FAQs

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

Does load acceptance class affect the physical size of...

Not directly in terms of kVA rating, but higher-class generators often have larger alternators (for low Xd''), more sophisticated governors and AVRs. This can increase physical size, weight and cost compared to an equivalent kVA unit in a lower class.

Which load acceptance class is required for hospital...

Hospital generator specifications typically require G3 as a minimum for essential services and life safety circuits. This reflects the mix of sensitive clinical loads — theatre equipment, monitoring systems, imaging equipment — that cannot tolerate significant disturbance. For specialist clinical environments, G4 may be derived and specified.

How does a soft starter or VFD affect generator load...

Soft starters and VFDs reduce motor starting current dramatically — from 6× inrush to perhaps 1.5–3× — reducing voltage dip and potentially allowing a smaller generator or lower class. However, VFDs introduce harmonic distortion (5th and 7th harmonics) that can cause alternator heating and voltage distortion. Both factors must be considered in the full generator specification.

What happens if I specify the wrong load acceptance class

Under-specifying causes real problems. VFDs, PLCs and sensitive medical devices may fault or trip when the generator struggles under a large load step — meaning your critical systems go offline at exactly the moment you need them. Over-specifying wastes money. iPower advises on the appropriate class for your specific load mix.

In plain English, what does transient load acceptance...

When a generator is running and you suddenly switch on a large load, the generator momentarily struggles to keep up. Voltage dips and frequency drops for a fraction of a second until the engine and controls catch up. How far they dip and how quickly they recover is what load acceptance class measures. A G1 generator might dip 25% in voltage for a second. A G3 generator might dip 10% for 200 milliseconds. The less tolerant your loads are of that dip, the higher the class you need.

What is a Class G4 generator and what is it suitable for

G4 is a special applications class where the voltage and frequency performance requirements are not defined by the standard itself, but are instead agreed between the user and the generator manufacturer for the specific application. It exists for situations that fall outside the defined parameters of G1–G3 — for example, highly specialist medical equipment, certain telecoms or defence applications. If your project requires G4, you need to define exactly what transient performance you need and specify it contractually with your generator supplier.

What is a Class G3 generator and what is it suitable for

G3 imposes significantly tighter transient limits. Required when the load includes thyristor-controlled equipment, frequency-sensitive drives, sensitive process controls or telecoms equipment. Most hospital and data centre specifications call for G3 as a minimum. Achieving G3 typically requires a more capable engine governor, a faster-responding AVR and often a lower Xd'' alternator.

What is a Class G2 generator and what is it suitable for

G2 sets tighter limits than G1. Appropriate for general commercial and light industrial use — offices, retail, general manufacturing with standard motors and controls. Most mid-market commercial generator sets sold for standby duty are G2 class.

What is a Class G1 generator and what is it suitable for

G1 is the most basic standard. Suitable for loads tolerant of relatively wide voltage and frequency variations — simple heaters, basic lighting, non-critical water pumps. G1 generators are the most widely available and cheapest to specify, but are not appropriate for sensitive electronics, critical motors or life safety applications.

What are generator load acceptance classes

ISO 8528-5 defines four performance classes (G1–G4) describing how well a generator maintains voltage and frequency when a sudden load is applied or removed. The class dictates the maximum permissible voltage and frequency deviations during a transient event. Higher class = tighter (more demanding) specification.