Three phase power generators: How to choose the right unit

Three phase power generators are a practical power solution for Australian businesses, farms, workshops, construction sites and rural properties that need to run larger electrical loads reliably. If you have irrigation pumps, welders, cold rooms, compressors, hoists, bore pumps or a 3-phase switchboard, choosing the right generator is not just a matter of “bigger is better”. The correct decision depends on your load type, starting current, fuel preference, installation setup and how often the generator will be used.

This buyer’s guide is designed to help you narrow the field before you speak with an electrician, generator supplier or installer. We’ll cover how three phase units work, when they’re necessary, how sizing is approached, and why diesel generators are commonly chosen for commercial and rural applications across Australia.

Understanding Three Phase Power Generators

What is a three phase power generator?

A three phase generator produces three separate alternating current waveforms that are offset from one another, typically described as being 120 degrees out of phase. This creates a smoother and more efficient supply for many larger motors and industrial loads than single phase power (source).

In Australian settings, three phase supply is commonly associated with 400 V between phases and 230 V from phase to neutral. A three phase generator can be used to run 3-phase equipment directly, supply a 3-phase distribution board, or connect into a professionally installed backup power system with the correct transfer equipment (source).

Why are they used?

Three phase power is valuable because it supports demanding equipment more effectively than standard domestic-style single phase supply. Common Australian examples include:

• Irrigation, bore and transfer pumps on farms and rural properties
• Commercial refrigeration, cold rooms and processing equipment
• Workshop machinery such as welders, hoists, compressors and lathes
• Construction site tools and temporary power distribution boards
• Small industrial plants, warehouses and commercial premises
• Whole-site backup where the existing mains supply is already three phase

The gain is simple: if your business or property depends on equipment that cannot be run from a standard 230 V outlet, a correctly selected three phase generator can help protect productivity, livestock, stock, refrigeration, water supply and site operations during outages or remote work.

Single Phase vs Three Phase Generators - Which Do You Need?

The first decision is whether you need single phase or three phase output. Many buyers start by looking at generator size, but phase type is just as important.

A key point: many three phase power generators can provide both 3-phase and 1-phase outlets. However, the single phase capacity is not usually the full generator rating. As a rough concept, the available single phase load may be limited to around one-third of the total kVA, depending on the generator design and outlet ratings. Always check the generator nameplate, data sheet and supplier guidance before assuming it will run a large single phase load.

If you only have single phase appliances, a three phase generator may not be the best investment. If you have even one critical 3-phase motor or want to back up a 3-phase switchboard, three phase quickly becomes the more appropriate option.

Sizing Your Generator - Key Considerations

Generator sizing is where many expensive mistakes happen. Undersize the unit and you risk nuisance trips, poor motor starting, voltage dip, overheating or unreliable performance. Oversize it significantly and you may spend more than necessary while also running the generator inefficiently at light load.

kVA vs kW

Generators are commonly rated in kVA, while many appliances and motors are labelled in kW. In simple terms, kW is real usable power, while kVA is apparent power. The relationship is:

kW = kVA × power factor

For many commercial and industrial generator applications, a power factor of 0.8 is commonly used as a working assumption. For example, a 20 kVA generator may provide around 16 kW at 0.8 power factor (source). This is a guide only; your actual equipment and generator specification matter.

Running load vs starting load

Running load is the power required once equipment is operating normally. Starting load, also called inrush current, is the short burst of extra power needed to start motors, compressors, pumps and some power tools. Depending on the equipment, starting demand can be several times the running load.

For example, a rural pump that runs comfortably once up to speed may still demand a substantial surge when starting. If the generator cannot support that surge, the pump may fail to start, the generator may stall, or voltage may sag enough to affect other equipment.

Balancing loads across phases

With three phase generators, you also need to consider load balance. Ideally, loads should be reasonably spread across all three phases. If one phase is heavily loaded while the others are lightly loaded, protection may trip or equipment may be stressed.

This is why a proper load schedule is so valuable. A qualified electrician or generator specialist can identify which loads sit on which phase, estimate starting currents, and recommend a suitable generator size and connection method.

A practical sizing approach

As an early planning exercise, you can:

• List every item you want to run from the generator.
• Record each item’s running kW, amps or nameplate rating.
• Identify motors, compressors, pumps and other equipment with high starting demand.
• Decide what must run at the same time and what can be staged manually.
• Add a sensible safety margin, often in the range of 20-30%, before final selection.
• Have the final sizing checked by a qualified professional.

