Rotary Cam Switch (0-1 / 1-0-2) and Thermal Overload Relay (95-96 / 97-98) Wiring Guide
How to wire IEC 60947-3 0-1 isolator and 1-0-2 changeover cam switches, and connect IEC 60947-4-1 thermal overload relay 95-96 NC trip and 97-98 NO alarm contacts.
In industrial control panels, rotary cam switches (IEC / TS EN 60947-3) provide manual isolation and source changeover, while thermal overload relays (IEC / TS EN 60947-4-1) mount below a contactor to protect three-phase induction motors against sustained overload and phase-loss heating.
> Related Category: Compare technical specifications and model options directly in the Cam Switches, Thermal Overload Relays, and Contactors categories.
Rotary cam switch wiring (`0-1` vs `1-0-2` changeover)
| Switch Function | Positions | Wiring Principle | Engineering Rule |
|---|---|---|---|
| On–Off Isolator | `0 – 1` | Supply on `1-3-5`, load on `2-4-6` (plus 4th pole for neutral). | Size by AC-21A for resistive/mixed loads or AC-23A for direct motor switching. |
| Changeover Switch | `1 – 0 – 2` | Connect load to bridged common terminals, Source 1 (Mains) to group 1, and Source 2 (Generator) to group 2. | Center `0` dead-band prevents source paralleling; use 4-pole switches for mains-to-generator transfer. |
Thermal overload relay terminals (`95-96` NC & `97-98` NO)
A thermal overload relay does not break the three-phase power poles directly; instead, bimetal deflection opens its control contact in series with the contactor coil (see MPCB vs thermal overload relay):
- Power pins (`1/L1 - 3/L2 - 5/L3 → 2/T1 - 4/T2 - 6/T3`): Mount directly onto contactor load terminals; connect motor cable to `T1-T2-T3`.
- `95 – 96` (NC Trip Contact): Wire in series with the stop/start control circuit feeding contactor coil `A1`.
- `97 – 98` (NO Alarm Contact): Closes on overload trip to drive a panel fault lamp or PLC fault input.
- Current dial (Ir): Set to `1.0 × In` on direct-on-line starters, or `0.58 × In` when placed inside the delta winding loop of a star-delta starter.
Frequently asked questions
Does a thermal overload relay protect against short circuits?
No. Coordinate it with upstream back-up fuses or a magnetic motor protection circuit breaker per IEC 60947-4-1 Type 1 / Type 2 tables.
Should the reset selector be set to H (Manual) or A (Auto)?
Keep it on H (Manual) so a tripped motor cannot restart unexpectedly after the bimetals cool down.