Generator Maintenance Checklist

The reason load testing sits at the top of this document is that it is the only part of a generator service that tests the thing the generator is for. Everything else on the page tests the machine: the oil is clean, the coolant is correct, the belts are sound, the battery holds charge, the alternator insulation is good. All of that is necessary and none of it answers the question the building is actually asking, which is whether this set will pick up the load when the mains fails and hold it for as long as it takes. An off-load weekly run, which is what most sets get, demonstrates that the engine starts and runs. That is worth having and it is a small fraction of the claim being made. A diesel engine run lightly loaded for long periods does not simply fail to prove itself; it actively deteriorates, because unburnt fuel and soot accumulate in the cylinders, the exhaust and the turbocharger, which is wet stacking, and a set that has been exercised off load for five years can be in materially worse condition than one that was left alone. The second thing worth copying is that the changeover is timed step by step rather than recorded as a pass. The useful number is not that the set started but how many seconds elapsed between the mains failing and the load being carried, because that figure has to be read against something: the ride-through of the uninterruptible supplies, the tolerance of the control systems, the restart behavior of the chillers. A set that accepts load in eight seconds and a set that takes forty both pass a test that only asks whether the transfer happened.

This is close to a model service: tested to full load on a bank, a changeover comfortably inside its requirement, and fuel stock above the stated autonomy. Sixty two checks were completed across the engine, the fuel system, the alternator and the installation, plus the eight load tests and the ten timed transfer steps, and almost all of them passed. The single defect is a battery bank with a low cell voltage and a charger float voltage out of range, and it is graded Critical, which is the correct grading and the part worth dwelling on. Nothing about that set is going to fail while it is running. It will fail to start, which on a standby machine is the same outcome and arrives with no warning at all, because the panel will show the charger working right up to the morning the engine will not turn over. Batteries cause more standby generator failures than engines do, which is why the template asks for the charger output and the float voltage as measurements rather than accepting the indication on the panel. Critical on this document has a specific meaning: the building currently has no backup power, and that is a conversation to have today rather than at the next review. The fixed distribution this set feeds has its own document, the electrical maintenance checklist, and the planned intervals both sit inside a PPM schedule alongside the equipment maintenance checklist that covers the rest of the site's machinery.

The uncomfortable part of this comparison is that the cheap test is not merely less informative than the expensive one, it is actively harmful if it is the only test the set ever gets. A diesel engine is designed to run under load. Run it at a small fraction of its rating for ten minutes a week, year after year, and fuel that does not fully burn accumulates as soot and unburnt diesel in the cylinders, past the rings, into the exhaust and through the turbocharger. That is wet stacking, and its symptoms are exactly what a nervous operator does not want: a set that smokes heavily, loses power and may not reach its rating when it is finally asked to. So a building that has diligently exercised its generator every Monday morning for five years can be in worse condition than one that has left it alone, and the weekly run is the thing that hid the problem, because it ran every time. The resolution is not to stop exercising the set but to load it properly on a schedule, which usually means a load bank, which usually means a line item somebody has to approve. That is the real reason full load tests are rare, and it is why this document reports the maximum load actually tested to as a headline figure rather than burying it: it makes the gap between what was paid for and what was proved visible to the person who signs the contract. The fixed distribution downstream of the set has its own regime in the electrical maintenance checklist, and a test that requires taking the building off supply belongs in a plant shutdown checklist.