Schneider Electric LRD08 — Thermal Overload Relay Selection Guide

By Abdullah Zahid
16 min read
Schneider Electric LRD08 TeSys Deca thermal overload relay 2.5 to 4A Class 10A for LC1D contactor motor starter

Schneider Electric LRD08 TeSys Deca Thermal Overload Relay, 2.5 to 4 A, Class 10A — Specifications, Selection Guide, and Alternatives

If you are specifying motor overload protection for a small three-phase motor in the 1.1 to 1.5 kW range and your panel already runs TeSys contactors, the Schneider Electric LRD08 is almost certainly the relay on your shortlist. This TeSys Deca Thermal Overload Relay covers an adjustable 2.5 to 4 A thermal range, trips to Class 10A standards within 10 seconds at 130% of rated current, and includes built-in phase-loss sensitivity — all in a compact form that clips directly onto LC1D series contactors without additional hardware. The question is not whether the LRD08 is a capable device; it is whether your motor's full-load amperage and your contactor part number confirm it as the right one for your specific circuit.

If you have already confirmed the LRD08 is the correct part for your application, check current pricing and availability at LeadTime.ca — ships worldwide.

Who Should Buy the LRD08 — and Who Should Choose a Different Variant

The Schneider Electric LRD08 is the right relay for engineers and technicians whose motor FLA falls squarely in the 2.5 to 4 A range and whose panel uses TeSys LC1D contactors. Check all of the following before ordering:

  • Motor nameplate full-load amperage (FLA or In) falls between 2.5 A and 4 A
  • Trip speed requirement is Class 10A — relay trips within 10 seconds at 130% of rated current
  • Contactor part number is one of: LC1D09, LC1D12, LC1D18, LC1D25, LC1D32, or LC1D38
  • Supply is three-phase AC — the LRD08 is a three-pole relay; single-phase and DC-primary circuits are not the intended application
  • Screw clamp terminals are acceptable — the LRD08 uses screw clamp on both power and control circuits; spring or EverLink terminal variants exist across the TeSys range if required
  • Installation environment falls within -20 to +60°C ambient — thermal calibration drifts outside this range

If your motor FLA is 4 to 6 A, the LRD10 is the correct choice. If FLA runs 6 to 10 A, specify the LRD16. For motors above 10 A, the TeSys LRD family extends upward to the LRD140 — consult the family datasheet for the exact model.

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What the LRD08 Actually Does in a Motor Starter Circuit

The Schneider Electric LRD08 is a differential thermal overload relay — a passive protection device that sits between the contactor and the motor, continuously monitoring current on all three power phases. Its bimetallic thermal element responds to current-induced heat: when sustained overcurrent pushes the element beyond the calibrated threshold, the relay trips its internal latch, opening the normally-closed control circuit contact and signaling the contactor to drop out and remove power from the motor.

What distinguishes the LRD08 from simpler overload devices is its three-pole differential design. By monitoring all three phases simultaneously, it detects not only sustained overcurrent but also phase-loss events — single-phase failure and phase imbalance conditions. Per the verified specification, the relay trips at 130% of rated current on two phases when the third phase reads zero. This means a single LRD08 replaces what would otherwise require both a thermal overload relay and a separate phase-failure monitor, reducing component count and panel wiring complexity.

The reset mode is field-selectable without any component swap. The blue push-button on the relay face rotates to switch between manual reset — where an operator must physically press the button after a trip, the safer choice for unattended equipment — and automatic reset, where the relay self-resets once the overload condition clears. The red push-button provides a stop function for control circuit use. Both modes are suitable for industrial applications; the correct choice depends on whether the equipment operates attended or unattended and what the machine safety design document specifies for restart behavior after a fault.

Typical System Architecture: Where the LRD08 Sits in the Signal Chain

The LRD08 occupies the motor protection layer of the starter assembly, positioned between the switching contactor and the motor terminal box. Understanding this placement helps commissioning engineers visualize what happens upstream and downstream when the relay trips.

