Schneider Thermal Overload Relay LRD3357

Schneider Electric LRD3357 Thermal Overload Relay — Industrial-Grade Thermal Motor Protection

The Schneider Thermal Overload Relay LRD3357 is a dependable protection device engineered to safeguard mid-range three-phase motors in industrial and commercial electrical systems. Designed as part of Schneider Electric’s TeSys LRD series, this relay helps prevent motor damage caused by prolonged overcurrent, phase loss, or load imbalance — making it an essential component in reliable motor starter assemblies paired with TeSys contactors (such as LC1D80 and LC1D95).

🔌 What Is the Schneider LRD3357 Thermal Overload Relay?

This is a three-pole thermal overload relay with an adjustable current range of 37 – 50 A, engineered to protect motors by detecting excessive current and tripping before overheating causes damage. The LRD3357 continuously monitors all three phases, trips on sustained overloads, and includes features such as phase-failure sensitivity and the option for manual or automatic reset — ensuring enhanced motor protection and control.

🔧 Key Features & Benefits

• Adjustable Thermal Protection (37 – 50 A) — Precisely set the relay to match the full-load current of your motor for accurate protection.

• Class 10A Trip Characteristic — Offers a reliable trip profile that tolerates normal start-up currents yet responds effectively to sustained overloads.

• Three-Pole Monitoring — Ensures all three phases are checked for overload, unbalance, and phase loss conditions.

• Phase Loss & Unbalance Detection — Helps prevent motor failure due to abnormal phase conditions.

• Manual/Automatic Reset & Test Options — Flexibility to reset or test the relay without shutting down the system.

• Auxiliary Contacts (1NO + 1NC) — Provides signalling for control panels and automation systems.

• Secure Screw-Clamp Terminals — Reliable, vibration-resistant connections for power and control wiring.

• Direct Mount or Panel Mount — Can be mounted under compatible contactors or on DIN rails/panels for integration flexibility.

These features make the LRD3357 a versatile and dependable choice for protecting motors operating under medium-load conditions.

📍 Why Choose the LRD3357 Overload Relay?

Industrial three-phase motors often undergo frequent start/stop cycles, overload stress, or phase irregularities — conditions that can cause overheating and winding damage. The Schneider LRD3357 thermal overload relay helps:

• Protect motors from thermal damage and failure

• Minimise unplanned downtime and maintenance costs

• Enhance safety by detecting faults early

• Integrate reliably with Schneider contactor starter systems

This makes it ideal for engineers, electricians, and panel builders prioritising robust motor protection in demanding electrical environments.

📌 Typical Applications

• Motor starter panels with contactors

• Pumps, compressors & industrial machinery

• Conveyor systems and material handling

• HVAC and ventilation motor control

• Electrical control cabinets in factories and commercial buildings

Whether for new installations or upgrades, the LRD3357 enhances reliability and safety across motor control systems.