Determine your facility's exact electrical load profile. Add your equipment, account for motor starting surges, and find the perfect generator capacity to avoid overloading and system failure.
For 3-phase systems, ensure your single-phase loads are distributed evenly across L1, L2, and L3. An unbalanced load can cause the generator to trip even if the total kVA is below the rated limit.
Calculating the electrical load of your facility is the first and most critical step in securing a reliable power backup solution. At PowerProKe Ltd, we have seen countless businesses suffer from avoidable downtime simply because their generator load profile was incorrectly estimated. This guide provides the technical framework needed to accurately profile your power requirements.
A generator is not just a "box of power." It is a sophisticated engine-alternator set that must respond dynamically to the electrical demands of your building. If you underestimate your load, you risk overloading the unit, which leads to circuit breaker trips, voltage drops, and potential damage to the alternator windings.
Conversely, overestimating your load leads to inefficient fuel usage and the dreaded "wet stacking" condition, where unburnt fuel accumulates in the exhaust due to the engine running too cold. Accurate sizing ensures your generator operates in its "sweet spot"—typically between 50% and 80% of its rated capacity.
To calculate your load, you must understand the relationship between Amps, Volts, Watts, and Power Factor. Depending on whether your system is single-phase or three-phase, the formulas differ slightly.
A hotel in Mombasa has a running load of 120kW. However, it has 4 large laundry dryers and a swimming pool pump system.
The Calculation:
Hospitals must account for "Life Safety" loads which have zero tolerance for voltage dips.
If the ICU and Operating Theatres draw 80kW, and the HVAC draws 100kW, the generator must be sized to handle the 100kW motor start while maintaining perfect voltage for the 80kW critical electronics. This often requires a generator with a high-performance AVR (Automatic Voltage Regulator).
Factories with heavy machinery must use the Locked Rotor Amps (LRA)value for calculations.
A 50HP motor might only draw 40kW while running, but it can draw over 200kW for the first 2 seconds of starting. If the generator is only 150kVA, it will stall immediately.
Any equipment with an electric motor (A/C, pumps, elevators, compressors) requires 3 to 6 times its running current to start. This is the single most common cause of generator sizing errors.
Continuous loads are those that run for more than 3 hours. Intermittent loads (like a microwave or a small water pump) only run occasionally. We size the generator based on the maximum possible simultaneous load.
Inductive loads (motors, transformers) cause the current to lag behind the voltage. This inefficiency is represented by the Power Factor. A lower PF means you need a larger generator (more kVA) to provide the same amount of useful work (kW).
Failing to account for the LRA (Locked Rotor Amps) of industrial motors leads to immediate system failure upon startup.
Sizing a generator for 100% of today's load leaves no room for growth. We recommend a 20-25% safety margin for future equipment.
Putting all single-phase loads on one leg of a three-phase generator causes overheating and premature alternator failure.
Nameplates often show average consumption, not peak. Always use peak values for critical sizing calculations.
While our calculator provides a high-accuracy estimate, it cannot replace a physical site load study. Our engineers use Power Quality Analyzersto log your actual consumption over 24-48 hours, identifying hidden peaks and harmonic issues.
If you are planning a new generator installationor experiencing frequent trips, our team provides professional generator diagnosticsto ensure your system is perfectly matched to your load.
Don't guess your power needs. Let PowerProKe Ltd perform a technical site audit and provide a guaranteed power solution for your business.
List every piece of equipment, multiply its quantity by its wattage, and apply a surge factor for motors. Sum these values and divide by your power factor (usually 0.8) to get the required kVA.
kW (Kilowatts) is the "Real Power" that does work. kVA (Kilovolt-Amperes) is the "Apparent Power" which includes reactive power. Generators are rated in kVA because the alternator must handle the total current, even the inefficient reactive part.
This depends entirely on the equipment. A typical office building might need 50-100kVA, while a data center or hospital of the same size could require 500kVA or more due to cooling and critical systems.
Two smaller generators in parallel (N+1 redundancy) offer better reliability and fuel efficiency at low loads, but are more expensive to install than a single large unit.
Explore more engineering resources in our Tools & Calculators section, including fuel consumption and maintenance schedule tools.