  • Three-phase AC supply enters through an upstream circuit breaker or fuse disconnect, providing short-circuit protection that the LRD08 does not supply
  • The LC1D series contactor (LC1D09 through LC1D38) sits upstream of the LRD08, switching the motor on and off under control circuit command
  • The LRD08 clips directly onto the contactor's downstream face or mounts standalone on DIN rail, passing all three motor phases through its thermal elements at 1.7 N.m screw clamp terminals accepting 1.0 to 2.5 mm² flexible cable
  • Motor cable exits the LRD08 output terminals and connects to the motor terminal box — the relay monitors real-time current on this segment continuously while the motor runs
  • The LRD08 auxiliary contacts (1NO-1NC, rated 10 A control circuit) connect into the PLC or control panel logic, signaling a fault condition or enabling alarm output when the relay trips

Typical Applications and Deployment Scenarios

The LRD08 finds its home in any application running small three-phase AC motors in the 1.1 to 1.5 kW range at 400 V. In food and beverage processing, it protects conveyor motors, mixer drives, and small pump motors where consistent uptime and phase-loss detection are both required — a single winding failure from undetected phase loss can destroy a motor in minutes. In packaging machinery, where OEMs assemble compact TeSys starter kits at volume, the LRD08 is a standard kit component that ships pre-specified by the machine builder.

HVAC applications — small fan motors, chilled water pump drives, cooling tower fans — benefit from the automatic reset mode option, allowing the relay to self-recover from brief thermal events without requiring a maintenance call. Material handling systems, including hoists, conveyors, and transfer carriages driven by sub-2 kW motors, use the LRD08 as the default overload element in their motor control centers.

Retrofit and modernization projects represent another strong use case. When an aging thermal overload relay fails in a panel already running LC1D contactors, the LRD08 drops in directly with no contactor replacement required, provided the contactor part number falls within the LC1D09-to-LC1D38 compatibility range. For system integrators maintaining a standard small-motor-protection bundle, the LRD08 is a logical stock item alongside a matched LC1D contactor.

Application Typical Deployment
Food and beverage processing Conveyor motor starter, mixer drive protection, small pump control — TeSys contactor and LRD08 as compact assembly
Packaging machinery OEM Pre-assembled motor starter kit for 1.1-1.5 kW drives; LRD08 specified as standard SKU in machine BOM
HVAC fan and pump drives Automatic reset mode configured; relay self-recovers from brief thermal events; mounted on LC1D contactor in MCC
Material handling (conveyors, hoists) Manual reset mode for safety; operator intervention required after overload trip; contactor-mounted in control cabinet
Control panel retrofit Drop-in replacement for failed thermal relay in existing LC1D-based starter; no rewiring of power circuit required
System integrator standard kit Pre-stocked as part of 2.5-4 A motor protection bundle; combined with LC1D09 or LC1D12 for small-motor applications

LRD08 Specifications Engineers Need at the Point of Purchase

Specification Value
Thermal Range 2.5 to 4 A (adjustable)
Trip Class Class 10A — trips within 10 seconds at 130% rated current (IEC 60947-4-1)
Contact Form 1NO-1NC; 10 A control circuit rating
Power Circuit Voltage 690 V AC (IEC); 600 V AC/DC (UL/CSA)
Phase-Loss Sensitivity Yes — trips at 130% of Ir on two phases with third phase at zero
Reset Mode Manual or Automatic (field-selectable via blue push-button)
Ambient Temperature Range -20 to +60°C
Protection Degree IP20 (IEC 60529)
Contactor Compatibility LC1D09, LC1D12, LC1D18, LC1D25, LC1D32, LC1D38 (contactor-mounted or standalone)
Standards Compliance RoHS, CE, ATEX 94/9, UL 508, CSA C22 2 No. 14, IEC/EN 60947-4-1, IEC/EN 60947-5-1

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

LRD08 vs LRD10 vs LRD16: Which Thermal Overload Relay Do You Actually Need?

Feature LRD08 LRD10 LRD16
Thermal Range 2.5–4 A 4–6 A 6–10 A
Motor Size (typical, 400 V 3-phase) 1.1–1.5 kW 1.5–2.2 kW 2.2–3.7 kW
Trip Class 10A 10A or 20A 10A or 20A
Mount Type Contactor or Standalone Contactor or Standalone Contactor or Standalone
Form Factor Same Same Same
Phase-Loss Detection Yes Yes Yes
Reset Modes Manual / Automatic Manual / Automatic Manual / Automatic
Pricing Available on product page Contact for current pricing Contact for current pricing

All three models share the same TeSys mounting platform, identical terminal types, and the same LC1D contactor compatibility range — making it straightforward to standardize on one product family across a range of motor sizes. The decision point is purely the motor nameplate FLA. If your motor FLA is at or above 4 A, the LRD08 is not the right relay — check current availability of the LRD10 and LRD16 at LeadTime.ca.