Treat this as a starting point, not a final engineering calculation. Your wiring, switching, earthing, RCD requirements, site layout, duty cycle and local compliance obligations all need professional review.

Diesel Generators - An Efficient Choice

For larger three phase applications, diesel generators are often the default choice. Diesel engines are widely used in commercial, agricultural and industrial generator sets because they are generally efficient under heavier load, durable for regular use, and well suited to motor-starting applications (source).

You may also see them described as diesel electric generators, diesel fuel generators, diesel fuelled generators or, in some listings, diesel fueled generators. The practical question is the same: does the unit provide the phase type, capacity, duty rating and support package your site needs?

Advantages of diesel fuelled generators

• Good efficiency under load: Diesel is often economical for larger or harder-working generator sets.
• Strong duty-cycle suitability: Diesel engines are commonly chosen for frequent, long-duration or commercial use.
• Motor-starting capability: Properly sized diesel sets can be well suited to pumps, compressors and machinery.
• Fuel handling benefits: Diesel is less volatile than petrol, which can be important in commercial and rural settings.
• Availability: Diesel is familiar across farms, worksites and transport operations in Australia.

Limitations to consider

• Weight and size: Diesel units are often heavier than small petrol inverter generators.
• Noise: Acoustic canopies help, but noise planning still matters, particularly near homes, staff areas or livestock.
• Up-front cost: Diesel units can require a larger initial investment, depending on size and configuration.
• Maintenance: Standby systems need periodic exercising, servicing and fuel management so they work when needed.
• Fuel storage: Diesel storage must be managed safely and in line with relevant site requirements.

Petrol generators can suit smaller, occasional-use loads. LPG or natural gas may suit some fixed installations where fuel storage convenience or a gas connection is available, and gas options are discussed further in Mick’s fuel and sizing guide (source). For many larger commercial and rural three phase jobs, though, diesel remains a strong contender.

Choosing the Right Generator for Your Situation

Once you know you need three phase power, the next decision is how the generator will be used. A builder needing mobile site power has different priorities from a dairy farm needing automatic backup for refrigeration and pumps.

Portable generators for temporary or mobile loads

A portable three phase diesel generator can be a practical choice for construction work, mobile maintenance, farm jobs, field welding, temporary pumping and event support. The priority is usually transportability, suitable outlets, rugged build quality and straightforward operation.

When comparing portable diesel fueled generators, check:

• Total kVA and usable kW output
• 3-phase and single phase outlet ratings
• Fuel tank size and expected run time under load
• Noise rating and whether an acoustic enclosure is included
• Weight, lifting points, wheels or skid base
• Whether the diesel generator is suitable for your intended duty cycle

If you are actively comparing options, Mick’s range of generator sales can be a useful starting point for seeing available styles and capacities without locking yourself into a final decision before professional sizing.

Standby generators for backup power during outages

Standby systems are designed to support critical loads when mains power fails. This might include a cool room, office systems, pumps, security, communications, medical or veterinary equipment, or essential farm infrastructure.

In standby applications, the generator is only one part of the system. You may also need:

• An automatic or manual transfer switch
• A compliant connection to the switchboard
• Load shedding or staged starting
• Weather protection and ventilation
• Routine testing and servicing
• Fuel storage planning and maintenance

When people search for “generators diesel” for backup use, they are often comparing engine reliability, fuel efficiency, canopy noise, automatic start compatibility and service support. These are all worth considering alongside the headline kVA rating.

Prime or off-grid power

Prime power means the generator is expected to run for long periods as a main source of electricity, rather than simply sitting in standby. This can apply to remote sheds, rural worksites, temporary camps, off-grid businesses and properties waiting for grid connection.

For prime use, pay close attention to:

• The generator’s prime rating versus standby rating
• Fuel consumption over long operating hours
• Service intervals and local parts support
• Cooling and ventilation in Australian summer conditions
• Noise impact over extended operation
• Integration with batteries, solar or hybrid systems if relevant

Diesel fuel generators can perform well in these roles, but they must be selected for the actual duty. A unit intended for occasional standby may not be the right choice for daily long-hour operation.

