A country name does not replace site electrical data. One facility may contain single-phase lighting, three-phase motors and several voltage levels. The wrong phase, wiring or neutral arrangement can prevent connection or create overvoltage and protection problems.
Use load plates and the existing single-line diagram to define line voltage, phase voltage, phases, wires and grounding. A three-phase set can serve single-phase loads only within phase-current and neutral-current limits.
1. Understand what this decision changes
Line voltage and phase voltage are not the same
In a common three-phase four-wire wye system, line-to-line and line-to-neutral voltages differ. One voltage number in a quotation is not sufficient.
Load architecture determines phase count
Large motors are commonly three-phase while lighting and receptacles are often single-phase, creating a need for a four-wire source.
Imbalance limits usable capacity
Concentrated single-phase loads may reach phase-current, negative-sequence or neutral-current limits before total kW is used.
2. Inputs to confirm before procurement
Collect complete load plates and the single-line diagram, distinguishing line-to-line from line-to-neutral voltage.
- Load voltage, phase, frequency and connection
- Quantity and capacity of three-phase and single-phase loads
- Existing bus, ATS, breaker and cable wiring
- Neutral switching, grounding and protection concept
- Worst simultaneous distribution of single-phase loads
3. How the main options compare
| Option or parameter | Where it fits | What must be verified |
|---|---|---|
| Single-phase output | Smaller isolated systems where every critical load is single-phase. | Starting current, line current and single-phase alternator rating. |
| Three-phase three-wire output | Specific industrial systems with three-phase loads and no neutral requirement. | Grounding, protection, auxiliaries and control-power source. |
| Three-phase four-wire output | Common sites combining motors with lighting, receptacles and controls. | Line voltage, phase voltage, neutral size and balance. |
4. The most common decision errors
Common mistakes
- Assuming every 380 V or 480 V load is three-phase
- Checking line voltage but not line-to-neutral voltage
- Using the full three-phase rating on any single phase
- Leaving ATS neutral switching and grounding undefined
Trace the voltage system from generator terminals to final loads, including transformers and transfer equipment.
5. What the technical specification must state
The specification should state at least
- Line-to-line and line-to-neutral voltage, phases and wires
- Frequency, winding connection and reconnection range
- Allowed phase current and imbalance
- Neutral terminal, size, switching and grounding
- Protection settings, phase sequence and voltage monitoring
“Local standard voltage” is not a complete technical specification.
6. How to verify and make the final decision
Verification and acceptance
- Cross-check generator, ATS, switchboard and load nameplates
- Measure all line and phase voltages
- Record phase currents and neutral current
- Check phase sequence and motor rotation
- Test the worst unbalanced operating combination
Choose the voltage system that directly matches existing distribution and critical loads, minimizing temporary transformers and field reconnection.
If multiple voltages are required, define whether they come from reconnectable windings, a transformer or independent outputs, with clear interlocks and protection.