Generator Sizing Chart: kVA to Amps Conversion for 50 Hz and 60 Hz Power Systems

A Generator Sizing Chart answers one question quickly: how much current will this machine actually deliver at my system voltage. Getting that number right determines cable sizing, breaker selection, busbar rating and switchgear specification. Getting it wrong shows up later as overheated conductors, nuisance tripping, or a plant that cannot accept the load it was built for.

The arithmetic is not difficult. What causes errors in practice is applying a chart built for one part of the world to a site in another. Most published generator sizing tables are North American, listing 208 V, 240 V and 480 V at 60 Hz. Most of Africa, Europe, the Middle East and Asia runs 380 V, 400 V or 415 V at 50 Hz. A chart without those columns is not usable on a Sahel mine site or a Gulf industrial plant.

This Generator Sizing Chart covers both. Your project is the hero here. USP&E Global works as the guide, and across 25 years, 150+ projects and 35+ countries we have sized, installed and operated generating plant on both frequencies.

The Formulas Behind Any Generator Sizing Chart

Three relationships do all the work. Every figure in the tables below derives from them.

Three phase current from kVA:

Amperes = kVA multiplied by 1000, divided by (Volts multiplied by 1.732)

Three phase current from kW:

Amperes = kW multiplied by 1000, divided by (Volts multiplied by 1.732 multiplied by power factor)

Single phase current from kW:

Amperes = kW multiplied by 1000, divided by (Volts multiplied by power factor)

Two definitions prevent most mistakes. kVA is apparent power, the total the alternator must supply. kW is real power, the useful work delivered. They are linked by power factor, so kW equals kVA multiplied by power factor. Standard industrial generating sets are rated at 0.8 power factor, which is why an 800 kW machine is a 1000 kVA machine.

Working from kVA is safer than working from kW, because the kVA figure already contains the power factor assumption. If you size cable from a kW figure and forget to divide by power factor, you will undersize the conductor by 20 percent.

A note on voltage that catches people out. In a three phase formula, the voltage used is always the line to line value. On a 400Y/230 V system that is 400, not 230. On a 480Y/277 V system it is 480, not 277. Substituting the line to neutral value produces a number that is roughly 1.73 times too high and corresponds to nothing physical.

Generator Sizing Chart for 50 Hz Systems: 380 V, 400 V, 415 V and 11 kV

These are the standard distribution voltages across most of Africa, Europe, the Middle East and Asia. Figures are three phase line current at the stated line to line voltage, calculated from kVA.

Generator Rating (kVA)	Output at 0.8 PF (kW)	Amps at 380 V	Amps at 400 V	Amps at 415 V	Amps at 11 kV
10	8	15	14	14	0.5
20	16	30	29	28	1.0
30	24	46	43	42	1.6
50	40	76	72	70	2.6
75	60	114	108	104	3.9
100	80	152	144	139	5.2
150	120	228	217	209	7.9
200	160	304	289	278	10.5
250	200	380	361	348	13.1
350	280	532	505	487	18.4
500	400	760	722	696	26.2
750	600	1140	1083	1043	39.4
1000	800	1519	1443	1391	52.5
1250	1000	1899	1804	1739	65.6
1500	1200	2279	2165	2087	78.7
2000	1600	3039	2887	2782	105.0
2500	2000	3798	3608	3478	131.2

 

The 11 kV column matters more than its small numbers suggest. Above roughly 2 MW, low voltage distribution becomes impractical because the conductor sizes required are enormous. A 2500 kVA machine draws 3,798 A at 380 V and only 131 A at 11 kV, which is the entire argument for medium voltage generation on larger mining and utility installations.

Generator Sizing Chart for 60 Hz Systems: 208 V, 240 V, 480 V and 4160 V

These voltages apply across North America, parts of South America, Saudi Arabia and Liberia, among others.

