Three-phase generator amps are not a fixed number. They depend on the rating and the voltage, so a 100 kVA set delivers about 152 A at 380 V, about 144 A at 400 V, about 139 A at 415 V, and about 120 A at 480 V. Same machine, same rating, four different current figures.
That is the part most conversion charts leave out. A chart that lists one column of amps is only correct for the voltage it was built around.
This article gives you the full chart across the voltage classes we build for, in both directions: the current a set delivers at a given rating, and the rating you need for a current you already have. Then it covers the three ways that number gets misread, because two of them are expensive.
We build three-phase sets from small industrial units to 3,000 kW machines, and the figures below are worked out for every voltage class we build for rather than copied from a single-voltage chart.
Need the current worked out for a specific set and site voltage? Send us the rating and the voltage and we will give you the figure directly. Talk to our engineering team →
Key Takeaways
- Three phase generator amps depend on voltage as much as on rating. A 100 kVA set gives 152 A at 380 V and 120 A at 480 V.
- Current is set by the kVA rating, not the kW rating. Power factor changes the usable kW, not the amps the alternator delivers.
- The figure is the current in each line, not the total. Adding the three line currents of a 100 kVA set gives 432 A, which is three times the right answer.
- You can work the other way too. A 250 A supply at 400 V supports about a 173 kVA set, and about 208 kVA at 480 V.
- Below 415 V the current rises sharply for the same rating, which is why 50 Hz sites need heavier switchgear than the kVA figure suggests.
Three Phase Generator Amps: The Full Chart by Voltage
Start with the chart, because it answers the question directly and shows the problem simultaneously.
The Chart
Current in each line, for common ratings, at the four voltage classes we build for:
| Generator rating | 380 V | 400 V | 415 V | 480 V |
|---|---|---|---|---|
| 50 kVA | 76 A | 72 A | 70 A | 60 A |
| 100 kVA | 152 A | 144 A | 139 A | 120 A |
| 250 kVA | 380 A | 361 A | 348 A | 301 A |
| 400 kVA | 608 A | 577 A | 556 A | 481 A |
| 630 kVA | 957 A | 909 A | 876 A | 758 A |
| 1,000 kVA | 1,519 A | 1,443 A | 1,391 A | 1,203 A |
Read down a column and you have the current for every rating at that voltage. Read across a row and you have the same set at four different voltages, which is the same machine asked to deliver the same power into a different electrical system.
Why Does the Same kVA Give Different Amps?
Current and voltage trade against each other. For a fixed amount of power, raising the voltage lowers the current, and the two move in proportion.
Every figure in the table follows from one relationship, which our three phase diesel generator guide sets out in full. The point of publishing it as a chart is that you do not have to work it out on site. It is also worth knowing that charts built for the North American market, such as Cummins’ rental amp chart, stop at the 208 V, 240 V and 480 V classes. A US-sourced chart is the wrong reference for a 400 V site.
Going from 480 V to 380 V raises the current by about 26% at every rating in the table. That is not a rounding difference. It is the difference between a switchgear order that fits and one that has to be rebuilt, and it is the single most common reason a current figure gets quoted wrongly in a tender.
The narrower spread is worth knowing too. Between 380 V and 415 V, the two ends of the European 50 Hz band, the current moves about 8%, which is 128 A at 1,000 kVA.
Working Backwards: From Amps to kVA
Most buyers arrive at this from the opposite direction. They already have a supply, service, or switchgear rating in amps, and they need to know what generator that supports.
The Reverse Relationship
Working backwards means multiplying the current by 1.732 and by the voltage, then dividing by 1,000. The result is the kVA that current represents.
Here it is already done, so you can read your own figure off the table:
| Available current | 380 V | 400 V | 415 V | 480 V |
|---|---|---|---|---|
| 100 A | 66 kVA | 69 kVA | 72 kVA | 83 kVA |
| 200 A | 132 kVA | 139 kVA | 144 kVA | 166 kVA |
| 250 A | 165 kVA | 173 kVA | 180 kVA | 208 kVA |
| 400 A | 263 kVA | 277 kVA | 288 kVA | 333 kVA |
| 630 A | 415 kVA | 436 kVA | 453 kVA | 524 kVA |
The voltage question matters more here than anywhere else. A 250 A supply supports about 173 kVA at 400 V, but about 208 kVA at 480 V. Ask for a set sized from the amps figure without stating the voltage, and you can be handed a machine that is a fifth too small.
A Supply Figure Is Not a Load Figure
Rosalind priced a standby set for a plastics workshop by starting from the incoming supply. The site had a 250 A feed at 400 V, which turns into roughly 173 kVA. She asked suppliers for a 200 kVA set and expected the quotes to be close.
They were not, and the reason was not the price. Two suppliers asked which voltage the 250 A was measured at, and one asked whether the 250 A was the supply rating or the measured running load. It was the supply rating, and the actual running load was nearer 140 A.
The set was sized from the supply, not the load, and the correct rating was smaller than the one she had been quoting. The voltage and the source of the amps figure moved the answer more than any supplier’s pricing did.
Sizing from a supply figure rather than a load list? Send us both and we will show you where they diverge.
