Schneider Electric LRD350 — Thermal Relay Sizing & Specs Guide

By Abdullah Zahid
18 min read
Schneider Electric LRD350 TeSys Deca thermal overload relay 37-50A Class 10A EVERLINK terminals for TeSys D motor starter

Schneider Electric LRD350 TeSys Deca Thermal Overload Relay: Specs, Sizing & Alternatives Guide

If you have a motor with a nameplate full-load current between 37 and 50 A and you are running a TeSys D contactor in the LC1D40A to LC1D65A range, the Schneider Electric LRD350 is the thermal overload relay your motor starter needs. This Class 10A, 3-pole bimetallic relay with EVERLINK power terminals is a long-proven component in HVAC, pump, and general industrial motor control — and getting the current range, tripping class, and terminal type confirmed before you order is what separates a clean installation from an expensive wrong-part return.

If you have already confirmed this is the right relay for your application, check current pricing and availability for the LRD350 at LeadTime.ca — ships worldwide.

Who Should Buy the LRD350 — and Who Shouldn't

The Schneider Electric LRD350 is the right choice for engineers and technicians specifying or replacing a thermal overload relay for standard 3-phase AC motors with a full-load current in the 37 to 50 A range, paired with a TeSys D contactor.

  • Motor nameplate full-load current (FLA) falls within the 37 to 50 A adjustable range
  • Existing or new contactor is a TeSys D model: LC1D40A, LC1D50A, or LC1D65A
  • Application is a standard industrial motor — squirrel-cage induction, DOL or standard starter, not a high-inrush compressor or crusher
  • Class 10A tripping is appropriate — motor reaches full speed within the startup window without triggering a nuisance trip
  • Installation requires EVERLINK power terminals (confirm this matches your existing contactor before ordering)
  • Control circuit wiring uses a standard 1NO-1NC contact configuration

If your motor draws high locked-rotor current at startup — compressors, crushers, or VFD-driven loads — the LRD360 (Class 20, 48 to 65 A) is the correct choice. If your motor FLA falls between 28 and 40 A, the LRD340 is the right relay. Do not order the LRD350 for TeSys K contactors or the LC1D09 — the mounting interface is incompatible.

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Where the LRD350 Fits in a Motor Starter System

A complete IEC motor starter has three functional layers: the contactor that switches main power to the motor, the thermal overload relay that monitors current and trips on fault, and the control circuit that interprets the relay's trip signal and commands the contactor coil. The Schneider Electric LRD350 occupies the second layer — it is a TeSys Deca thermal overload relay that mounts directly to a TeSys D contactor and continuously monitors all three motor phases.

When motor current exceeds the relay's thermal setting — whether from sustained overload, a stalled rotor, or phase loss — the bimetallic element inside the LRD350 deflects under heat, mechanically opening the trip contact. That break in the control circuit removes the signal from the contactor coil, which drops out and disconnects main power from the motor. The motor de-energizes and is protected from winding damage. The relay can then be reset manually or automatically, depending on how the control circuit is configured.

The LRD350's wide 37 to 50 A adjustment range means a single relay model covers multiple motor sizes on the same production floor — a practical advantage for facilities standardizing on TeSys D infrastructure and trying to minimize the number of unique spare parts in inventory.

Typical System Architecture for TeSys D Motor Starters

The LRD350 sits between the TeSys D contactor and the downstream motor terminals in the signal and power chain. Here is how the typical component stack looks:

  • Upstream disconnect or fuse block — provides isolation and short-circuit protection upstream of the starter
  • TeSys D contactor (LC1D40A, LC1D50A, or LC1D65A) — switches three-phase main power on command from the control circuit
  • LRD350 mounted directly to the contactor — monitors phase current continuously; sends trip signal to the contactor coil on fault
  • Control circuit wiring (1NO-1NC contacts from LRD350) — carries the trip signal to the coil control loop; integrates with PLC input or hardwired stop circuit
  • Motor load — 3-phase AC induction motor; nameplate FLA must fall within the 37 to 50 A adjustment range of the LRD350

Industries and Applications That Rely on the LRD350

The LRD350 appears most frequently in HVAC central plant installations — protecting chiller pump motors, cooling tower fan motors, and air handling unit drives where motor FLA typically falls in the 37 to 50 A range at 400V or 460V. Its Class 10A tripping characteristic suits these loads well because their current draw during startup is predictable and does not produce extended high-inrush transients.

