| Purpose and Load Priority | Identify whether the generator will support life-safety systems, business continuity, residential equipment, industrial processes, or the entire facility. | Emergency load Standby load Optional load
Typical priority loads include fire pumps, emergency lighting, elevators, communication systems, refrigeration, servers, pumps, and medical equipment. | Separate essential and non-essential circuits before calculating the generator rating. Do not size the unit only from the total connected load. |
| Connected and Running Load | Record the rated power, operating voltage, phase, power factor, and expected operating condition of every load. | Generator output is commonly stated in kVA. The basic relationship is: kW = kVA × power factor.
A power factor of 0.8 is often used for conventional generator ratings, but the actual site load should be confirmed. | Add the running kW or kVA of the selected loads, then verify that the generator can maintain voltage and frequency under the combined load. |
| Motor Starting Requirements | List motors, compressors, pumps, fans, air conditioners, and other equipment with high starting current. | Across-the-line motor starting can create a short-duration inrush current several times higher than the running current. Soft starters and variable-frequency drives can reduce starting demand. | Check the largest motor start, the sequence of starting, and the acceptable voltage dip. A larger alternator or staged starting may be required even when the running load is moderate. |
| Required Generator Capacity | Define the minimum continuous load, maximum anticipated load, motor-starting demand, and future expansion allowance. | A planning margin of approximately 10% to 20% is commonly considered for future growth and measurement uncertainty, subject to the project engineer’s calculation. | Avoid prolonged operation below the manufacturer’s minimum recommended loading and avoid selecting a unit that is permanently operated at its maximum rating. |
| Standby or Prime Rating | Define how often the generator will operate and whether it will be used only during utility outages or as a regular power source. | Standby rating: generally intended for emergency operation during utility interruptions.
Prime rating: intended for variable-load operation where the generator is used as the main or regular power source, subject to applicable rating rules. | Use the rating category that matches the operating profile. Do not treat standby and prime ratings as interchangeable without checking the duty cycle and manufacturer documentation. |
| Voltage, Phase, and Frequency | Confirm the facility voltage, single-phase or three-phase system, frequency, neutral arrangement, and compatibility with connected equipment. | Common low-voltage systems include 220–240 V single-phase and 380–415 V three-phase at 50 Hz in many markets. Other regions commonly use 60 Hz systems. | Match the generator and automatic transfer equipment to the site electrical system. Frequency and phase cannot normally be changed by selecting a different cable size. |
| Automatic Transfer and Start Time | Define whether the system requires automatic detection of utility failure, automatic start, automatic transfer, and automatic retransfer after utility restoration. | Many emergency systems are designed for automatic start and transfer within a specified project time, often from several seconds to tens of seconds, depending on the system and local code. | Specify the required transfer time, bypass/isolation functions, manual controls, remote monitoring, and compatibility between the generator controller and transfer switch. |
| Required Runtime and Fuel Storage | State the required operating hours at a defined load, fuel type, refueling access, and fuel storage limitations. | Runtime depends on tank capacity, engine size, load percentage, ambient temperature, and fuel consumption. A runtime target such as 8, 12, 24, or 48 hours should be tied to a specific load condition. | Compare fuel consumption in L/h at 25%, 50%, 75%, and 100% load rather than relying only on the tank volume. Include fuel quality, spill containment, and local storage requirements. |
| Installation Location | Define indoor or outdoor installation, available footprint, access route, foundation, ventilation, exhaust routing, and distance from occupied areas. | Outdoor units generally require weather protection. Indoor installations require adequate combustion air, cooling-air discharge, exhaust treatment, fire protection, and safe access for maintenance. | Confirm equipment dimensions, service clearances, lifting points, cable routes, exhaust back pressure limits, and foundation loads before placing the order. |
| Ambient Conditions and Altitude | Provide minimum and maximum temperature, humidity, altitude, dust, salt exposure, and any corrosive or hazardous environmental conditions. | High altitude and high ambient temperature reduce air density and cooling performance, which can require derating or upgraded cooling equipment. Exact correction factors vary by engine and alternator. | Request a site-specific derating calculation. A unit sized for sea-level conditions may not deliver the same output at high elevation or in a hot, enclosed room. |
| Noise and Vibration | Define the maximum permitted sound level, measurement distance, operating hours, nearby buildings, and vibration-sensitive equipment. | Acoustic performance depends on engine speed, enclosure design, exhaust silencing, installation surface, and measurement method. Sound values should always state the distance and test conditions. | Consider a sound-attenuated enclosure, resilient mounts, flexible connectors, vibration isolation, and an acoustic survey where the generator is near residences, offices, or hospitals. |
| Emissions and Compliance | Identify the installation country, local air-quality rules, fuel requirements, noise limits, electrical codes, and inspection requirements. | Applicable requirements may cover engine emissions, exhaust height, fuel storage, grounding, electrical protection, fire safety, and workplace noise. Requirements vary by location and generator size. | Ask for current compliance documentation, test certificates, technical drawings, and installation requirements applicable to the project location. |
| Maintenance and Service Support | Define expected annual operating hours, service intervals, spare-parts availability, technician response time, warranty scope, and training needs. | Routine service commonly includes engine oil, oil filters, fuel filters, air filters, coolant, batteries, belts, hoses, control-system checks, and periodic load testing. Intervals depend on the engine and duty cycle. | Evaluate total ownership cost, not only purchase price. Require a maintenance schedule, recommended spare-parts list, warranty terms, and a documented commissioning procedure. |
| Testing and Commissioning | Define factory testing, site acceptance testing, load-bank testing, black-start testing, automatic transfer testing, and emergency shutdown checks. | Testing should verify voltage, frequency, phase sequence, load response, alarm functions, protection settings, fuel autonomy, transfer operation, and performance under the specified site conditions. | Include test procedures and acceptance criteria in the purchase specification. Record measured results and retain commissioning documents for future maintenance. |
| Supplier Documentation | Require a complete technical package before final approval. | Useful documents include datasheets, dimensional drawings, wiring diagrams, fuel-consumption curves, noise data, derating charts, installation manuals, maintenance schedules, certificates, and spare-parts lists. | Compare suppliers using the same technical data points and load conditions. Reject quotations that provide only a nominal kVA figure without operating limits or site assumptions. |
