Generator Load Testing: What Facility Managers Need to Know

A standby generator has one job: to carry the building when the mains fail. For a hospital, aged-care home, data room or commercial facility, that moment is exactly the wrong time to discover a fault. Regular load testing is how you know — rather than hope — the set will perform. Here’s what facility managers need to understand.

Starting isn’t the same as performing

A generator that fires up happily at no load can still fail when real demand is applied. Starting proves the battery, starter and basic fuel system work. It says nothing about whether the engine, alternator, cooling and controls can take on full load and hold stable voltage and frequency for hours. Only testing under load proves that — and under load is exactly how the set will be used in an outage.

Wet stacking: the hidden cost of running light

Diesel engines are built to run under meaningful load. Run a diesel genset at light load for long periods — as happens when a set is oversized for the building, or only ever “exercised” at no load — and unburned fuel and soot accumulate in the combustion chambers and exhaust. This condition, known as wet stacking, shows up as oily deposits around the exhaust and, left unchecked, fouls injectors and the turbocharger and steadily degrades performance. The remedy is to run the engine under proper load so it reaches temperature and burns the residue off — which is one of the things a load bank test does.

What a load bank test actually does

A load bank applies a controlled, stable electrical load to the generator without relying on the building’s own load. A resistive load bank exercises the engine; a reactive (or combined) bank also loads the alternator the way real motor and UPS loads would. During the test, a technician confirms that the set can:

• start, pick up load and ramp to its rated output;
• hold voltage and frequency stable under sustained load;
• run at proper temperature without wet stacking;
• keep oil pressure, coolant and exhaust temperatures within range.

Readings are logged throughout, giving you documented proof of capacity rather than an assumption.

How often should you test?

Practice varies by facility and jurisdiction, but the widely referenced benchmark is NFPA 110, the international standard for emergency and standby power. It calls for regular exercise — typically monthly — under a meaningful load (reaching a minimum load level or exhaust temperature), plus a full load bank test at least annually for critical (Level 1) systems such as those in healthcare. Many facilities run a brief exercise weekly and reserve the load bank test for an annual or scheduled interval.

In Australia, your specific obligations may also sit under standards for your facility type and under your insurer’s requirements — essential electrical supplies in hospitals and diesel-driven fire-pump sets, for example, carry their own maintenance regimes. It’s worth confirming exactly what applies to your site rather than assuming the generic monthly-plus-annual rhythm is enough.

The risks of skipping it

• Failure under real load — the set starts but can’t sustain the building, and you find out during the outage.
• Wet stacking damage — chronic light-load running fouls the engine and shortens its life.
• Fuel problems — stored diesel oxidises and can grow microbial contamination (“diesel bug”) that clogs filters; a load test consumes and turns over fuel.
• Undetected faults — cooling, fuel-delivery and voltage-regulation problems often reveal themselves only under load.

Each of these is cheap to catch on a scheduled test and expensive to discover in an emergency.

Perth Rewind Industries services, repairs and tests generators for commercial and industrial clients across Perth and WA, backed by an on-site workshop for motors, alternators and controls. See our generator repairs page, browse generator spares, or contact us to arrange a test or service for your standby set.