Schneider TeSys LRD and LR9 Overload Relays: Full Range Review
What is the Schneider TeSys LRD and LR9 overload relay range? The TeSys LRD and LR9F bimetallic relays cover roughly 0.10 A to 630 A of motor full-load current under IEC 60947-4-1, clipping directly onto Schneider's TeSys D and TeSys F contactor frames, while the electronic LR9 (TeSys T) line does the same job over a wider 1:4 setting ratio with selectable trip class. Picking the wrong member of this range means either a relay that nuisance-trips on every start or one too coarse to protect the winding at all. This review covers the LRD bimetallic baseline, the LR9F extension for larger frames, the LR2K/LR3K line for small motors, the LR9 electronic option, how trip class and setting work across the family, and how each relay coordinates with its contactor.
LRD: The Bimetallic Baseline Under TeSys D
The TeSys LRD relay is the default overload relay for TeSys D (LC1D) contactors, the mainstay of Schneider's low-voltage motor starter line. It clips onto the base of the contactor without separate wiring for the main current path — the relay carries the same three phase conductors that feed the motor. Setting ranges start near 0.10 A for the smallest LRD models and step up through the family; each LRD variant covers a narrow current band, so the model number, not just the dial position, determines the usable range. Every LRD unit is Class 10A, temperature compensated, and phase-loss sensitive, with a selectable hand or auto reset and a STOP/TEST button on the front face.
What we see in the field: builders often grab whatever LRD is sitting in the parts bin rather than checking its current band against the motor nameplate. The dial numbers overlap between adjacent LRD models, so a relay set at the top of its range trips early and inconsistently compared with one sized so the FLC sits mid-scale.
LR9F: Bimetallic Coverage Above the LRD Range
Once a motor's FLC exceeds what an LRD frame handles — into the larger TeSys D and TeSys F contactor sizes — Schneider extends bimetallic protection with the LR9F family, reaching toward the 630 A ceiling of the combined LRD/LR9F range. Construction follows the same three-bimetal, differential-trip-bar principle as LRD: Class 10A, phase-loss sensitive, ambient compensated. Physical size grows with the current rating, and mounting shifts from direct clip-on to a busbar or cable-lug connection sized for the larger contactor frame.
LR2K and LR3K: TeSys K for Small and Fractional-Horsepower Motors
Below the LRD's lowest bracket, Schneider's TeSys K line (LR2K, LR3K) covers small and fractional-horsepower motors paired with the compact LC1K contactor. Function is unchanged from LRD — bimetallic, Class 10A, FLC-set dial — but frame and terminal sizing target motors where an LRD would be oversized for the enclosure. TeSys K suits control panels with tight DIN-rail budgets: small conveyor drives, dosing pumps, damper actuators.
LR9 (TeSys T): The Electronic Overload Relay
The LR9 line, marketed under TeSys T, replaces the bimetal element with current transformers feeding a microcontroller that models motor heating electronically. The setting ratio widens to roughly 1:4 against about 1:1.5 on a bimetal LRD, so one LR9 model spans a current range that would otherwise need several bimetal relays. Trip class is field-selectable rather than fixed, letting the same unit serve a Class 10 pump and a Class 30 crusher feeder by changing a parameter instead of swapping hardware. LR9/TeSys T also adds capability the bimetal line does not have: true phase-loss detection independent of the thermal element, phase-imbalance monitoring, stall and locked-rotor protection, and thermal memory that survives a power cycle so a motor stopped mid-heat-cycle does not restart as if it were cold.
The trade-off is cost and setup: LR9 needs the current range and class programmed rather than a single dial turn, and its diagnostics assume a control system that can read them out. For a single pump on a local start-stop station, that overhead buys little; for a motor control center with SCADA visibility, it is the reason to specify electronic in the first place.
Trip Class and Setting Across the Family
Every relay in the TeSys overload range — LR2K, LR3K, LRD, LR9F, and the default LR9/TeSys T configuration — ships or is set to Class 10A: a trip time of 2-10 s at 7.2x the current setting from a cold start, per IEC 60947-4-1. That covers standard pumps and fans whose run-up finishes in a few seconds. High-inertia loads need more: LR9/TeSys T can be reconfigured to Class 20 or Class 30, giving 6-20 s or 9-30 s at the same 7.2x test point, something the bimetal LRD/LR9F line cannot do because its curve is fixed by the bimetal geometry.