Generator Rating (kVA)	Output at 0.8 PF (kW)	Amps at 208 V	Amps at 240 V	Amps at 480 V	Amps at 4160 V
10	8	28	24	12	1.4
20	16	56	48	24	2.8
30	24	83	72	36	4.2
50	40	139	120	60	6.9
75	60	208	180	90	10.4
100	80	278	241	120	13.9
150	120	416	361	180	20.8
200	160	555	481	241	27.8
250	200	694	601	301	34.7
350	280	972	842	421	48.6
500	400	1388	1203	601	69.4
750	600	2082	1804	902	104.1
1000	800	2776	2406	1203	138.8
1250	1000	3470	3007	1504	173.5
1500	1200	4164	3608	1804	208.2
2000	1600	5551	4811	2406	277.6
2500	2000	6939	6014	3007	347.0

 

Frequency conversion is a live commercial question for buyers sourcing surplus equipment. Many 1500 and 1800 rpm reciprocating sets can be converted between 50 Hz and 60 Hz, and certain aeroderivative units switch between frequencies readily. Gas turbines from other manufacturers are considerably more involved. Available inventory across both frequencies is published on the USP&E listings, including diesel and natural gas platforms.

Single Phase Generator Sizing Chart

Single phase generating sets occupy a much narrower band than three phase machines. Standard product effectively stops around 50 kVA, and anything larger offered as single phase warrants close scrutiny of the alternator configuration. The figures below are calculated at 0.8 power factor for consistency with the three phase tables above.

Generator Rating (kVA)	Output at 0.8 PF (kW)	Amps at 120 V	Amps at 230 V	Amps at 240 V
5	4	42	22	21
10	8	83	43	42
15	12	125	65	62
20	16	167	87	83
25	20	208	109	104
30	24	250	130	125
40	32	333	174	167
50	40	417	217	208

 

The current figures in the 120 V column explain why single phase is confined to small ratings. A 50 kVA machine at 120 V draws 417 A, which already demands substantial conductors for a modest amount of power. For industrial and mining applications, three phase is effectively always the correct answer.

Why a Generator Sizing Chart Is Only the Starting Point

A chart gives the nameplate current at reference conditions. Real sites are not reference conditions, and three adjustments almost always apply.

Altitude and ambient temperature derate the machine. Manufacturers publish output at ISO 8528 reference conditions. A site at 1,200 metres on the Katanga plateau, or at 45 degrees Celsius ambient in the Gulf, will not achieve nameplate. Derate curves differ by platform, and a set sized from a chart alone can arrive materially short.

Motor starting current dominates the sizing calculation. A direct on line motor draws six to eight times full load current during start. On sites with large pumps, crushers or compressors, the generator is frequently sized by the starting transient rather than the running load, which is a different and larger calculation than any chart provides.

Non linear loads change the requirement. Variable speed drives, rectifiers and UPS systems draw harmonic current that heats the alternator without doing useful work. Alternator oversizing is commonly required where these dominate the load profile.

Site Factor	Typical Effect on Sizing	Correct Response
Altitude above 1000 m	Progressive output derate	Request platform derate curve for site elevation
Ambient above 40 degrees C	Progressive output derate	Size from site design temperature, not ISO
Direct on line motor starting	6 to 8 times full load inrush	Perform transient study, consider soft starters
Harmonic and non linear load	Additional alternator heating	Oversize alternator, review harmonic mitigation
Duty rating mismatch	Early overhaul, warranty rejection	Match standby, prime or continuous rating to hours

 

Regional demand and reliability context for these markets is published in the IEA Africa Energy Outlook and the World Bank energy data portal, with financing context available from the African Development Bank energy programme. Where hybrid integration is planned, IRENA publishes guidance on renewable integration into thermal systems.

Proven Sizing and Installation Experience Behind This Generator Sizing Chart

USP&E’s documented project record covers sizing, installation and long term operation across both frequencies and a wide capacity range.

Mali, Loulo Gounkoto complex. USP&E refurbished 80 MW of Caterpillar engines and installed 24 MW of new Cat 12CM32 engines at a large gold mining complex in western Mali, with the company’s own case study recording substantially improved reliability and availability.

Mali, Syama Gold Mine. USP&E delivered a 30 MW Caterpillar power station installation for the Syama operation, managed by Société des Mines de Syama S.A.

