Industrial backup generator maintenance: a complete guide

A backup generator is an insurance policy. It exists to work when everything else fails: when the grid goes down, when a storm takes out the supply or when a fault on the incoming cable leaves the business without electricity. The problem is that, like any insurance policy, you only find out whether it works when you actually need it. And if the generator refuses to start that day, the consequences can be severe.

Generator maintenance is one of the most neglected tasks in industrial facilities. A generator that is not properly maintained can fail at the critical moment, leaving essential systems without power: refrigeration, security, communications, emergency lighting or mission-critical production equipment.

This article covers the essential maintenance tasks, recommended schedules and the most common mistakes that compromise the reliability of these machines.

Types of generators and their uses

Standby (emergency) generators

These are the most common in industrial and commercial installations. They are sized to supply power to the facility’s critical loads during a grid outage. Their use is intermittent and limited to emergency situations. Under applicable regulations, they must be able to start and assume load within a maximum time (typically 10-15 seconds for safety-related loads).

Prime (continuous duty) generators

Designed to operate as the primary power source for extended periods. They are used in installations without reliable grid access or as part of a cogeneration system. They require a more intensive maintenance programme than standby units.

Peak-shaving generators

Used to reduce peak grid demand and avoid penalty charges on the electricity bill. They run during the hours of highest consumption and their use is regulated by emissions legislation.

Preventive maintenance plan

Weekly checks

Although it may seem excessive for equipment that may not start for months, weekly checks are essential:

• Fuel level: verify that the tank is at least 75% full. A generator that runs out of fuel during an emergency is an avoidable critical failure.
• Starter battery condition: check the voltage (should be above 24 V on most diesel units). Batteries are the single most frequent point of failure in backup generators.
• Control panel indicators: confirm that no alarms or fault indicators are active.
• Coolant level: check the engine coolant level.
• Engine oil level: verify with the dipstick that it is within range.
• General visual inspection: look for fuel, oil or coolant leaks, loose cables, signs of corrosion or mechanical damage.

Monthly tasks

• Start test: run the generator for at least 15-30 minutes under load. This is the most important maintenance task — and the one most frequently skipped. A generator that is not started regularly can develop starting problems due to battery deterioration, condensation in the fuel or carbon build-up on engine valves.
• Battery charger check: verify correct operation and proper float charge voltage.
• Automatic transfer switch (ATS) test: confirm that the automatic changeover works correctly, both for transfer to generator and retransfer to mains.

Quarterly tasks

• Fuel analysis: diesel stored for extended periods can degrade, accumulate water and develop biological contamination (bacteria and fungi that form a sludge clogging filters and injectors). Periodic analysis detects these problems before they compromise starting.
• Filter replacement (fuel, oil and air) based on accumulated running hours or the manufacturer’s schedule, whichever comes first.
• Inspection of cooling circuit hoses and connections: hoses deteriorate over time and can fail without warning.
• Check of anti-vibration mounts and supports.

Annual tasks

• Engine oil change: even if running hours are low. Oil degrades through oxidation and condensation over time, not just through use.
• Coolant replacement or verification of antifreeze and corrosion-inhibitor concentration.
• Full load test: simulate a real emergency by transferring critical loads to the generator for at least one hour at full rated power. This test verifies not only that the generator works but also that the electrical installation is correctly sized and that the changeover proceeds without issues.
• Alternator inspection: cleaning, insulation testing, condition of diodes and voltage regulator.
• Exhaust system inspection: condition of silencer, gaskets, fixings and thermal insulation.
• Control panel and electrical protection review.

Load testing: why it is indispensable

One of the most common reasons a backup generator fails during a real emergency is that it has never been tested under actual load. A generator can start perfectly on no load and fail when loads are connected because:

• The alternator has a fault that only manifests under load.
• The engine cannot maintain rated speed with the load connected.
• The automatic transfer switch does not operate correctly under load.
• Cables or connections have an insufficient cross-section or a poor joint that only becomes apparent when heated by the load current.

The annual load test is the only way to verify that the entire system — engine, alternator, control panel, transfer switch and cabling — functions as an integrated whole.

Common mistakes

Not starting the generator regularly

This is the most common and most serious mistake. A generator that has not been started for six months or a year has a significant probability of failing to start when needed. Batteries discharge, fuel degrades, engine seals dry out and electrical contacts oxidise.

Ignoring the batteries

Starter batteries have a service life of 3 to 5 years. Beyond that period, their cranking capacity diminishes progressively. Batteries should be replaced preventively, not when they can no longer start the engine.

Not treating stored fuel

Diesel stored in the generator’s tank degrades over time. Condensation introduces water, which encourages biological contamination. Stabiliser additives and water-separator filters are straightforward and cost-effective preventive measures.

Running tests on no load

Running the generator regularly on no load (with nothing connected) is better than not starting it at all, but it creates a problem: diesel engines that run for extended periods on no load or very light load accumulate carbon deposits in the combustion chambers and exhaust system (known as wet stacking). The recommendation is that tests should always be carried out with at least 30% of rated load.

Applicable regulations

Backup generators are governed by several regulatory frameworks. In Spain, the key references include:

• REBT, ITC-BT-28: establishes the requirement for backup or emergency power in certain public-assembly premises. Similar requirements exist in most European countries.
• RSCIEI (Industrial Fire Safety Regulation): in industrial premises at fire risk, a backup generator may be required to power fire protection systems.
• CTE DB-SI (Building Code): for non-industrial buildings, sets power-supply requirements for safety systems.
• Emissions regulations: generators are subject to emissions limits (EU Directive 2016/1628 for internal combustion engines) that affect equipment selection.

At Acoval Technical Installations we handle the maintenance of technical installations in Valencia and the surrounding area, including the inspection, testing and servicing of industrial backup generators. If you have a generator that has not been serviced in some time, or if you need to implement a rigorous maintenance programme, get in touch through our contact page.