Guide 08 Building operation and maintenance
What is the right maintenance schedule for a standby DG set?
A standby diesel generator set is maintained on two overlapping clocks: daily or weekly checks by whoever is on site, and periodic servicing by running hours or calendar time, whichever comes first. Skipping the monthly load run is the single most common cause of a genset that starts but will not carry load.
- Topic
- Building operation and maintenance
- Checked
- 23 September 2026
- Sources
- 3
- Questions
- 5
01
Daily, weekly and periodic checks
Daily or weekly attention covers fluid levels, visible leaks, battery condition and the state of the controller, the kind of walk-round check that catches a problem before it becomes a breakdown. These are quick, do not need the set to run, and belong in a logbook that a contract auditor or a fire officer can ask to see.
Periodic service work, oil, filters and coolant changes, belt and hose inspection, exhaust and electrical connection checks, follows the engine maker's schedule expressed in running hours and calendar time together, whichever limit is reached first. A genset that has sat idle for a year still needs its calendar-based service even if it has barely run.
- Fluid levels and visible leaks
- Battery condition and terminal connections
- Controller status and any active alarm
- Logbook entry for the day or week
02
Exercising the set on load
A standby generator that never runs under load is not being maintained, it is being stored. Industry guidance is to exercise it at least once a month, for at least thirty minutes, at no less than one-third of its nameplate rating. Running keeps parts lubricated, works oxidation off electrical contacts and burns through fuel before it degrades in the tank.
Where the building's own load is not available for the exercise run, a load bank of at least one-third of the set's rating is used instead of letting it run unloaded. Battery electrolyte is worth checking on the same rhythm, at least every 200 running hours, since a flat or sulphated battery is the most common reason a genset fails to start on demand.
03
Wet stacking, and why light running causes it
Wet stacking is the build-up of unburned fuel and soot inside the exhaust system of a diesel generator that spends long periods running at light or no load. The cylinders never reach the temperature needed for complete combustion, and the residue shows up as oily black smoke and a sooty exhaust stack. It is a symptom of how the set is run, not a manufacturing fault.
The fix is in the exercise schedule rather than in a repair: keep no-load running to a minimum, and when the set does run, load it to a meaningful fraction of its rating rather than idling it. A set that wet-stacks repeatedly is worth checking for an exercise routine that is too light, before any component is blamed.
04
Noise and emissions rules for a new set
A new diesel generator set up to 1000 kVA, manufactured on or after 1 January 2005, must not exceed 75 dB(A) measured at one metre from the enclosure surface under Central Pollution Control Board rules, and the acoustic enclosure has to be fitted at the manufacturing stage, not added on site afterwards. Larger sets are managed through room acoustic treatment sized to the required insertion loss.
Emissions are a separate, newer requirement. CPCB IV+ is the current genset engine emission standard for sets up to 800 kW, notified in November 2022 and applying to new sets sold from 1 July 2023, tightening the limits on nitrogen oxides, hydrocarbons, carbon monoxide and particulate matter. A set already installed and certified to an earlier norm can generally keep running under the norm it was certified to.
Asked next
Questions people also ask
What is the right maintenance schedule for a standby DG set?
How often should a standby DG set be run on load?
At least once a month, for at least thirty minutes, at no less than one-third of the set's nameplate rating, using the building load or a load bank if the building load is not available. This keeps parts lubricated, prevents electrical contacts from oxidising and uses fuel before it degrades in the tank, and it is the single check most often skipped.
What is wet stacking in a diesel generator?
Wet stacking is unburned fuel and soot accumulating in the exhaust system of a diesel generator run for long periods at light or no load, because the cylinders never reach combustion temperature. It shows as oily black smoke and residue at the exhaust stack, and the remedy is to minimise unloaded running and exercise the set at meaningful load, not to treat it as a fault.
How often should DG set battery electrolyte be checked?
Industry guidance from generator manufacturers puts battery electrolyte checks at least every 200 running hours, alongside the monthly load-run schedule. A flat or sulphated starting battery is one of the most common reasons a standby set fails to start on demand, so this check sits alongside fluid, filter and connection checks rather than being left to the annual service.
What noise limit applies to a new DG set in India?
Under Central Pollution Control Board rules, a diesel generator set up to 1000 kVA manufactured on or after 1 January 2005 must not exceed 75 dB(A) measured at one metre from the enclosure surface, with the acoustic enclosure fitted at the manufacturing stage. Larger sets are managed through room acoustic treatment sized to the required insertion loss rather than a fixed decibel figure.
What is CPCB IV+ and does it apply to an existing DG set?
CPCB IV+ is India's current emission standard for diesel genset engines up to 800 kW, notified on 3 November 2022 and applicable to new sets sold from 1 July 2023, tightening limits on NOx, hydrocarbons, carbon monoxide and particulate matter. A set already installed and certified to an earlier CPCB norm can generally continue running under the norm it was certified to.
Checked against
Sources
- 01Power Topic 7004, Maintenance is One Key to Diesel Generator Set Reliability, Cummins Power Generation
- 02Noise limits for diesel generator sets, Central Pollution Control Board
- 03Genset emission notifications, CPCB IV+, Central Pollution Control Board
This guide explains how the system works in general, as the documents above describe it, and was last checked on 23 September 2026. Rules and thresholds change: the governing document is the authority, not this page.
On this site
Where this meets the work
Have a requirement rather than a question?
Send the specification, the part or the drawing. The first reply says what we can do and what we need from you.