In water and wastewater facilities, the relay is a standard choice for pump station motor starters, protecting aeration and transfer pump drives where undetected overloads could result in burned windings and costly downtime. The phase failure detection capability is particularly valuable in pump applications where a lost phase during operation creates immediate mechanical risk.

OEM equipment builders specifying packaged air handlers, pump skids, or industrial machinery frequently select the LRD350 as a standard across multiple product SKUs when their motor platform falls in the 37 to 50 A range. The wide adjustment dial allows a single part number to cover different motor configurations within the same product family, reducing procurement complexity and spares cost.

Industrial maintenance teams restocking TeSys D starter kits rely on the LRD350 as a shelf-stable MRO component. The 18-month warranty from date of purchase and Schneider Electric's confirmed stocking in distribution facilities support its use as a reliable emergency replacement part.

Application Typical Deployment
HVAC chiller pump motor Paired with LC1D50A contactor; dial set to motor nameplate FLA (typically 42 to 48 A at 460V)
Cooling tower fan drive Direct-on-line starter with LRD350; Class 10A suitable for squirrel-cage fan motors
Water/wastewater pump station Motor starter panel; relay provides phase failure and stall protection in unattended installations
OEM packaged pump skid LRD350 standardized across multiple motor sizes within 37 to 50 A range; simplifies BOM
Industrial conveyor or mixer drive TeSys D starter kit with LRD350; DOL starting; predictable current profile compatible with Class 10A
MRO emergency replacement Technician confirms contactor model and FLA from nameplate; replaces failed relay with matching terminal type

LRD350 Technical Specifications

Specification Value Notes
Current Setting Range 37 to 50 A Adjustable dial; set to motor nameplate FLA
Tripping Class Class 10A Trips within 10 seconds at 1.2x set current
Number of Poles 3 3-phase AC motor protection only
Contact Configuration 1NO-1NC Standard Form A / Form B for TeSys D control circuits
Contact Rating 10 A Trip signal contact only; not rated for main power switching
Supply Frequency 0 to 400 Hz Covers both 50 Hz and 60 Hz industrial installations
Ambient Temperature -20 to +60°C Do not install in environments below -20°C
Enclosure Rating IP20 Protection against finger contact; not sealed against water spray
Terminal Type EVERLINK power terminals Verify compatibility with existing contactor before ordering
Standards Compliance UL 508, CSA C22.2 No. 14, ATEX, CE, RoHS, IEC 60947-4-1, IEC 60947-5-1 Multi-standard certification covers North America, Europe, and international markets

Full technical specifications are available on the product page at LeadTime.ca.

How to Size the LRD350 for Your Motor

Sizing a thermal overload relay correctly comes down to one number: the motor's full-load amperage (FLA) as printed on the motor nameplate. For the LRD350 to be the right relay, that FLA must fall between 37 and 50 A. If it falls below 37 A, the LRD340 (28 to 40 A) is the correct choice. If it exceeds 50 A, the LRD360 (48 to 65 A) is required.

Key steps for correct thermal setting:

  • Locate the motor nameplate and record the full-load current (FLA) in amperes — do not use the motor's kW or HP rating as a proxy
  • Confirm the FLA falls within the 37 to 50 A adjustment range of the LRD350 before ordering
  • After installation, rotate the front-panel dial to the exact FLA value marked on the nameplate — the dial is marked in 1 A increments from 37 to 50
  • Verify the dial index visually before energizing; a setting even 2 to 3 A below actual FLA can cause nuisance trips under normal load
  • If nuisance trips occur at the correct setting, measure actual running current with a clamp meter before adjusting — a confirmed inrush problem may indicate the need to upgrade to a Class 20 relay rather than increasing the thermal setting

For reference, a 37 A thermal setting typically corresponds to motor powers in the 18 to 22 kW range at 400V. A 50 A setting corresponds to approximately 28 to 32 kW at 400V. At 460V/60 Hz, these equivalent power ranges shift upward slightly — a 50 A setting covers motors in the 30 to 37 kW range.

