How Generators are Rated? [Explained]

A generator rating is a pre-defined evaluation aimed at a particular generator model by its own manufacturers. This means that they should be able to precisely predict the power outlet, the generator is capable of producing. These ratings are a powerful tool in your buying guide when you go out for generator shopping. By being aware of the ratings of a generator you can evaluate it with your own power needs and requirements and make an informed decision.

These ratings also point towards the pivotal differences between different manufacturing companies and the generators they manufacture. It is later proved how accurate these ratings are.

Certain parameters are usually published by manufacturers, these are used to determine the size of load both in kW and kVA, maximum permissible voltage, service expected of the generator, etc. One common question that arises by people is that why generator rating in KVA is presented everywhere instead of KW?

Generators are generally rated in kilo Volt Amperes (KVA), this practice is applied to almost all energy supplying equipment. The main difference between kilo volt-amperes and kilowatts is that kilowatts represent the actual power of a generator while kilo volt-amperes represent its supposed power and output.

A generator’s power factor depends on the load of the devices that are attached to it, so it is practically not possible to correctly anticipate its real power. This power is hence, always approximately calculated.

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Generator Rating Calculation:

The full load current of a generator is calculated in this way: I= 1000 x S / V . Now S represents the generator rating in kilo volt-amperes and V equals the generator rated voltage in Volt.

Not knowing how to calculate in kilovolt amperes can be really frustrating sometimes, with our generator rating formula, this problem can be solved for you.

Different capacity generators have different calculations from Watts to Amperes. For example, a 3000-watt generator, its allowable load power is 0.8 the current, then, can be calculated as

I = 3000 / (120 x 0.8) = 31.25 A (Amperes)

Learn more about Best 5000 Watt Generators

KVA Rating chart:

Creating a cut sheet information is normally comprised of kW, KVA, Frequency, Voltage, and phase of the generators. Granted, this is the standard requirement of any project, yet it is not the only thing that determines its exact size. For further parameters that would facilitate engineers to determine the load size precisely, major manufacture companies now provide different Apps that prove really helpful in this regard. For more general information a generator rating chart is provided below.

There is a standard rule of generator power output calculation. Nearly all companies rate the generator output in Watts or kilowatts. Now the general formula for this is watts = Volts x Amps. For example, if you purchase a 5 kW generator, the output it provides will be 41.67 amps.

KVA Rating to Amperage Conversion Chart 80% POWER FACTOR


kV•A	kW	208V	220V	240V	380V	440V	480V	600V	2400V	3300V	4160V
6.3	5	17.5	16.5	15.2	9.6	8.3	7.6	6.1
9.4	7.5	26.1	24.7	22.6	14.3	12.3	11.3	9.1
12.5	10	34.7	33	30.1	19.2	16.6	15.1	12
18.7	15	52	49.5	45	28.8	24.9	22.5	18
25	20	69.5	66	60.2	38.4	33.2	30.1	24	6	4.4	3.5
31.3	25	87	82.5	75.5	48	41.5	37.8	30	7.5	5.5	4.4
37.5	30	104	99	90.3	57.6	49.8	45.2	36	9.1	6.6	5.2
50	40	139	132	120	77	66.5	60	48	12.1	8.8	7
62.5	50	173	165	152	96	83	76	61	15.1	10.9	8.7
75	60	208	198	181	115	99.5	91	72	18.1	13.1	10.5
93.8	75	261	247	226	143	123	113	90	22.6	16.4	13
100	80	278	264	240	154	133	120	96	24.1	17.6	13.9
125	100	347	330	301	192	166	150	120	30	21.8	17.5
156	125	433	413	375	240	208	188	150	38	27.3	22
187	150	520	495	450	288	249	225	180	45	33	26
219	175	608	577	527	335	289	264	211	53	38	31
250	200	694	660	601	384	332	301	241	60	44	35
312	250	866	825	751	480	415	376	300	75	55	43
375	300	1040	990	903	576	498	451	361	90	66	52
438	650	1220	1155	1053	672	581	527	422	105	77	61
500	400	1390	1320	1203	770	665	602	481	120	88	69
625	500	1735	1650	1504	960	830	752	602	150	109	87
750	600	2080	1980	1803	1150	996	902	721	180	131	104
875	700	2430	2310	2104	1344	1274	1052	842	210	153	121
1000	800	2780	2640	2405	1540	1330	1203	962	241	176	139
1125	900	3120	2970	2709	1730	1495	1354	1082	271	197	156
1250	1000	3470	3300	3009	1920	1660	1504	1202	301	218	174
1563	1250	4350	4130	3740	2400	2080	1885	1503	376	273	218
1875	1500	5205	4950	4520	2880	2490	2260	1805	452	327	261
2188	1750			5280	3350	2890	2640	2106	528	380	304
2500	2000			6020	3840	3320	3015	2405	602	436	348
2812	2250			6780	4320	3735	3400	2710	678	491	392
3125	2500			7520	4800	4160	3740	3005	752	546	435
3750	3000			9040	5760	4980	4525	3610	904	654	522
4375	6500			10550	6700	5780	5285	4220	1055	760	610
5000	4000			12040	7680	6640	6035	4810	1204	872	695

Generator rated Voltage:

A generator’s Voltage rating is usually described as the operating voltage between two of its 3 terminals meaning it is the phase to phase voltage. Small or medium-sized generators’ rated voltage is generally one of a list of standard voltages whereas for large generators it is selected at a level fitted for fiscal and efficient generator design. The rated voltages range is more or less:

4000 to 14000 V for small generators
12000 to 2000 V for medium generators
14000 to 28000 V for large generators

Read about Best Inverter Generator for Camping

Standby Generator Ratings:

The home standby generators are usually more expensive and their installation is also expensive as they are not like normal generators to be installed by just about anyone, rather an experienced electrician is required to install them properly, hence the labor cost of that should also be considered in the total cost of a standby generator.

Certain elements are a must to understand while choosing the right ratings.

The average load factor
Will the generator be running independently or alongside a utility
The maximum required load
The approximate hours per year that the generator will be running

These generators usually provide more power and tend to provide electricity for almost all the appliances of a standard household. One more feature is that these generators mostly come with an automatic switch and can start automatically when the power goes out. The best feature (arguably) is the one that runs a self-diagnosis every once in a while and it informs you promptly if maintenance is needed. Their range is approximately 5000 to 20000 watts.

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Scott

I'm an engineer with 9 years of experience working on generators and inverters. Love writing about different gadgets and really passionate about energy and it's applications