How Do I Size A Standby Generator Correctly?

Choosing the right Standby Generator starts with understanding your business's electrical requirements, which equipment needs backup power, and how long it may need to operate during a mains power failure.

Correct sizing helps ensure the generator can support the required loads reliably without burdening you with unnecessary capital costs or fuel consumption.

How do you calculate what size generator you need?

The first step is to identify the equipment and essential systems that must remain operational during an outage. This could include IT equipment, UPS systems, production machinery, refrigeration, lighting, security systems, and building services.

Assess the electrical demand of these loads. However, simply adding together the rated power may not provide an accurate result, as the equipment does not always operate at capacity at the same time. In addition, motor-driven equipment can also draw significantly higher starting currents than during normal operation.

Generator sizing must account for maximum demand, starting currents, load changes, power factor, and the generator's ability to respond to sudden increases in demand.

Where a UPS is installed, its input characteristics and battery recharging requirements should also be considered.

What information is needed to size a generator?

To recommend a suitable generator, a supplier will typically need to understand:

Electrical loads: which equipment needs backup power, including its power ratings and operating requirements.
Maximum demand: the expected total electrical demand when the equipment is operating.
Starting requirements: whether motors, pumps, compressors or other machinery create significant starting currents.
Backup requirements: whether the generator must power the entire site or only essential equipment, and how long backup power is required.
Electrical infrastructure: the existing supply, distribution equipment, transfer arrangements and any UPS systems.
Installation conditions: the available space, ventilation, exhaust arrangements, noise restrictions and fuel options.
Future requirements: planned expansion, additional equipment and any need for redundancy.

How do you choose the right generator for your business?

The final specification should reflect the site's actual operating requirements, the consequences of losing power, and the conditions under which the generator will operate.

Generator capacity is commonly expressed in kilowatts (kW) and kilovolt-amperes (kVA), so it is important to understand both the real power demand and the required apparent power.

For larger or more complex installations, a professional load assessment is recommended. This helps establish the appropriate generator rating, identify any required infrastructure changes, and ensure that the generator can operate reliably with all the connected equipment.

The aim is to specify a generator that meets your business's power requirements, allows for appropriate future needs, and delivers dependable backup without unnecessary oversizing or expense.

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