Class 10A Tripping: What It Means and When It Isn't Enough

The tripping class of a thermal overload relay defines how long the relay will wait before tripping when motor current reaches 7.2 times the set current — the standard locked-rotor test condition. Class 10A means the relay trips within 10 seconds under this condition. In practical terms, it also means the relay trips within 10 seconds when current is at 1.2 times the thermal setting, protecting motor windings from sustained overcurrent before thermal damage accumulates.

Class 10A is the correct choice for the majority of standard squirrel-cage induction motors started direct-on-line or through a soft starter with a modest ramp time. HVAC pump motors, fan drives, conveyor motors, and similar loads with predictable startup profiles are ideal Class 10A applications.

Where Class 10A fails is in high-inrush applications. Compressor motors, crushers, centrifuges, and other loads that draw sustained high current for longer than 10 seconds during startup will cause the LRD350 to trip before the motor reaches full speed — not a fault condition, but a mismatch between the relay's protective response and the motor's legitimate startup profile. For these applications, the LRD360 with its Class 20A rating provides the additional startup time without compromising overload protection during running conditions. Class 30 alternatives exist for the most demanding high-inrush cases.

EVERLINK vs. Screw Clamp Terminals: What to Verify Before Ordering

EVERLINK power terminals are a distinguishing feature of the TeSys Deca generation of Schneider relays. Unlike traditional screw clamp terminals that require a calibrated tightening torque of 0.6 to 0.8 Nm and are susceptible to vibration loosening if under-torqued, EVERLINK terminals use a one-turn push-and-twist connection mechanism that eliminates torque specification concerns, speeds up replacement, and reduces the risk of loose connections during service.

The practical implication for buyers is straightforward: if your existing TeSys D contactor uses EVERLINK terminals, order a relay with EVERLINK terminals. If your existing contactor has screw clamp terminals — which is common on units installed before the TeSys Deca transition — confirm that the relay you order matches the terminal type on the contactor. A mismatch here does not produce a hazard, but it produces a part that physically cannot be installed on your existing hardware, and that means a return shipment and downtime extension.

When placing an emergency order, photograph the existing relay's terminal area and include that information in your purchase order or distributor communication. This single step eliminates the most common wrong-part delivery scenario for this product family.

Contactor Compatibility: Which TeSys D Models Work With the LRD350

The LRD350 mounts directly to TeSys D contactors in the 40 A to 65 A range via a snap-fit mounting interface. The three compatible contactor models confirmed by Schneider Electric's published compatibility matrix are the LC1D40A, LC1D50A, and LC1D65A. The relay can also be installed in a stand-alone configuration with a separate terminal block for rail mounting where contactor-mount installation is not possible.

The LRD350 is not compatible with the LC1D25A — the contactor is too small and the thermal relay's current range exceeds the contactor's rating. The LC1D09 belongs to the TeSys K family and uses a different mounting interface entirely; attempting to install an LRD350 on a TeSys K contactor will not produce a secure mechanical connection. No compatibility with contactors from other manufacturers has been established or documented by Schneider Electric.

Contactor Model Compatible Notes
LC1D40A Yes 40 A contactor; suitable pairing for motors at the lower end of the LRD350 range
LC1D50A Yes 50 A contactor; common pairing for standard HVAC motor starters
LC1D65A Yes 65 A contactor; largest compatible contactor for this relay
LC1D25A No Contactor current rating too small for LRD350 range
LC1D09 / TeSys K No Different mounting interface; physical incompatibility
Other manufacturers No Tested and approved only for TeSys D family

LRD350 vs. LRD340 vs. LRD360: Which Relay Do You Actually Need?