Expert Verdict: Is the LRD08 Right for Your Application?

The Schneider Electric LRD08 earns its place as a standard-stock item for a specific and well-defined buyer profile: plant engineers and maintenance supervisors running TeSys infrastructure who need reliable, no-surprises overload protection for motors in the 1.1 to 1.5 kW range. Its Class 10A trip performance — verified against IEC 60947-4-1 — combined with built-in phase-loss sensitivity means one device handles what would otherwise require two separate relays in the control circuit. For system integrators pre-assembling motor starter kits, for OEM machine builders specifying CSA- and UL-compliant protection for North American deployments, and for retrofit technicians swapping out a failed relay in an LC1D-based panel, the LRD08 is a clean, low-risk specification choice. The field-selectable reset mode and screw clamp terminals keep commissioning straightforward and troubleshooting accessible to any technician familiar with TeSys hardware.

The LRD08 has real limits that honest specification requires acknowledging. It is a three-phase AC device — single-phase motor circuits and primary DC applications fall outside its design envelope. The IP20 protection rating rules it out for washdown environments and areas classified under ATEX for explosive atmospheres without supplementary enclosure engineering. Most critically, the 4 A upper boundary of its thermal range is a hard constraint: if your motor FLA is 4 to 6 A, the LRD10 is the correct part; for 6 to 10 A, specify the LRD16. Class 20 trip speed variants exist across the TeSys LRD family for high-inrush or frequent-start applications where Class 10 trips too quickly during normal motor starting — the LRD08 itself is Class 10A only. Equipment operating continuously outside the -20 to +60°C ambient range will experience thermal calibration drift and should be assessed against a variant with extended temperature tolerance.

From a procurement standpoint, the LRD08 is a commodity-class item with no chronic backorder risk — it stocks consistently at major authorized industrial distributors and typically ships within one to three business days from order. That said, sourcing through a specialist industrial distributor rather than a generic channel matters more than it might appear for this type of component: the risk of ordering the wrong current range is high among buyers who skip the motor nameplate verification step, and a specialist distributor will catch that mismatch before the order ships rather than after a return is initiated. For volume orders, blanket pricing, or urgent replacement scenarios, check current availability and pricing for the LRD08 at LeadTime.ca — we ship worldwide.

For volume pricing or to confirm lead time before committing to a build, contact the LeadTime.ca team directly — we ship worldwide.

What Engineers Need to Know Before Ordering the LRD08

Community forum data for this specific model was not available at the time of publication — the LRD08 is a mature, well-understood commodity device and much of the practical knowledge around it lives in distributor application notes and plant engineering documentation rather than active online discussion threads. What that means for a buyer in specification mode is that the failure points are well-catalogued from field experience, and the ordering mistakes are predictable. The wrong-part risks here are not obscure edge cases; they are the same selection errors that occur across any thermal overload relay family, and they are entirely avoidable with a disciplined pre-order checklist.

The single most common ordering mistake is specifying the LRD08 for a motor whose FLA exceeds 4 A. This happens when a buyer orders by memory from a previous project without re-checking the motor nameplate on the current machine, or when a procurement team substitutes part numbers based on physical similarity rather than current range. An LRD08 on a motor whose FLA is, say, 5 A will trip repeatedly during normal operation — not because the motor is overloaded, but because the relay's thermal element is already being pushed beyond its calibrated range at rated motor current. The consequence is nuisance trips, unnecessary downtime, and eventually a frustrated technician increasing the setpoint dial past the safe threshold to stop the trips — at which point the motor loses effective overload protection entirely.

The second common mistake involves reset mode. The LRD08 ships with a field-selectable reset mode, but buyers who do not explicitly configure this before installation may leave equipment in automatic reset mode when manual was required by the machine safety design. For unattended equipment, automatic reset after an overload trip creates a restart hazard — the motor restarts without operator awareness once the thermal condition clears. Consult the machine FMEA or safety design document before commissioning and document the selected mode on the control panel nameplate. When community feedback is sparse for a device like this, the distributor's applications team becomes the most reliable pre-order resource: before ordering, confirm your motor FLA, your contactor part number, and your required reset mode with a distributor who knows the TeSys product line. LeadTime.ca provides exactly that level of pre-order technical support — contact us before placing your order if any of these parameters are uncertain.

