Manual vs Automatic Reset on Overload Relays: Which to Use
Manual or automatic reset on an overload relay? The reset mode set on a thermal overload relay (bimetallic or electronic, per IEC 60947-4-1) decides whether the 95-96 auxiliary contact re-closes on its own once the bimetal cools below the trip point, or stays open until a technician presses the reset button and confirms the fault is cleared. Pick automatic on the wrong motor and a stalled pump or jammed conveyor can restart itself into the same fault with nobody aware it ever tripped; pick manual where automatic was intended and a process sits idle for hours waiting on an operator who never got an alarm. This article covers how the two mechanisms differ internally, the 95-96/97-98 contact pair behind them, why HAND reset is the default on most motors, when AUTO reset is safe to use, and how trip class affects the cool-down time before reset.
How Manual (Hand) Reset Works
On a bimetallic relay, the trip bar releases a latch when the bent bimetal strips cross the set point. In HAND mode that latch stays mechanically tripped after the strips cool back to shape — the 95-96 contact stays open and the 97-98 contact stays closed until someone pushes the reset button on the relay face. The button only re-engages the latch; it does nothing to the bimetal itself. Push it before the strips have cooled and most relays simply refuse to reset, which is a built-in interlock, not a defect.
Electronic overload relays reproduce the same behavior in firmware. A microcontroller models the winding temperature from measured current, flags a fault when the modeled value crosses the threshold, and holds the output relay open until a reset input is pulled low — by a physical button, a remote contact, or a fieldbus command, depending on the model.
How Automatic Reset Works
Flip the selector to AUTO and the latch is bypassed. Once the bimetal strips cool past the reset threshold — typically a couple of minutes after a trip, longer for a relay set near the top of its range — the 95-96 contact closes again on its own. If the contactor coil circuit is still live at the control switch or the PLC output, the motor restarts without anyone touching anything. That is the entire point of the mode, and also its entire risk: the relay does not know why the motor overloaded, only that the strips are now cool enough to permit another try.
Why Manual Reset Is the Default for Most Motors
A tripped overload almost always means something is wrong upstream of the relay: a jammed mechanism, a seized bearing, a blocked pump impeller, a phase gone missing at a terminal. None of those clear themselves in the two or three minutes it takes a bimetal to cool. HAND reset forces a person to look at the machine, find the cause, and only then push the button — which is exactly the checkpoint you want on anything with moving parts near people, anything expensive to damage on a repeat fault, or anything where a surprise restart is a safety hazard.
What we see in the field: panel builders who default every relay to AUTO to save nuisance callbacks end up with the opposite problem — a conveyor that restarts itself three times before someone notices the motor is drawing 130% of FLC on a worn bearing, by which point the winding insulation has taken real damage. HAND reset would have stopped that on trip one.
When Automatic Reset Is Safe to Use
AUTO reset earns its place on equipment where an unattended restart genuinely does no harm — some sump and drainage pumps, well pumps, and float-switch-controlled loads where the trip is more likely a nuisance (short-cycling on start, a momentary overload) than a mechanical fault, and where restarting unattended is the entire purpose of the control scheme. It also shows up on unmanned or remote sites where a technician cannot reach the panel quickly and the cost of a stalled pump (a flooded pit, for instance) outweighs the cost of a motor restarting into a transient fault it may clear on its own.
This depends on how the rest of the control circuit is built, not just the relay: an AUTO-reset overload wired into a start/stop circuit with a sealed-in auxiliary contact will not restart on its own even after the relay resets, because the seal-in contact opened when the coil dropped out. Wire it into a maintained (level- or float-switch) circuit instead, and the motor comes back the moment the relay allows it.
Reset Mode, Trip Class, and Cool-Down Time
Trip class and reset mode interact through one shared variable: how much heat the bimetal (or the modeled winding, on an electronic relay) absorbed before it tripped. A Class 30 relay tolerates a 9-30 s run-up at 7.2x the setting before tripping, which means it has stored roughly three times the thermal energy of a Class 10A relay tripping in 2-10 s at the same current. That energy has to dissipate before the strips (or the model) drop back below the reset threshold, so a higher trip class generally means a longer wait before an AUTO-reset relay re-closes, and a longer minimum wait manufacturers specify before a HAND reset attempt will succeed.
Formula: Trip time at 7.2x setting — Source: IEC 60947-4-1, trip class table
ttrip = f(Class), tested at I = 7.2 × Iset from cold
| Symbol | Description | Unit |
|---|---|---|
| t_trip | Maximum trip time at 7.2x the current setting, tested cold | s |
| I_set | Current dial setting (should equal motor FLC) | A |
| Class | 10A: 2-10 s, 10: 4-10 s, 20: 6-20 s, 30: 9-30 s | - |
The practical consequence: on a high-inertia load running Class 20 or Class 30 to survive a long run-up, do not expect an AUTO-reset relay to re-close within the same minute or two you would see on a Class 10 pump trip. Check the manufacturer's cool-down spec before assuming a fixed reset delay across the whole product line.
