Phase
Single-Phase vs Three-Phase Generators
Single-phase power uses one alternating supply, the kind most houses are wired for. Three-phase power uses three supplies, offset from each other, which is how many commercial and industrial boards are fed. A generator has to match the system it supplies. This page does not explain how to rewire a board or an alternator.
- Match the board
- No rewiring instructions
- The plate states the phase
- Onsite across Gauteng
One supply or three
How do single-phase and three-phase differ?
Single-phase is one live waveform relative to neutral, typically used for houses and small shops. Three-phase is three waveforms. Motors and larger boards are built for it because the power delivery is smoother and the current in each conductor can be lower for the same power.
A house standby set is often single-phase. Offices, warehouses and factories are often three-phase, sometimes with single-phase circuits taken off that board. The generator does not get to ignore the board. If the building is three-phase, a single-phase generator cannot replace the whole supply.
A three-phase generator can feed some single-phase loads, but only within the limits of each phase. Piling the whole building onto one phase overloads that winding while the other two sit lightly loaded. How that is arranged is an electrical design, not a lead moved in the canopy.
Sites and motors
Where each type is used
Residential applications
Most homes are single-phase. A house generator is sized and connected for that supply. A three-phase set is not an upgrade for a single-phase house unless the installation is designed for it.
Commercial applications
Shops and offices may be either. Lifts, HVAC and several distribution boards often mean three-phase. The commercial repair page is the visit. This page is only the phase difference.
Industrial applications
Larger plant is commonly three-phase. Motor loads and higher kVA sit on the industrial pages. Phase is read from the plate before those visits are planned.
Three-phase load balance
The three phases should share the load. One heavily loaded phase can trip or overheat inside a generator that is under its total kVA.
Motor loads
Many motors are three-phase and draw a high current as they start. The running kilowatts understate that moment. Phase and starting current are both part of sizing.
How to identify the phase
Read the data plate: it may say 1-phase or 3-phase, or show a voltage such as 230 V or 400 V. The plate guide explains the fields. Do not identify phase by counting cables if you are not qualified to be in that board.
Single-phase and three-phase compared
A plain comparison. Voltages on a specific site are whatever the plate and the supply say. This table is not a wiring diagram.
| Topic | What changes |
|---|---|
| Supply | Single-phase is one alternating supply. Three-phase is three, offset from each other. |
| Typical sites | Houses are often single-phase. Larger commercial and industrial boards are often three-phase. |
| Motors | Small motors may be single-phase. Larger motors are commonly three-phase and have a high starting current. |
| Using the rating | Three-phase kVA assumes the load is shared. One overloaded phase does not get the full plate figure. |
| Identification | Use the data plate. Do not open a live board to count conductors. |
Supply
Single-phase is one alternating supply. Three-phase is three, offset from each other.
Typical sites
Houses are often single-phase. Larger commercial and industrial boards are often three-phase.
Motors
Small motors may be single-phase. Larger motors are commonly three-phase and have a high starting current.
Using the rating
Three-phase kVA assumes the load is shared. One overloaded phase does not get the full plate figure.
Identification
Use the data plate. Do not open a live board to count conductors.
Related Pages
Sizes, the plate and site types
Google reviews of ProService Generator Repairs
Google Review
Our Hyundai 3-phase diesel unit runs our whole office. They serviced it over the weekend to completely avoid any operational downtime for our staff.
Google Review
When our 3-phase diesel plant started smoking, their heavy-plant mechanics traced the issue to a microscopic crack in an injector line and fitted specialized parts within hours.
Common Questions
Questions about generator phase
What is a single-phase generator?
A set that produces one alternating supply, typically for a house or a small single-phase board.
What is a three-phase generator?
A set that produces three alternating supplies for a three-phase system. Larger commercial and industrial sites often need this.
Can a three-phase generator run single-phase equipment?
Some single-phase loads can be supplied, within the current limit of each phase. The whole load must not be placed on one phase. That arrangement is designed, not improvised.
Can I rewire a single-phase generator to three-phase?
This page does not give rewiring steps. Phase is a property of the alternator and the board. Changing it is an electrical design, not a setting.
How do I tell which I have?
Read the data plate for phase, or for the voltage arrangement. Send a photo of the plate rather than opening the board.
Does phase change the kVA I need?
The kVA still has to cover the load, and on three-phase it has to cover each phase. Balance and motor starting sit beside the total.
My lights are single-phase but the shop is three-phase. Which generator?
The generator has to suit the incoming supply and the board. A single-phase set will not replace a three-phase board. The installation has to be specified properly.
Where does sizing go next?
The sizes page and the kVA-to-kW page. Phase is one input. It is not the whole sizing exercise.
Still unsure what the fault is? Call or WhatsApp 082 057 4605 for onsite diagnosis.
Service Areas
Onsite visits across Gauteng
Technicians travel to the generator. These are the main Gauteng areas. Suburb pages sit under each region.
What to send before we attend
ProService Generator Repairs confirms an onsite visit from these details. Send what you have. A missing model number does not stop the booking.
- Location
- The suburb or site, so the visit can be booked in the right area.
- Make and model
- The generator brand and model, if they are known.
- kVA
- The size printed on the data plate.
- Fuel type
- Diesel, petrol, LPG, natural gas, or dual-fuel.
- Controller model
- The module name on the panel, when it is visible.
- Fault or alarm
- What the set does, and any text on the screen.
- Photos
- The generator, the data plate, and the controller or alarm. Send these on WhatsApp.
Book a Visit
Send the plate, not a cable count
A photo showing phase or voltage is enough. Say whether the building is a house, a shop or a factory.
- Call
- 082 057 4605
- Message us on WhatsApp