Wiring and Installation Overview

The following is an overview of the key installation requirements for the LRD08. For full wiring diagrams and step-by-step procedures, refer to the Schneider Electric installation manual for the TeSys LRD series.

  • Power circuit terminals (L1, L2, L3) accept 1.0 to 2.5 mm² flexible copper cable; tighten all screw clamp terminals to 1.7 N.m — use a torque wrench or calibrated screwdriver, not hand-tight estimation; crimp ferrules on cable ends are strongly recommended to prevent strand splaying under clamp pressure
  • For contactor-mounted configuration, align the LRD08 with the LC1D contactor mounting clips and press firmly until the relay seats flush — no additional fixation hardware is required; verify the contactor part number is within the LC1D09–LC1D38 compatibility range before mounting
  • For standalone mounting, the LRD08 mounts to standard DIN rail; confirm 70 mm depth clearance and 45 mm width allocation in the enclosure before positioning
  • Select reset mode before applying power: rotate the blue push-button to manual (operator must physically reset after trip) or automatic (relay self-resets when overload clears); document the selected mode on the panel nameplate
  • Set the thermal adjustment dial to 1.0 to 1.2 times motor FLA before commissioning; verify all three phases are present at relay input terminals using a multimeter on AC scale before energizing the circuit

Compatible System Components and Expansion

The LRD08 is designed to integrate directly within the TeSys D and TeSys Deca motor starter ecosystem. The following components are compatible with the LRD08 in typical motor starter assemblies:

  • LC1D09 — TeSys D contactor, 9 A; smallest contactor in the compatible range, commonly paired with LRD08 for 1.1 kW motors
  • LC1D12 — TeSys D contactor, 12 A; suitable pairing for 1.1–1.5 kW motor starters with LRD08
  • LC1D18 — TeSys D contactor, 18 A; used when the full starter assembly must accommodate larger short-circuit withstand while LRD08 handles overload protection for motors at the lower end of the contactor's range
  • LC1D25 — TeSys D contactor, 25 A; compatible with LRD08 in applications where the contactor is sized for future motor upgrades but current motor FLA remains within 2.5–4 A
  • LC1D32 — TeSys D contactor, 32 A; direct mounting confirmed; LRD08 clips to this contactor without additional hardware
  • LC1D38 — TeSys D contactor, 38 A; the largest contactor in the LRD08 compatibility range; verify enclosure terminal clearance for this assembly size

Wrong-Part Prevention Checklist

Before placing your order for the LRD08, work through every item on this checklist. Each point corresponds to a confirmed ordering risk for this model:

  1. Verify motor full-load amperage (FLA) from motor nameplate falls within 2.5-4A range; if motor FLA exceeds 4A, do NOT order LRD08 — order LRD10 or higher
  2. Confirm contactor part number is LC1D09, LC1D12, LC1D18, LC1D25, LC1D32, or LC1D38 — LRD08 fits these exclusively
  3. Check whether standalone mounting or contactor-mounted configuration is required; LRD08 supports both but verify terminal clearance in enclosure
  4. Confirm reset mode needed: manual (default; operator must physically reset after trip) or automatic (relay resets when fault clears) — set before installation
  5. Verify three-phase AC supply; LRD08 is rated for AC networks only, not DC
  6. Check ambient temperature in installation location falls within -20 to +60°C; outside this range, thermal calibration drifts
  7. Confirm no external phase-failure relay is already in circuit; LRD08 includes phase-loss detection — dual protection is redundant cost
  8. Verify supply frequency is 0-400 Hz (standard industrial); some industrial sites operate at non-standard frequencies where this relay may not function correctly

If any item on this checklist raises a question before your order is placed, review the full product details at LeadTime.ca or contact our team for application support — we ship worldwide and can help confirm compatibility before you commit.

Frequently Asked Questions

Can the LRD08 protect a single-phase motor?

No. The LRD08 is a three-pole relay that monitors all three phases simultaneously. Its phase-loss detection function depends on monitoring the differential current across all three poles. Single-phase motor circuits require a different device — the LRD08 is not rated or configured for single-phase protection.

Does the LRD08 include short-circuit protection, or do I still need a separate circuit breaker?

The LRD08 is a thermal overload relay only — it protects against sustained overcurrent and phase-loss conditions but does not interrupt the main power circuit on a short-circuit fault. A separate upstream circuit breaker or fuse disconnect is required for short-circuit protection. The LRD08 auxiliary contacts signal the contactor to drop out on an overload trip; the contactor, not the LRD08, removes power from the motor.

