FAQs

Got questions about generators, hire, compliance or servicing? Find quick answers below, organised by topic.

Can I run two generators in parallel to cover a larger load

Yes. Paralleling combines output for a larger load, provides N+1 redundancy, and enables load-dependent switching — shutting down units when not needed to avoid light running. It requires synchronising controllers, motorised circuit breakers and correct protection settings. iPower designs and commissions parallel generator systems of all scales.

How much spare capacity should I build in

For most standby applications, 20–25% headroom above your calculated peak running load is appropriate. This covers load growth, future additions and avoids the engine running at 100% continuously (which accelerates wear). Life safety specifications often mandate minimum headroom percentages.

What is sub-transient reactance (Xd'') and why does it...

Sub-transient reactance is a property of the alternator that determines how much voltage dips when a sudden load is applied. A lower Xd'' means better voltage maintenance under sudden load steps — a 'stiffer' electrical source. This matters most for large motor starts, UPS loads and block-applied loads. For life safety and critical applications, specify Xd'' ≤12%. Standard commercial alternators can be 15–25%. iPower specifies the appropriate alternator for your load type.

What effect does a UPS have on generator sizing

UPS systems present a non-linear load with harmonic distortion (from the rectifier input stage), which stresses the alternator and can cause overheating. For UPS loads, upsize the generator by 1.25–1.5× the UPS kVA input rating and specify a low sub-transient reactance (Xd'') alternator. Always obtain the UPS input power factor and THDi from the UPS manufacturer before sizing.

How do I size a generator for motors and compressors

Motors draw 5–7 times their full-load running current at the moment of starting (direct-on-line). This causes a momentary voltage dip on the generator. As a rule of thumb, no single direct-on-line motor should represent more than 20–30% of the generator's standby kVA rating. Soft starters and VFDs dramatically reduce starting current, often allowing a smaller generator. iPower models motor starting scenarios on request.

What is wet stacking and how do I avoid it

Wet stacking occurs when a generator runs at very low load (typically below 30% of rated output) for extended periods. Unburned fuel and carbon accumulate in the exhaust. It reduces efficiency, can damage the engine and produces a thick black smoke event when load is eventually applied. Prevent it by: correct sizing (don't massively oversize), running the generator under load regularly, and carrying out periodic load bank testing.

What is the difference between standby, prime and...

Standby (ESP): Maximum output during a mains failure — not for continuous use. Typically 10% above prime. Prime (PRP): Continuous power, unlimited hours, with 10% overload available for 1 hour in 12. Continuous (COP): Constant load, unlimited hours, no overload — for off-grid or prime mover applications. For a building that only uses the generator when mains fails, standby rating is appropriate. If the generator is the sole power source, prime or continuous rating applies.

What is derating and does it affect generator output

Generator manufacturers rate output at standard conditions (typically 25°C, sea level). In hot climates, high altitudes or poorly ventilated plant rooms, output falls. As a guide: approximately 1% per 100 metres above sea level, and approximately 1% per 5.5°C above rated ambient. iPower accounts for derating in every specification we produce.

How do I size a generator for my building or site

The correct process: -

List every load that will run simultaneously (not just installed capacity)
Note the kW and power factor of each load
Calculate total kVA = sum of (kW ÷ power factor) for each load -
Add 20–25% spare capacity margin
Check for large motor starting requirements (motors demand 3–7× running current on start) -
Specify the appropriate load acceptance class (G1–G4) for your application Our engineering team can carry out a full load assessment. Don't guess — oversizing wastes money, undersizing causes problems.

Our engineering team can carry out a full load assessment. Don't guess — oversizing wastes money, undersizing causes problems.

What is power factor and why does it matter

Power factor (PF) is a number between 0 and 1 describing how efficiently a load uses electrical current. A PF of 1.0 means all current is doing useful work (resistive loads like heaters). A PF of 0.8 means only 80% is useful — the rest circulates as reactive current. Motors, transformers and fluorescent lighting typically have PF of 0.7–0.85. A generator must supply all current regardless, so a motor-heavy site may need a larger generator in kVA terms than the raw kW figure suggests.

What does kVA mean and how is it different from kW

kVA (kilovolt-amperes) is apparent power — the total electrical demand a generator must supply. kW (kilowatts) is real power — the actual useful work done. The relationship is: kW = kVA × power factor. Most diesel generators are rated at 0.8 power factor, so a 100 kVA generator delivers 80 kW of real power. When sizing, you need to consider both the kVA demand and the power factor of your loads.