The motor nameplate decides it. Match the inverter to the motor’s phase and voltage, and the choice is made for you: single-phase for small pumps, three-phase for larger ones, with 380V three-phase the standard step for bigger farm and deep-well systems.
What Single-Phase and Three-Phase Mean
Single-phase power has one live conductor and suits small motors; three-phase power has three, and suits larger motors that start smoother and run more evenly under load. The inverter must output the same phase and voltage the motor is built for.
Why the Wrong Phase Is Not a Small Mistake
The wrong phase is not a small mistake: a three-phase motor will not run properly from a single-phase inverter, and a single-phase motor must not be fed three-phase power. The 380V article shows a three-phase system working end to end, from panels through the inverter to the pump.
When to Decide
Decide from the motor nameplate at design time, before the inverter is ordered. Revisit it when a pump is replaced with a larger one, or when a deep well is drilled and the pump step grows.
Where Each Phase Fits
Home gardens and small holdings usually run single-phase; larger farms and deep wells run 380V three-phase, where the QB100-PV 400V three-phase models’ DC 250-900V MPPT window applies, as the 380V article sets out.
How to Choose the Right Phase
- Read the motor nameplate: voltage and phase first, power second.
- Match the inverter output to the nameplate exactly: same phase, same voltage.
- Convert HP to kW with the HP-to-kW article’s chart before comparing ratings, so the comparison uses one unit.
- Size the inverter one rating step above the motor, as the sizing article advises, and check the MPPT window against the string voltage.
- For deep settings, check the pump setting depth and cable run with the deep-well article’s pre-purchase checklist.
- Confirm dry-run protection and level sensors are fitted before the first start, as the first start-up checklist sets out.
Single-Phase vs Three-Phase at a Glance
| Feature | Single-phase | Three-phase |
|---|---|---|
| Typical pump | Small, garden and smallholding duty | Larger, farm and deep-well duty |
| Starting | Simpler, but harder on larger motors | Smoother, suits larger motors |
| Common voltage | Low-voltage single-phase supply | 380V three-phase supply |
| When it fits | Small volumes, short cable runs | Larger volumes, deep settings, long runs |
Decision Checklist
| Check | What to confirm |
|---|---|
| Motor nameplate | Voltage and phase, read from the plate |
| HP to kW | Convert with the HP-to-kW chart, one unit only |
| Inverter rating | One step above the motor |
| MPPT window | String voltage inside the window, cold morning and hot afternoon |
| Protections | Dry-run and level sensors fitted |
Frequently Asked Questions
How do I know which phase my pump needs?
Read the motor nameplate: it states voltage and phase, and the inverter must match it.
Is three-phase always better?
No: it suits larger motors and larger systems; a small garden pump gains nothing from three-phase power.
Can I run a three-phase pump from a single-phase supply?
Not directly: the motor needs a three-phase output, so the inverter and the supply must both fit the motor.
If the inverter rating is bigger than the motor, does the phase still matter?
Yes: a bigger rating never fixes a phase mismatch, so phase and voltage are checked first, rating second.
What changes when I move from a shallow well to a deep well?
The pump step usually grows, the cable run grows, and the system often steps up to 380V three-phase; re-check the deep-well checklist first.
Send IDEEI the motor nameplate details for a phase and voltage check.