Wiring the Reset Selector and the 95-96 / 97-98 Contacts
Every general-purpose overload relay ships with one NC contact pair (95-96) wired in series with the contactor coil, and one NO contact pair (97-98) usually taken to a PLC input or an indicator lamp for remote fault signaling. The 95-96 contact is what actually stops the motor — open it, and the coil drops out regardless of reset mode. The reset selector (HAND/AUTO) and the STOP/TEST button are separate from this contact pair; TEST simulates a trip mechanically for commissioning checks, and STOP breaks the coil circuit directly as a local E-stop on some relay models.
During commissioning, verify the reset mode with the TEST button before the motor ever runs: push TEST, confirm the contactor drops out, and confirm it either stays out (HAND) or re-closes after the expected delay (AUTO) once TEST is released. A selector left in the wrong position is invisible until the first real overload, by which point it is a production problem, not a commissioning one.
Manual vs Automatic Reset Across Schneider, ABB, and Siemens
Schneider's TeSys LRD bimetallic relays and the larger LR9F frames carry a HAND/AUTO selector on the front face alongside the FLC dial, with the STOP/TEST button built into the same housing that clips under an LC1D contactor. ABB's TA line (TA25DU through TA200DU and up) and the TF42 for compact AF contactors follow the same layout — selector, dial, and test button on one face, temperature compensated and phase-loss sensitive regardless of which reset mode is selected. Siemens SIRIUS 3RU21 relays mount the same HAND/AUTO switch on the frame-size-specific body (S00 through S3) that snaps onto a 3RT2 contactor. On all three brands, the electronic lines (Schneider LR9/TeSys T, ABB's E-series, Siemens 3RB30/3RB31) add the same selector plus, on some models, a remote reset input for PLC-driven acknowledgment instead of a physical button.
| Criteria | Manual (Hand) Reset | Automatic Reset |
|---|---|---|
| Restart after trip | Requires a deliberate button press or remote reset signal | Re-closes on its own once the thermal element cools |
| Default use case | Most motors: pumps, fans, conveyors, compressors near personnel | Unattended pumps and float-controlled loads where restart is intended |
| Fault diagnosis | Forces inspection before restart | No forced inspection — cause may go unnoticed |
| Wiring dependency | Works as-is in a sealed-in start/stop circuit | Only auto-restarts if the control circuit is a maintained (not sealed-in) type |
| Available on | Schneider TeSys LRD, ABB TA/TF, Siemens SIRIUS 3RU21 (selector switch) | Same relays, same selector, opposite position |
Frequently Asked Questions
What do the 95-96 and 97-98 contacts on an overload relay mean?
95-96 is the normally-closed contact pair wired in series with the contactor coil; it opens on a trip and stops the motor regardless of reset mode. 97-98 is the normally-open pair, typically wired to a PLC input or a fault lamp for remote signaling.
Can I switch an overload relay from manual to automatic reset in the field?
On most bimetallic and electronic relays, yes — a HAND/AUTO selector switch on the relay face changes the mode without rewiring. Confirm the change with a TEST button trip before returning the motor to service, since the control circuit wiring (sealed-in vs. maintained) also has to support the intended restart behavior.
How long does an automatic reset relay wait before re-closing after a trip?
Typically a couple of minutes on a Class 10 relay tripped near its setting, longer on a higher trip class or a relay that tripped deep into overload, because more stored heat has to dissipate. Manufacturers publish a minimum reset time in the relay's technical data; treat it as a floor, not a guarantee.
Does phase-loss protection reset the same way as a standard thermal trip?
Yes — a phase-loss trip releases the same trip bar (bimetallic) or the same output relay (electronic) as an ordinary overload, so it follows whatever reset mode the selector is set to. The relay does not distinguish the reset behavior by fault type, only by cooling state.
Is automatic reset allowed on all motors by code?
IEC 60947-4-1 permits both modes and leaves the choice to the application; it does not mandate HAND reset. The practical constraint is safety, not code compliance — an unattended restart must not endanger persons or equipment, which is why most specifications default to HAND unless the application specifically calls for AUTO.
Conclusion
Reset mode is a small selector switch with an outsized consequence: it decides whether a tripped motor waits for a person or tries again on its own. Default to HAND reset, verify it with the TEST button at commissioning, and reserve AUTO for the specific, documented cases — mainly unattended pumps on maintained control circuits — where an unwitnessed restart is genuinely the intended behavior rather than an oversight. For the setting that has to be correct before any of this matters, see how to select and set a thermal overload relay for a motor; for the trip-time behavior that governs how long a relay stays tripped before either reset mode can act, see overload relay trip classes 10A, 10, 20 and 30. Phase-loss faults follow the same reset logic covered in phase-loss and single-phasing protection, and the full mechanism sits within the broader thermal overload relay engineering guide. Schneider TeSys, ABB TA, and Siemens SIRIUS relays covering both reset modes are available in the thermal overload relays collection, alongside the contactors they mount under.