Why You Do Not Size at the Exact Figure
Sizing a set so its rated current exactly matches your required current is a mistake, for a simple reason: the rated current is a limit, not a target.
A set run continuously at its rated current has nothing left for the moments when a load draws more than its steady-state figure, and nothing in reserve for equipment added later. That is why the recommendation that comes out of a sizing exercise is always above the bare number the table gives you.
How much above depends on what the load actually does, and that is a sizing question rather than a current question. Engine manufacturers work from the same principle: Caterpillar’s engine and generator sizing guide and Cummins’ application manual both size the machine outward from the load rather than from a current figure. Our industrial diesel generator guide covers the rating side of it.
Once you have the current figure, what you do with it next is a different job. Choosing the cable and protective device that will carry and clear that current correctly is a site-specific exercise covered in our generator electrical connection guide. This article stops at the current itself.
The Three Numbers People Misread
The chart is simple. The mistakes around it are not, and they follow a pattern.
Per-Phase Current Is Not the Sum of Three Phases
This is the most expensive one. A three-phase set delivers its current through three lines, and the figure in the chart is what flows in each of them.
Read the chart as a total and you get the wrong answer by a factor of three. A 100 kVA set at 400 V shows 144 A. Add the three lines together and you get 432 A, which is not a bigger version of the right answer. It is simply the wrong quantity.
Marek hit this while specifying switchgear for a workshop extension. He had the 100 kVA figure from the chart, multiplied it by three, and specified the panel for 432 A. The panel was oversized by a factor of three, and the quote that came back was rejected before anyone checked the arithmetic. The correct specification was 144 A per line, and the cost difference between the two was the whole reason the project stalled for a month.
kVA Sets the Amps; Power Factor Sets the Usable kW
The second misreading is about power factor, and it is widespread enough to be worth stating plainly.
The current a set delivers is set by its kVA rating. Its kW rating does not set it, and it does not change when the load’s power factor changes. A 100 kVA set at 400 V delivers about 144 A per line whether the load runs at 0.8 power factor or at unity.
What the power factor changes is how much of that current you can turn into useful work. A 100 kVA set at 400 V delivers about 144 A per line at 0.8 power factor, and the same 144 A at unity. The current does not move; the useful kilowatts behind it do.
How that splits into real power is the kVA-versus-kW relationship, covered properly in our kVA vs kW generator guide. For this article, the point is narrower: do not adjust the current figure for power factor.
One Sentence on Single Phase Against Three Phase
At the same kVA and the same voltage, a single-phase supply needs about 1.73 times the current of a three-phase one, which is why large sites run three-phase. The machine-level comparison behind that figure is covered in our single phase vs. three-phase generator guide.
What Changes the Current, and What Does Not
One more set of distinctions, because they decide whether the chart applies to your site at all.
What Does Not Change It
Frequency does not change it. A set giving 144 A per line at 100 kVA and 400 V gives the same 144 A at 50 Hz or at 60 Hz, because the relationship between power, voltage and current does not involve frequency.
What Does Change It
Two things move the current in practice. The first is the voltage the set actually operates at, which is the whole subject of this article.
The second is the condition of the machine and the site. A set’s rated current assumes the conditions it was rated for, and the mechanisms that reduce it beyond those conditions are thermal rather than arithmetic. Our generator alternator specifications guide covers the ratings and the thermal limits behind them.
Working at a site voltage that is not in the chart? Tell us the voltage and the rating and we will give you the current figure. Ask our engineers →
Three Phase Generator Amps: Common Questions
How many amps is a 100 kVA three-phase generator?
It depends on the voltage. A 100 kVA three-phase generator delivers about 152 A per line at 380 V, 144 A at 400 V, 139 A at 415 V, and 120 A at 480 V. The 400 V figure of 144 A is the one quoted most often, which is why it is worth knowing that it is voltage-specific rather than universal.
How do I convert kVA to amps for a three-phase generator?
Read it off the chart above: pick your voltage column, then your rating row. That is why the table is laid out by voltage rather than as a single list of amps, and reading it directly avoids the arithmetic error that hand calculation invites.
What size generator do I need for a 200 amp service?
A 200 A supply supports roughly 139 kVA at 400 V, or about 166 kVA at 480 V. That is the conversion, not the recommendation: the set you buy should be larger than the bare figure, by an amount that depends on the load.
Does power factor change the amps?
No. The current is set by the kVA rating and the voltage. Power factor changes how much real power (kW) you get from that current, not how much current the set delivers.
Conclusion
Three-phase generator amps come down to four things:
- Voltage matters as much as rating. A 100 kVA set is 152 A at 380 V and 120 A at 480 V, a 26% spread.
- Read the chart per line, not as a total. Adding the three line currents is wrong by a factor of three.
- kVA sets the current; power factor sets the usable kW. Do not adjust the amps figure for power factor.
- Work backwards when you need to. From a supply in amps, multiply by 1.732 and by the voltage, then divide by 1,000.
If you take one thing from this, take the question to ask before any of the arithmetic. Ask which voltage the current is measured at, and whether the figure came from a supply rating or a running load. Those two questions change the answer more than any other input, and they cost nothing to ask.
