Thermal Overload

A vital protective device that monitors motor current and automatically disconnects power if the motor begins to overheat, preventing costly winding damage.

Siemens | SIRIUS 3RU21 Thermal Overloads

Siemens SIRIUS 3RU21 relays are designed for high-reliability motor protection under normal starting conditions (Class 10). They are mechanically and electrically optimized to plug directly into the bottom of SIRIUS 3RT contactors, creating a “compact starter” that saves significant rail space.

SIRIUS 3RU21

Model Number: 3RU2116-1HB0

Class 10 tripping; phase failure sensitivity; temperature compensation (-40°C to +60°C).

Key Technical Specifications:

  • Features an integrated differential slider that ensures the relay trips faster if one phase fails, preventing motor damage from unbalanced loads.

  • Includes a mechanical “Trip” flag and a TEST function that allows you to simulate a trip to verify that your control wiring is correct.

  • A dedicated STOP button opens the NC auxiliary contact to switch off the contactor, but unlike a trip, it doesn’t require a full reset period.

SIRIUS 3RB3

Model Number: 3RB3036-2WW1

Electronic version; wider setting ranges (1:4); Class 10, 20, or 30 selectable.

Key Technical Specifications:

  • A dedicated STOP button opens the NC auxiliary contact to switch off the contactor, but unlike a trip, it doesn’t require a full reset period.

  •  Includes a mechanical “Trip” flag and a TEST function that allows you to simulate a trip to verify that your control wiring is correct.

  • Features an integrated differential slider that ensures the relay trips faster if one phase fails, preventing motor damage from unbalanced loads.

Schneider Electric | TeSys™ LRD

The Schneider TeSys LRD is likely the most widely used thermal overload relay in the world. It is sourced for its “multi-standard” design and its incredible versatility in mounting. Whether you need a standard Class 10 or a heavy-duty Class 20 for long motor startups, the LRD range has a specific SKU.

TeSys LRD

Model Number: LRD08

Class 10A and Class 20 options; differential tripping; IP20 “Finger-safe” terminals.

Key Technical Specifications:

  • Features a blue toggle that lets you choose between Manual Reset (operator must press a button) or Auto Reset (the relay resets itself once it cools down).

  • The current adjustment dial is protected by a clear, lockable cover, preventing unauthorized personnel from “turning up” the current to stop nuisance trips.

  • Models above 40A use patented EverLink technology, which uses a spring-loaded system to maintain constant pressure on the cables, even as the copper “creeps” over time.

TeSys Deca (New)

Model Number: LRD16

Modernized version of LRD; improved environmental data; multi-standard screw terminals.

Key Technical Specifications:

  • Models above 40A use patented EverLink technology, which uses a spring-loaded system to maintain constant pressure on the cables, even as the copper “creeps” over time.

  • Features a blue toggle that lets you choose between Manual Reset (operator must press a button) or Auto Reset (the relay resets itself once it cools down).

  • The current adjustment dial is protected by a clear, lockable cover, preventing unauthorized personnel from “turning up” the current to stop nuisance trips.

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