Formula: Trip Class Test Condition — Source: IEC 60947-4-1, Clause 7.2.1.2
ttrip measured at I = 7.2 × Iset, from cold
| Symbol | Description | Unit |
|---|---|---|
| Iset | Overload relay current setting (dial or programmed value, = motor FLC) | A |
| ttrip | Trip time at 7.2x setting, cold start (Class 10A: 2-10 s) | s |
Sizing itself does not change with trip class: the dial or programmed value is always the motor's nameplate FLC, adjusted for a star-delta sizing configuration where the relay sees line FLC divided by root three. Getting the class wrong shows up as nuisance tripping on every start; getting the setting wrong either lets the winding cook or trips a healthy motor. See how to select and set an overload relay for the FLC-to-dial procedure that applies to LRD, LR9F, and LR9 alike.
Coordination Type and Contactor Fit
Schneider publishes coordination tables pairing each TeSys overload relay with a specific TeSys D or TeSys F contactor and an upstream fuse or MPCB, declaring the achieved coordination type per IEC 60947-4-1. Type 2 coordination — no damage beyond light, separable contact welding after a short circuit within the declared rating — is the target for most industrial panels; Type 1 permits starter damage as long as no hazard to personnel results. Mixing an LRD or LR9F relay outside its published pairing with the contactor and SCPD voids the declared coordination type, even if the current ratings look compatible on paper. The same logic applies whether the starter uses a fuse or a motor protection circuit breaker ahead of the contactor; see Type 1 vs Type 2 coordination for how the classification is tested and declared.
LRD vs LR9F vs LR2K/LR3K vs LR9 (TeSys T): Range Comparison
| Criteria | LR2K / LR3K | LRD | LR9F | LR9 (TeSys T) |
|---|---|---|---|---|
| Type | Bimetallic | Bimetallic | Bimetallic | Electronic (CT-based) |
| Typical current coverage | Sub-fractional up to a few amps | ~0.10-100 A band | Extends toward 630 A | Wide programmable range |
| Setting ratio | ~1:1.5 | ~1:1.5 | ~1:1.5 | ~1:3 to 1:4 |
| Trip class | Fixed 10A | Fixed 10A | Fixed 10A | Selectable 10/20/30 |
| Extra protections | Phase-loss | Phase-loss | Phase-loss | Phase-loss, imbalance, stall, thermal memory |
| Contactor fit | LC1K | LC1D | Larger TeSys D / TeSys F | TeSys D / F frames, programmed |
The pattern holds across the thermal overload relay engineering guide's cross-brand comparison: a fixed-class bimetal line for the common case, an electronic line for the motors and loads that need more range or more diagnostics. This split is not unique to TeSys — see the IEC 60947-4-1 standards overview for how the same test conditions apply across every brand stocked in the thermal overload relays collection.
Frequently Asked Questions
What current range does the TeSys LRD overload relay cover?
Individual LRD models cover narrow bands starting near 0.10 A and stepping up through the family; combined with LR9F, the bimetallic TeSys line reaches roughly 630 A. Match the specific LRD model number to the motor's nameplate FLC rather than assuming one relay covers the whole range.
When should I use LR9 (TeSys T) instead of LRD?
Choose LR9 when the motor needs a trip class other than 10A, when the application needs stall, ground-fault-adjacent, or phase-imbalance protection beyond basic phase-loss, or when a control system needs to read diagnostics electronically. For a standard pump or fan on local control, LRD is simpler and needs no programming.
Are LRD and LR9F relays interchangeable with other Schneider contactor lines?
No. LRD and LR9F are sized and mechanically matched to TeSys D and TeSys F contactor frames; small TeSys K motors use LR2K/LR3K instead. Mixing frames outside Schneider's published pairings changes the mounting fit and can void the declared coordination type.
Does the LR9 electronic relay need external control power?
The current-sensing element is powered by the motor current itself for the core protection function, but the electronics and any communication or display features typically need a separate control voltage. Confirm supply requirements against the specific LR9/TeSys T model before wiring.
What trip class fits a high-inertia fan on a TeSys starter?
A Class 10A bimetal LRD or LR9F will likely nuisance-trip on a long run-up. Specify LR9 (TeSys T) set to Class 20 or 30 so the trip curve tolerates the longer starting current without giving up overload protection during a running fault.
Conclusion
The TeSys overload relay range splits along the same line as every major brand's: LR2K/LR3K and LRD/LR9F cover the bulk of motor starters with a fixed Class 10A bimetal element sized to the contactor frame, and LR9 (TeSys T) picks up the motors and loads that need a wider setting ratio, a different trip class, or protections beyond basic phase-loss. Sizing is the same exercise regardless of family: set the dial or program the value to the motor's nameplate FLC, respect Schneider's published coordination table for the contactor and upstream SCPD, and reach for LR9 only when LRD's fixed Class 10A genuinely does not fit the load.