Tanzania, Golden Pride Mine. At this gold mine operated by Resolute Mining, a power station combining two engine brands with incompatible controls was producing severe harmonic distortion, degrading reliability across the distribution network. USP&E upgraded the control system to restore stable power distribution, which is precisely the class of problem that sizing calculations alone do not reveal.

Further verified detail is available through the USP&E project portfolio and the power plant engineering practice.

Frequently Asked Questions: Generator Sizing Chart and kVA to Amps Conversion

How do I convert kVA to amps for a three phase generator?

Multiply the kVA rating by 1000, then divide by the system line to line voltage multiplied by 1.732. For a 500 kVA generator at 400 V, that gives 500,000 divided by 692.8, which is approximately 722 A per phase. Always use the line to line voltage in this formula, never the line to neutral value.

What is the difference between kVA and kW on a generator?

kVA is apparent power, the total load the alternator must supply. kW is real power, the useful work delivered to the load. They are related by power factor, so kW equals kVA multiplied by power factor. Standard industrial generating sets are rated at 0.8 power factor, which is why a 1000 kVA set is described as an 800 kW set.

How many amps does a 100 kVA generator produce?

At 400 V three phase, a 100 kVA generator delivers approximately 144 A per phase. At 380 V the same machine delivers about 152 A, and at 415 V about 139 A. At 208 V, 60 Hz it delivers roughly 278 A. Current rises as voltage falls for the same kVA rating, which is why cable sizing must always reference the actual system voltage.

Why do generator sizing charts show different amps for the same kVA?

Because current depends on voltage. A fixed kVA rating produces higher current at lower voltage and lower current at higher voltage. Charts also differ in whether they work from kVA or from kW, and a kW based chart embeds a power factor assumption that may not match your machine. Confirm which basis a chart uses before relying on it.

Does altitude affect generator output?

Yes, significantly. Manufacturers rate output at ISO 8528 reference conditions, and both altitude and elevated ambient temperature reduce achievable output. Sites above roughly 1,000 metres and ambient temperatures above 40 degrees Celsius both require derate factors specific to the engine platform. Always request the derate curve for your site elevation and design temperature rather than sizing from nameplate.

Should I size a generator from running load or motor starting current?

On sites with large direct on line motors, starting current usually governs. A motor can draw six to eight times its full load current during start, and the generator must hold voltage and frequency through that transient. Where crushers, large pumps or compressors are present, a transient study is required and the resulting machine is often considerably larger than the running load suggests.

Can a 50 Hz generator be converted to 60 Hz?

Many 1500 and 1800 rpm reciprocating generating sets can be converted between 50 Hz and 60 Hz, and certain aeroderivative gas turbines switch between frequencies relatively easily. Conversion is more involved for most other gas turbine platforms. Any conversion changes output rating and alternator characteristics, so the sizing calculation must be redone at the new frequency rather than carried across.

Summary: Key Takeaways from This Generator Sizing Chart

• Three phase amps equal kVA multiplied by 1000, divided by voltage multiplied by 1.732. Always use the line to line voltage.
• Work from kVA rather than kW where possible, because the kVA figure already contains the power factor assumption.
• Standard industrial sets are rated at 0.8 power factor, so 1000 kVA equals 800 kW.
• Use the 50 Hz table for 380 V, 400 V and 415 V systems across Africa, Europe, the Middle East and Asia. Use the 60 Hz table for 208 V, 240 V and 480 V systems.
• Above roughly 2 MW, consider medium voltage generation. A 2500 kVA machine draws 3,798 A at 380 V and only 131 A at 11 kV.
• A Generator Sizing Chart gives nameplate current at reference conditions only. Apply altitude and temperature derate, check motor starting transients, and account for harmonic loads before finalising any specification.

Any Generator Sizing Chart is a design starting point rather than a design conclusion. The figures above are accurate for the conditions stated, and the conditions on your site will differ. With 150+ projects across 35+ countries, 350+ engineers, ISO 9001:2015 and ISO 45001:2018 certification and 25 years of operation without a single lawsuit, USP&E is positioned to convert these figures into a specification that holds up at commissioning.

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