The TeSys D thermal relay family spans a wide range of motor sizes. The LRD350 sits in the middle of the commonly used range. If your motor FLA falls outside 37 to 50 A, the relay choice changes — and choosing incorrectly based on nameplate data you haven't verified is the most common and most expensive ordering mistake in this product category.

Feature LRD350 (Class 10A) LRD340 (Class 10A) LRD360 (Class 20A)
Current Range 37 to 50 A 28 to 40 A 48 to 65 A
Tripping Class Class 10A Class 10A Class 20A
Terminal Type EVERLINK / Screw EVERLINK / Screw EVERLINK / Screw
Mounting TeSys D contactor TeSys D contactor TeSys D contactor
Best For Standard HVAC, pump, fan motors; wide adjustment range covers multiple motor sizes Smaller motors; lower-range industrial and pump pre-protection applications High-inrush motors, compressors, crushers; extended startup time without nuisance trips

If your motor FLA is above 50 A, the LRD360 is the correct relay — and if that motor also has high inrush, its Class 20A rating gives the startup time the LRD350 cannot provide. Check current availability and pricing for the LRD350 and related variants at LeadTime.ca.

Expert Verdict on the Schneider Electric LRD350

The LRD350 earns its place as a standard-issue thermal relay in HVAC and industrial motor control because it does its job without complication. For HVAC technicians, maintenance electricians, and OEM equipment builders specifying standard chiller, pump, fan, and conveyor motor starters with FLA in the 37 to 50 A window, this relay is the right tool. The 18-month warranty from date of purchase, Schneider Electric's confirmed distribution stocking status, and the multi-standard certification package covering UL 508, CSA C22.2 No. 14, ATEX, CE, and IEC 60947-4-1 make it a low-risk specification for regulated and non-regulated industrial environments alike. Its wide adjustment range genuinely reduces SKU complexity for facilities running multiple similar motor sizes, and the EVERLINK terminal system removes the torque specification burden that causes problems with screw clamp replacements in the field.

Where the LRD350 falls short is equally clear. High-inrush motors — compressors, crushers, centrifuges, or any load that draws extended locked-rotor current at startup — will cause nuisance trips with a Class 10A relay. The answer is the LRD360 with Class 20A tripping, not a higher thermal setting on the LRD350. Applications requiring electronic overload protection with fast response times, motor current trending, or digital communication back to a PLC or SCADA system need a solid-state electronic relay, not a bimetallic device. Single-phase or DC motor applications are outside the LRD350's design scope entirely — this relay protects 3-phase AC motors only. Buyers needing a single relay to cover a very wide motor range will need multiple models across the TeSys series rather than stretching the LRD350 beyond its 37 to 50 A window.

From a procurement standpoint, the LRD350 is a stable, actively stocked product in the Schneider Electric distribution network — Schneider's own product page confirms normal stocking in distribution facilities, with market-typical lead times of 1 to 2 weeks. For emergency MRO replacements, a specialist industrial distributor's technical staff can verify contactor compatibility and terminal type before the order ships, preventing the wrong-part delivery scenario that causes the most costly downtime in this product category. That vetting step is genuinely worth the call. View current LRD350 pricing and stock status at LeadTime.ca — orders ship worldwide.

For volume pricing, lead time confirmation ahead of a major build, or help verifying the correct relay for a specific motor nameplate, contact the LeadTime.ca team directly — we ship worldwide and can confirm compatibility before your order is placed.

What Engineers Need to Know Before Ordering the LRD350

The Schneider Electric LRD350 is a mature, proven product with decades of field history and a low rate of design-related failures. Unlike newer products that generate active forum discussion as installers work through first-deployment issues, the LRD350 rarely surfaces in technical communities — not because it is obscure, but because it behaves predictably when selected and installed correctly. The problems that do arise with this relay family are almost always specification and ordering errors, not device failures. Understanding those failure modes before the order is placed is the engineering work that prevents downtime.

