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Generator School · 05

What is a load bank — and why every standby unit needs one

A load bank is a portable resistive load — basically a big bank of heating elements wired to a generator's output. When connected, the load bank draws current at a precise percentage of the generator's rated capacity (25 %, 50 %, 75 %, 100 %). The whole point is to exercise the engine and alternator at real working loads, in a controlled environment.

01

Why standby units need load banking

A backup generator typically runs unloaded for 10 minutes a week as part of its automatic test cycle. The engine warms up, but never produces real torque. Over months and years, this causes 'wet stacking' — unburnt diesel and soot coat the exhaust valves, turbocharger, and exhaust system. Power output drops and the engine eventually fouls. The cure is to run the unit at 100% load for 60 minutes annually. The high exhaust temperature burns off the deposits and re-seasons the engine.
02

What we measure

During a load-bank test, our technician records: • Voltage at every load step (must stay within ±2 % of nominal) • Frequency stability (must stay within ±0.5 Hz) • Exhaust gas temperature • Coolant temperature trend • Oil pressure under load • Vibration at the alternator bearings We then issue a printed certificate showing the unit successfully held the rated load — required by some insurance underwriters for critical-facility cover.
03

How often

Annually for standby duty. Twice yearly for hospitals, telco huts, and data-centre prime backup. Capital Power Systems maintenance plan customers get this included.
Quick answers

FAQs

Don't see your question? Call 07 5529 0351 or contact us.

Sometimes — but most buildings can't draw 100 % of the generator's rated load on demand. A 250 kVA standby unit feeding a small office that draws only 60 kVA can never be tested above 24 % real load. A load bank fills the gap.
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