC such starters appear in water and desalination plants, oil and gas auxiliaries, power station balance-of-plant and building services.

Heat and dust are the main enemies. Overload relays are temperature-compensated, but a hot, dusty panel still ages terminals and contacts faster, so inspect the connections of the LRD325 during planned shutdowns and keep the front cover and dial clean.

Trip threshold and phase-loss behaviour of the LRD325

The setting dial of the LRD325 covers 17 to 25 A. The datasheet gives the tripping threshold as 1.14 ± 0.06 Ir conforming to IEC 60947-4-1, which means the relay is built to trip when the motor current reaches about 1.14 times the dialled value, with a tolerance of 0.06 times. At the top of the scale, 1.14 times 25 A works out to about 28.5 A; at the bottom of the scale, 1.14 times 17 A is about 19.38 A.

The relay is also a differential type. For the phase failure case, the datasheet states a tripping current of 130 % of Ir on two phases while the third carries nothing, which at 25 A corresponds to about 32.5 A in the two live phases. This sensitivity is what protects a three-phase motor from running on two phases after a blown fuse or a loose terminal, and it is the reason the type is chosen over a simple thermal element for pumps and fans.

Class 10A is the common choice for motors that start quickly. Under IEC 60947-4-1 the class number is the longest tripping time in seconds at 7.2 times the setting current, so a class 10A relay reacts faster to a locked rotor than a class 20 relay. The relay has temperature compensation over -20 to 60 °C, so the setting does not drift within that band.

Selection checklist for the LRD325

• Motor nameplate current: it must sit between 17 and 25 A, ideally in the middle of the dial.
• Contactor: the starter must use one of LC1D40A, LC1D50A, LC1D65A.
• Trip class: this relay is class 10A; confirm that it suits the starting time of the load.
• Signalling circuit: the contact is rated 0.95 A at 380 V AC-15 for signalling circuit; 0.06 A at 440 V DC-13 for signalling circuit.
• Space: allow 55 mm x 70 mm x 123 mm and a weight of 0.375 kg.
• Status: say whether you need a spare for an existing starter or a new installation.

Where the LRD325 sits in the LRD ladder

The table below places the LRD325 between its neighbours by current range, using the datasheet data of each reference. It helps when the nameplate current falls near a boundary or when the contactor decides the frame.

Commissioning and maintenance of the LRD325

Set the dial of the LRD325 to the nameplate current of the motor, not to the contactor rating. Press the red stop push-button to confirm that the contactor drops, then use the blue reset push-button to restore the relay. The relay should be checked after any short-circuit event, because a short-circuit protective device is still needed upstream; the overload relay does not replace it.

For spares, keep the same reference rather than guessing from the range, because the frame and the terminals differ between the compact, large and largest groups. If you need a relay for a different current, send us the contactor reference and the nameplate current and we will confirm the correct member of the family.

Information to send with an RFQ for the LRD325

• Full reference LRD325 and the quantity required
• Motor nameplate current, voltage and power
• Contactor reference the relay will be fitted to
• Required delivery location and timing
• Whether it is a spare, a replacement or a new installation

Documents and quotation

A datasheet for this product is attached on this page. It lists the electrical, mechanical and environmental data summarised above, and it is the document to check against your own drawings.

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 is not affiliated with the manufacturer.