Single phase generator sizing matches the set's rating to the real site load, so a buyer gets a machine that starts motors without tripping. Tesla Power sizes every enquiry from the load list, then returns a scoped quote so you can compare suppliers before ordering.
- Build the load list first, then choose a rating from that list.
- Apply a demand factor because tools and lights rarely run at once.
- Confirm voltage and frequency before the set is built.
- Ask the Chinese single phase generator manufacturer for the subtransient reactance figure.
Why single phase generator sizing starts with the load list
The load list is the only input that decides the rating. A sizing exercise that begins with a favourite frame size usually ends with a set that is too small for the motor start or too large for the budget. We start every enquiry from the connected equipment, because that list survives a change of supplier. See the generator product range for the frames we build.
Write down each circuit, its running watts, and whether it starts hard. A 10kVA lighting circuit and a 10kVA air compressor draw the same running power, yet the compressor's start current is far higher. That starting current is what the alternator must tolerate. Start with the load list, because a number on paper is cheaper to fix than a tripped breaker on site. A set sized without it will trip on the first motor it meets.
What load types change a single phase generator sizing?
Resistive loads such as heaters and lamps draw current in phase with voltage, so their kVA and kW are almost equal. A sizing for a lighting-only shed can use the watt sum almost directly. The set still needs headroom for the start, but the arithmetic stays simple and the voltage dip stays small. A set for workshop use keeps this case easy to verify before the first motor is added.
Motor loads tell a different story. An induction motor pulls a high inrush current and a lagging power factor, which pushes the kVA well above the kW. A set in a workshop therefore needs an alternator sized for the start, not the run. A soft starter or a correctly sized frame removes the trip. Tesla Power Equipment quotes both figures on the offer so the buyer sees the gap and can plan the cable size.
How the load settles the phase choice
The load decides the phase, not the other way round. The phase choice is settled by what the site already has: a 230V distribution board points to single phase, while a 400V three-phase board needs the three-phase machine. Forcing a three-phase set onto a single-phase site wastes two of its three windings and complicates the transfer switch.
Sets of this size suit small sites where the largest load is one motor or one compressor. A three-phase set suits workshops with several motors, any lift, pump or chiller. A set of this size for a small business often costs less to buy and to house, while a three-phase machine earns its keep only when the load is balanced across phases. Read our three-phase sizing guide before assuming bigger is better.
A single phase generator for export sites ships with the same documentation as the three-phase range, so the only real difference is the winding. Tesla Power applies the same factor rule across every export order, so the phase choice does not change the arithmetic that follows it.
How do you apply a demand factor to the load list?
A demand factor prevents you from paying for capacity the site does not use. Few sites run every tool at the same instant, so the connected total overstates the true need. A sizing that omits the factor often lands on a frame one size too large, which raises both price and fuel burn at part load. A frame chosen this way also matches the cable and breaker the site already has.
Use a factor of 0.75 to 0.9 for mixed workshop loads and keep it closer to 1.0 for continuous process loads. Apply it to the connected watts, then add the largest motor start on top. The open-frame range we build covers the common single-phase frames, so the factor mostly decides which frame, not whether one exists. Send the load list to our engineering team for a scoped quote that already carries the cable and breaker sizes.
Worked single phase generator sizing example
Take a workshop with a 10kVA lighting and tool circuit plus a 10kVA compressor that starts hard. Connected load = 10kVA + 10kVA = 20kVA. The largest motor start and a demand factor point to the 30kVA frame, which leaves margin for both. At 0.8 power factor the real power = 30kVA x 0.8 = 24kW. At 230V single phase the full-load current = 30000 / 230 = 130A.
That single calculation settles four decisions: the frame size, the alternator kVA, the cable ampacity and the breaker rating. It also shows why a 10kVA set would be short by roughly a third of the true need. Send the same schedule to our engineering team and the quote returns with the cable and breaker already specified, which removes the most common site-side mistake. The load factor explainer shows why running near the kVA rating also trims fuel cost at the duty point the buyer actually runs.
What rating class does ISO 8528-1 assign the set?
ISO 8528-1 defines the rating class that every set is built to, and the class decides how many hours the machine may run. A sizing for a standby site usually lands on class G2 or G3, while a prime-power site needs the higher class with the matching maintenance interval. The class is not a suggestion; it sets the allowable overload and the service life.