The most consequential pre-order check is verifying the motor nameplate FLA against the 37 to 50 A adjustment range. A motor running at 36 A full-load current belongs on an LRD340; a motor at 52 A needs an LRD360. Neither situation is served by adjusting the LRD350 dial to its extreme and hoping for margin. The second most consequential check is terminal type. EVERLINK and screw clamp terminals are not interchangeable on the same contactor — a relay ordered with the wrong terminal type will not install, regardless of whether every other specification is correct. In an emergency replacement scenario, that mismatch means extended downtime while the correct part is sourced.

The tripping class question catches buyers less often but causes more damage when it does. A Class 10A relay on a compressor motor that draws 8 to 12 seconds of high inrush at startup will trip reliably and repeatedly, preventing the motor from ever reaching operating speed. Technicians who encounter this behavior sometimes assume the relay is faulty and replace it with an identical part — repeating the failure. The root cause is tripping class mismatch, and the solution is the LRD360 (Class 20A) or a Class 30 alternative for the most demanding inrush profiles. If there is any uncertainty about a motor's startup current behavior, consulting with LeadTime.ca's technical team before ordering is faster than troubleshooting a nuisance trip after installation.

Wiring and Installation Overview

The LRD350 installs directly onto a TeSys D contactor via a snap-fit mounting interface, or stand-alone on a DIN rail with a separate terminal block. For full wiring diagrams and step-by-step installation procedures, refer to Schneider Electric's published installation documentation for the TeSys Deca relay series.

  • Main power connections (L1, L2, L3) use EVERLINK one-turn push-and-twist or screw clamp terminals accepting wire gauge 0.5 to 16 mm² (AWG 20 to 6); do not mix terminal types within the same installation
  • Trip contact terminals (TRI, AUX) use screw clamp only and are rated for low-voltage control circuit signals at 10 A; connect per the control wiring diagram for the TeSys D contactor coil circuit
  • Screw clamp terminals, where used, require tightening torque of 0.6 to 0.8 Nm; under-torqued terminals are a common cause of intermittent faults in high-vibration environments
  • Confirm ambient temperature at the installation location is within the -20 to +60°C operating range before mounting; IP20 enclosure rating means the relay requires installation inside a control panel or enclosure with appropriate protection
  • Set the thermal adjustment dial to the motor's nameplate FLA before energizing; verify the dial index visually and confirm no nuisance trip occurs during the motor's first startup sequence

Wrong-Part Prevention Checklist

Before finalizing your order for the Schneider Electric LRD350, verify each of the following items against your motor nameplate, existing contactor, and installation drawings:

  1. Confirm motor nameplate current falls within 37-50A adjustment range
  2. Verify your contactor is a TeSys D model (LC1D40A, LC1D65A range) — this relay does not work with LC1D09 or TeSys K
  3. Check terminal type on existing installation: are terminals EVERLINK or screw clamp? Ensure new relay matches
  4. Confirm your control circuit requires 1NO-1NC contact configuration (do not assume; check wiring diagram)
  5. Verify AC supply frequency is within 0-400 Hz (standard for 50/60 Hz industrial sites — unlikely issue in North America)
  6. Ensure ambient temperature at installation site is between -20 to +60°C (extreme cold storage or outdoor exposure may violate limits)
  7. Confirm this is a Class 10A application (standard industrial motors with soft-start or DOL starter); high-inrush loads need Class 20+

If any item on this checklist raises a question before you order, contact the LeadTime.ca team — we can verify compatibility against your contactor model and motor nameplate data before the order ships.

Frequently Asked Questions

Does the LRD350 work with the LC1D65A contactor, or is the LC1D50A the maximum compatible model?

The LRD350 is compatible with the LC1D40A, LC1D50A, and LC1D65A contactors — all three are confirmed TeSys D models within the supported range. The LC1D65A is the largest compatible contactor for this relay. The relay mounts directly to any of these three contactors via the standard TeSys D snap-fit interface.