Buying Checklist for Australian Businesses and Rural Properties

Before purchasing, use this checklist to sharpen your requirements:

• Confirm phase type: Do you need 230 V single phase, 400 V three phase, or both?
• List critical loads: Separate “must run” loads from “nice to have” loads.
• Identify motor loads: Pumps, compressors, refrigeration and machinery may need high starting capacity.
• Check duty rating: Is the unit for portable, standby, prime or continuous-style use?
• Plan installation: Who will handle wiring, transfer switching, earthing and compliance?
• Consider noise and location: Think about neighbours, staff, livestock, ventilation and access for servicing.
• Review fuel logistics: How much diesel will you store, how often will it be used, and how will it be managed?
• Ask about support: Warranty, servicing, spare parts and supplier advice matter after the sale.

The risk in buying too quickly is ending up with a generator that looks right on paper but struggles with your real site conditions. The promise of a better process is simple: understand your loads first, then choose the generator.

Frequently Asked Questions

Do I need a three phase generator if my property has three phase mains?

Not always. If you only want to run a few single phase appliances, a single phase generator may be enough. However, if you want to back up a 3-phase switchboard or run 3-phase equipment, you will generally need a three phase generator and a professionally designed connection arrangement.

Can a three phase generator run single phase appliances?

Many can, but the available single phase capacity is limited by the generator design and outlet rating. You cannot assume the full kVA rating is available from one single phase outlet. Check the data sheet and get advice before connecting large single phase loads.

What size three phase generator do I need?

It depends on your running load, starting load, power factor, phase balance and duty cycle. As an early guide, list your equipment, total the loads that must run together, allow for motor starting, then add a safety margin. Final sizing should be confirmed by a qualified electrician or generator specialist.

Are diesel generators better than petrol generators?

Diesel generators are often preferred for larger, heavier-duty commercial and rural applications because they tend to suit sustained load and motor-starting work well. Petrol generators can still be suitable for smaller, lighter or occasional-use jobs. The right choice depends on load size, run time, fuel handling, budget and support needs.

Can I connect a generator directly to my switchboard?

Only through a compliant installation completed by a licensed electrical professional. Direct or improvised connections are dangerous and may be illegal. Transfer switches, isolation, earthing, RCD protection and local rules must be properly addressed.

How often should a standby diesel generator be tested?

Standby generators should be exercised and serviced according to the manufacturer’s instructions and site requirements. Regular testing helps identify battery, fuel, coolant, oil or control issues before an outage occurs.

Conclusion

Three phase power generators are an important investment for Australian businesses, farms, workshops and remote sites that depend on larger electrical loads. The right unit can support productivity, protect stock, keep pumps running and reduce downtime during outages. The wrong unit can leave you with frustrating starting problems, unbalanced phases, excess fuel use or compliance issues.

Start with the basics: confirm whether you truly need three phase, calculate your running and starting loads, decide whether the generator is for portable, standby or prime use, and compare diesel, petrol or gas options based on the job. For many commercial and rural buyers, diesel electric generators remain a strong choice, particularly where durability and higher-load operation matter.

Before purchasing or installing, speak with a qualified electrician, generator installer or experienced supplier. A short professional review can save you from a costly mismatch and help ensure the system is safe, compliant and fit for purpose.

Disclaimer

This article provides general guidance only and does not replace professional electrical, engineering, safety or compliance advice. Generator sizing, installation, electrical connections, transfer switches, earthing, RCD protection, fuel storage and regulatory compliance must be assessed by qualified professionals. Non-experts should not carry out electrical wiring work. Always follow local codes, manufacturer instructions and best safety practices when purchasing, installing and operating a generator.

Information is provided in good faith and may change without notice. Mick’s Gone Bush is not responsible for inaccuracies, omissions, changes in product specifications, or decisions made based on this general information. Pricing has not been provided because generator costs vary significantly by size, configuration, model, features and installation requirements.

About the Author

Mick’s Gone Bush is an Australian generator and back-up power distributor supporting customers across business, rural, trade and remote-area applications. Our content is written to help buyers understand practical generator selection considerations, including fuel type, sizing, portability, standby use and safe installation planning. For final product selection and electrical work, we always recommend consulting qualified professionals.

Sources and Further Reading

• Three phase power concepts, generator sizing basics, kVA/kW relationship, fuel selection considerations and Australian generator use cases: Mick’s Gone Bush gas generator buyer guide