Is the LRD08 a direct drop-in replacement for an older TeSys thermal relay in an existing LC1D panel?

Yes, provided the existing contactor is within the LC1D09 to LC1D38 range and the motor FLA falls within 2.5 to 4 A. The LRD08 uses screw clamp terminals accepting 1.0 to 2.5 mm² flexible cable — verify that the existing cable gauge matches before installing. If the contactor is from a different TeSys series (TeSys U, TeSys F, or older Square D series), consult the compatibility chart or contact your distributor before ordering.

What does the built-in phase-loss detection actually do, and does it eliminate the need for a separate phase monitor relay?

The LRD08 monitors current on all three phases and trips at 130% of rated current on two phases when the third phase reads zero — this covers single-phase loss and significant phase imbalance. In most small motor applications, this built-in sensitivity is sufficient and eliminates the need for a separate phase-failure monitor relay. If your application requires phase sequence detection or tighter phase imbalance thresholds, verify whether the LRD08's sensitivity specification meets that requirement before removing a dedicated phase monitor from the circuit.

How do I confirm the thermal setpoint is correct after installation?

Set the adjustment dial to 1.0 to 1.2 times motor FLA before energizing. During commissioning, measure actual motor running current with a clamp meter under rated load and compare to the dial position — adjust if necessary. After commissioning, simulate an overload condition to verify the relay trips within 10 seconds at 130% of the setpoint, confirming Class 10A performance. Document the final setpoint value on the motor starter nameplate for future reference.

What is the consequence of setting the thermal dial too high to stop nuisance trips?

Setting the thermal setpoint above 1.2 times motor FLA reduces the relay's ability to protect the motor winding from genuine overload conditions. At an excessively high setpoint, the motor can run beyond its thermal limit without triggering a trip — leading to insulation breakdown, winding damage, and potentially motor failure or fire. If nuisance trips persist after correct setpoint adjustment, the cause is likely a motor FLA that exceeds the LRD08's 4 A upper limit, in which case the correct resolution is to order the LRD10 or appropriate higher-range variant, not to increase the dial past the motor's rated current.

Why Order From LeadTime.ca

  • Ships worldwide — no geographic restriction on orders; international procurement is straightforward
  • Application support available before you order — confirm motor FLA compatibility, contactor part number, and terminal type with a team that knows the TeSys product line
  • Specialist industrial distributor — not a generic marketplace; wrong-part selection risk is identified and flagged before shipment, not after a return
  • Volume pricing available — contact for blanket order pricing on multi-unit requirements across the TeSys LRD family
  • Fast response on availability and lead time — standard stock item with typically same-day to three-business-day lead time

At-a-Glance Summary

  • Model: Schneider Electric LRD08 — TeSys Deca Thermal Overload Relay, 2.5 to 4 A, Class 10A
  • Thermal range: 2.5 to 4 A adjustable; Class 10A trip within 10 seconds at 130% of rated current per IEC 60947-4-1
  • Typical motor protection range: 1.1 to 1.5 kW at 400 V three-phase
  • Contact form: 1NO-1NC auxiliary contacts; 10 A control circuit rating
  • Power circuit voltage: 690 V AC (IEC); 600 V AC/DC (UL/CSA)
  • Phase-loss sensitivity: Yes — trips at 130% of Ir on two phases with third phase at zero; no separate phase monitor relay required
  • Reset mode: Manual or Automatic — field-selectable via blue push-button rotation, no component swap required
  • Contactor compatibility: LC1D09, LC1D12, LC1D18, LC1D25, LC1D32, LC1D38 — direct contactor-mounted clip or standalone DIN-rail mounting
  • Terminal type: Screw clamp, 1.0 to 2.5 mm² flexible cable, 1.7 N.m torque
  • Dimensions: 70 mm depth x 45 mm width x 66 mm height; weight 0.124 kg
  • Ambient temperature: -20 to +60°C; IP20 protection rating
  • Standards: RoHS, CE, ATEX 94/9, UL 508, CSA C22 2 No. 14, IEC/EN 60947-4-1, IEC/EN 60947-5-1
  • If motor FLA exceeds 4 A: order LRD10 (4–6 A) or LRD16 (6–10 A) — same form factor, same mounting platform

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