Will the LRD350 cause nuisance trips when starting a motor with a soft starter?

For motors started through a soft starter with a standard ramp-up profile that reaches full speed within the Class 10A trip window, the LRD350 should not nuisance trip under normal operating conditions. However, if the motor has a particularly long ramp time or high locked-rotor current that sustains elevated current beyond 10 seconds at 1.2x the set point, nuisance trips can occur. In that situation, the LRD360 with its Class 20A tripping characteristic is the appropriate relay. Measuring actual starting current with a clamp meter before making that determination is recommended.

What is the difference between manual reset and automatic reset on the LRD350, and which should I use?

Manual reset requires a technician to physically press the reset button on the relay face after a trip event before the motor can be restarted. Automatic reset allows the relay to reset itself once the thermal element has cooled sufficiently. Manual reset is the standard choice for most motor starter applications because it prevents automatic motor restart after a fault — a safety consideration in systems where unexpected motor restart could injure personnel or damage equipment. Automatic reset is appropriate only in unattended installations where remote restart is controlled through the control circuit and safety risks from automatic restart are addressed by other means.

Is the LRD350 a direct drop-in replacement for an older TeSys D thermal relay with screw clamp terminals?

Only if the older relay also had EVERLINK terminals — or if you are ordering the screw clamp variant specifically. EVERLINK and screw clamp versions of TeSys Deca relays are not directly interchangeable on the same contactor. Before ordering a replacement, confirm the terminal type on your existing installation. If the existing relay has screw clamp terminals, order the screw clamp version of the replacement relay. When in doubt, photograph the existing terminal area and share it with your distributor before the order is confirmed.

Can the LRD350 be used in a hazardous location or ATEX-rated enclosure?

The LRD350 carries ATEX 94/9/EC certification, which means it is approved for use in potentially explosive atmospheres when the installation meets the applicable ATEX zone requirements and the relay is installed within an appropriately rated enclosure. The relay's own IP20 rating means it is not directly exposed to the hazardous environment — it must be housed in a suitable enclosure. For applications where the relay itself serves as the primary protective device in a hazardous area, consult Schneider Electric's ATEX documentation and your applicable installation code to confirm the relay's suitability for the specific zone classification.

Why Order From LeadTime.ca

  • LeadTime.ca ships worldwide — the LRD350 and TeSys D accessories are available to buyers globally, not just in North America
  • Technical support before the order ships — confirm contactor compatibility, terminal type, and tripping class with a team that knows this product family
  • Sourcing for hard-to-find variants and urgent MRO replacements — specialist distributor inventory access reduces lead time risk on emergency orders
  • Volume pricing available for OEM builders and facility maintenance programs — contact for current pricing on multi-unit orders

LRD350 At-a-Glance Summary

  • Current setting range: 37 to 50 A, adjustable dial — motor nameplate FLA must fall within this window
  • Tripping class: Class 10A — trips within 10 seconds at 1.2x set current; not suitable for high-inrush compressor or crusher motors
  • Contact configuration: 1NO-1NC — verify your control circuit wiring before ordering
  • Terminal type: EVERLINK power terminals — confirm this matches your existing contactor; screw clamp variants exist and are not interchangeable
  • Compatible contactors: LC1D40A, LC1D50A, LC1D65A — not compatible with LC1D09 or TeSys K family
  • Enclosure rating: IP20 — requires installation inside a control panel or enclosure
  • Operating temperature: -20 to +60°C — verify ambient conditions at installation site
  • Standards: UL 508, CSA C22.2 No. 14, ATEX 94/9/EC, CE, RoHS, IEC 60947-4-1, IEC 60947-5-1
  • Motor protection capability: up to 22 kW at 400V with phase unbalance and stall detection per Schneider Electric published specifications
  • Warranty: 18 months from date of purchase
  • Availability: normally stocked in Schneider Electric distribution facilities; market-typical lead time 1 to 2 weeks — verify with distributor at time of order

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