Star-Delta (0-Y-Δ) and Reversing (1-0-2) Cam Switch Motor Wiring Diagram
IEC 60947-3 manual star-delta cam switch wiring with 6-lead motor terminal blocks (U1-V1-W1 / W2-U2-V2), 400/690 V nameplate verification, and 1-0-2 reversing vs changeover switches.
Star-delta (`0-Y-Δ`) and reversing (`1-0-2`) rotary cam switch wiring provides manual IEC 60947-3 motor starting, rotation reversal, and dual-source transfer for three-phase induction motors and distribution panels. Before terminating conductors, always verify the motor's voltage nameplate against mains line voltage and check whether the brass terminal links inside the motor box must be removed.
> Related Category: Browse current ratings and pole layouts in Star-Delta Switches, Pole-Changing Reversing Switches, and Cam Switches.
1. Motor nameplate rule for 400 V star-delta starting (`400/690 V`)
On a standard `3×400 V AC` industrial supply, each stator winding receives full `400 V` line-to-line voltage once switched into delta (`Δ`):
| Motor nameplate | Continuous connection on 400 V mains | Suitable for `0-Y-Δ` starting? | Engineering reason |
|---|---|---|---|
| 230 / 400 V (Δ / Y) | Star (Y) only | No (Winding burnout) | Windings are rated for 230 V; switching to Δ applies 400 V across 230 V coils |
| 400 / 690 V (Δ / Y) | Delta (Δ) | Yes (Compatible) | In Y start each coil gets `400 / √3 = 230 V`, reducing starting current & torque to 1/3 (33%) |
Because starting torque drops to one-third of direct-on-line (DOL) torque, star-delta starting is suited to low-inertia or unloaded starts such as centrifugal pumps, fans, and unloaded air compressors.
2. 6-wire `0-Y-Δ` cam switch and motor terminal box wiring
When wiring manual star-delta switches, remove all three brass jumper bars inside the motor terminal box and run 6 individual phase conductors (`U1, V1, W1` and `W2, U2, V2`) from the cam switch to the motor:
- Supply input (`L1, L2, L3`): Feed from an upstream motor protection circuit breaker into the cam switch line terminals.
- Winding starts (`U1, V1, W1`) & winding ends (`W2, U2, V2`): Match each terminal strictly to the switch manufacturer's contact chart so phase pairing (`U1-W2`, `V1-U2`, `W1-V2`) is preserved in delta.
- Operating sequence:
- `0` (Off): All supply poles isolated.
- `Y` (Star): Internal cams bridge `W2-U2-V2` while energizing `U1-V1-W1`. Hold in `Y` for 3–8 seconds until rotor speed reaches 75–85% of rated RPM.
- `Δ` (Delta): The star bridge opens and windings connect across `400 V` line-to-line for continuous full-torque operation. For automated contactor panels with a fixed `50 ms` transition pause, pair contactors with star-delta timer relays.
3. `1-0-2` reversing vs mains-generator changeover cam switches
Pole-changing reversing switches serve two distinct circuit topologies:
- 3P motor forward–off–reverse (`1-0-2` Reversing): Keep the star or delta brass links installed inside the motor box and run 3 phase wires plus PE. Position `1` passes `L1-L2-L3`; position `2` swaps two phases (`L1` and `L2`) via internal jumpers to reverse stator field rotation. Always wait at `0` until the shaft comes to a complete stop before switching to reverse to avoid severe plugging current.
- 4P mains–off–generator changeover (`1-0-2` Transfer): Connects two separate sources (`1 = Grid`, `0 = Off`, `2 = Generator/UPS`) to one load bus. Always select a 4-pole (`3P+N`) switch so the neutral conductor transfers cleanly without ground loops or nuisance RCD tripping.
For AC-3 vs AC-1 current sizing and overload protection, see Rotary Cam Switch and Thermal Overload Relay Wiring.
Frequently asked questions
Can a 230/400 V motor be started star-delta on a 400 V supply?
No. A 230/400 V motor is insulated for 230 V per winding and must remain permanently star-connected on 400 V mains. Only 400/690 V (or 380/660 V) motors can run continuously in delta on 400 V.
What happens if the brass links are left on the motor terminals with a star-delta switch?
Leaving star or delta links bolted across U2-V2-W2 or U1-W2 creates a direct phase-to-phase short circuit as soon as the cam switch transitions, immediately tripping the upstream breaker.
Why must 4-pole changeover switches be used for generator transfer?
Grid and generator neutrals often have separate earthing references; switching all 3 phases plus neutral (`4P`) prevents neutral backfeed, circulating earth currents, and nuisance 30 mA / 300 mA RCD trips.
How long should the operator stay in the Star (Y) position?
Stay in Star only until the motor accelerates to roughly 80% of rated speed (typically 3 to 7 seconds), then switch briskly into Delta. Running a loaded motor continuously in Star causes stalling and rapid thermal overload.