The ISO 8528-1 standard also fixes how the rating is measured, so two suppliers quoting the same class mean the same thing. A single phase generator manufacturer who quotes without a class leaves the buyer guessing which number applies. Tesla Power states the class on every data sheet, because a rating with no class is a rating no one can commission against.
| Set rating (kVA) | Real power at 0.8 pf (kW) | Full-load current at 230V (A) |
|---|---|---|
| 20kVA | 16kW | 87A |
| 30kVA | 24kW | 130A |
| 50kVA | 40kW | 217A |
How does power factor change the kVA you order?
Power factor is the ratio of real power to apparent power, and it decides how much kVA a given load needs. A sizing at 0.8 power factor means the set must carry 25% more kVA than the kW it delivers. A site that quotes only kW may order a frame too small to start its own motors.
State the power factor on the enquiry and let the supplier size the alternator, not just the engine. A 20kVA set at 0.8 delivers 16kW; the same frame at unity would deliver 20kW but would need a different excitation setting. Our our company profile lists the alternator types we fit, and the quote shows both the kW and the kVA so the buyer sees the margin. Tesla Power quotes both figures on every offer so the gap stays visible.
Which standards shape a single phase generator specification?
Several standards turn a load list into a buildable specification. ISO 3046 sets the reference condition, so altitude and ambient temperature are stated against a common baseline. A single phase generator for tropical or high sites needs that derating written down, or the rated output at the real site will not match the nameplate.
For standby applications the NFPA 110 requirements set the pickup time and the testing expectation, while IEC 60947-2 governs the breaker that protects the output. Where the set ships into the EU, the (EU) 2016/1628 emissions regulation sets the engine tier. Conformity assessment for the EU market gathers these into one file, and Tesla Power Equipment keeps that file with the handover pack so auditors find every figure in one place.
CE marking requirements for the single phase generator sit inside that same conformity file, alongside the emissions evidence and the machinery paperwork. Ask for the full set before the set leaves the factory, because a missing document is cheaper to add at build time than to chase after shipment.
Site conditions that derate a single phase set
Altitude and ambient heat cut the available output, and the cut is real even on a small set. Per ISO 3046 the reference condition is around 25C and near sea level, so a site at 1500m or 40C loses a few percent of its rating. A sizing that ignores this arrives short on the hottest afternoon of the year.
Add the derate to the load, do not subtract it from the margin. If the site needs 20kVA at the load and the nameplate loses 5% at altitude, specify the next frame up rather than hope the engine over-delivers. Tesla Power states where each set sits on its own derate curve in the handover pack, so the site team can confirm the true output before commissioning begins.
Common single phase generator sizing mistakes
The first mistake is sizing from connected watts and forgetting the motor start. The second is quoting only kW, which hides the kVA the alternator must carry. The third is skipping the demand factor, which lands on an oversized frame that burns more fuel at part load than the site ever needs.
A fourth error is treating voltage as fixed. A 120V region and a 230V region need different sets, and mixing them strands the buyer with the wrong breaker. Our help and advice section carries the regional voltage notes, and the fuel per kWh notes show why the frame size also moves the running cost. Tesla Power flags all four on the enquiry form so none slips through to the build stage.
Frequently asked questions about single phase generator sizing
Add the running watts of every tool, apply a demand factor near 0.8, then add the largest motor start on top. A typical small workshop lands on a 10kVA or 20kVA frame at 0.8 power factor. Confirm the starting current of the biggest motor, because that figure, not the running watts, often decides the frame.
Yes, many single phase sets offer a 120/240V tap that splits the winding, so both voltages are available at once. The total load must still stay inside the kVA rating. A Chinese single phase generator supplier can build the tap configuration to match the site distribution board.
Power factor is the gap between the kW you use and the kVA the alternator carries. At 0.8 the set needs 25% more kVA than kW, so a kW-only quote can pick a frame too small for the start. State the power factor on the enquiry so the supplier sizes the alternator, not just the engine.
Per ISO 3046 the reference is near 25C and sea level, so a site at 40C or 1500m loses a few percent. Add that loss to the load rather than trimming the margin. A set at a high or hot site should step up one frame so the real output still meets the need.
For any building with a utility supply, yes. The transfer switch isolates the grid before the generator connects, which protects line workers and the alternator. IEC 60947-2 governs the protective device, and the NFPA 110 requirements set the pickup time for standby use.
Ask for the data sheet with the rating class, the subtransient reactance, the derate curve and the test record. CE marking requirements for the single phase generator sit in the conformity file alongside the emissions evidence. Tesla Power ships these in the handover pack so the site team can commission against them without chasing separate documents.
No. An oversized set runs at low load, which raises wet-stacking risk and wastes fuel, while an undersized set trips on motor start. The right frame is the one that meets the load plus the start with a small margin. Size from the load list, not from caution, and the result is both reliable and cheaper to run.