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Reviewing the Power Stuff

How Generators are Rated? [Explained]

How Generators are Rated? [Explained]

December 11, 2021 by Scott Leave a Comment

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.

Contents

  • Generator Rating Calculation:
  • KVA Rating chart:
  • KVA Rating to Amperage Conversion Chart 80% POWER FACTOR
  • Generator rated Voltage:
  • Standby Generator Ratings:

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.

  • Author
  • Recent Posts
Scott
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
Scott
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