Guide
Generator service intervals: what the law says, and what it does not
Updated
People look for a legal number here and there is none. That is useful, because it tells you where the real obligation sits.
What the law actually requires
A standby generator is work equipment. Under the Provision and Use of Work Equipment Regulations 1998 you must keep it in an efficient state, in efficient working order and in good repair.
Where a machine has a maintenance log, the log must be kept up to date (HSE, PUWER overview). Nothing in PUWER names a service interval for a generator.
On inspection, HSE says the need for inspection and its frequency should be set by risk assessment. That takes account of the manufacturer's recommendations and the conditions the equipment faces (HSE, inspection of work equipment).
So how often does the law say to service a generator? It says maintain it, and expects you to justify the frequency you chose.
Where your actual schedule comes from
- The manufacturer's schedule
- Engine and alternator manufacturers publish schedules in running hours, usually with a calendar backstop for sets that run very little. For a standby set that runs a handful of hours a year, the calendar backstop is what governs.
- How the set is used
- Prime power and regularly loaded sets reach hours milestones quickly. Standby sets accumulate almost no hours but suffer from standing: fuel ageing, battery decay, condensation, seized components.
- What the set protects
- Life safety systems, critical process and data loads justify more frequent proving than a set backing up a warehouse light circuit. This is the risk assessment HSE is asking you to be able to show.
- Environmental conditions
- Coastal, dusty, very cold or containerised installations deteriorate faster than a clean indoor plant room, and HSE expects that to shorten inspection intervals.
A defensible regime for a standby set
- Routine running checks at the frequency the risk assessment supports, with the results recorded rather than remembered. Many critical sites run a brief no-load or building-load start weekly or monthly.
- Planned service to the engine manufacturer's schedule, on hours or the calendar backstop, whichever falls first.
- Periodic proving under load, because starting is not the same as carrying the load. See load bank testing.
- Fuel condition monitoring, because stored diesel is a consumable with a shelf life, not a permanent asset.
- A maintenance log kept up to date, which is both a PUWER expectation and the only evidence you will have when someone asks why the set failed.
Beware anyone quoting a statutory generator service interval. There is none in PUWER. Where fixed intervals appear, they come from a manufacturer's schedule, an insurer's requirement, a sector standard or a contract. It is worth knowing which of those you are actually complying with.