In short. A brochure describes a product family; a datasheet defines the stated ratings and characteristics of one model under stated conditions. To rely on a generator document, match its model and revision to the equipment, check the rating basis (standby, prime or continuous), confirm the reference conditions and derate for your site. Treat figures from a similar machine, or from an undated brochure, as indicative only.
Documents are engineering evidence
Datasheets, manuals, commissioning records, wiring diagrams, test certificates and maintenance records are not paperwork for the file. They identify installed equipment, establish ratings and interfaces, support maintenance decisions and provide traceability when the system is later modified. A document is useful only when its model, revision and application actually match the equipment under review.
Know which document answers which question
| Document | What it tells you | What it cannot tell you |
|---|---|---|
| Brochure | Product family, range, typical features | Exact ratings or configuration of a specific set |
| Technical datasheet | Ratings, fuel consumption at stated loads, dimensions, weights, reference conditions | Site performance after derating, or the condition of a used set |
| Engine and alternator data | Component ratings, efficiency, reactances, temperature rise | How the set builder combined them |
| Manual | Operation, maintenance intervals, settings | Changes made on site after delivery |
| Test certificate | Results under a defined test condition | Performance under different load or ambient |
| Emission or type certificate | Compliance of the certified configuration | Compliance after unapproved modifications |
Our generator manuals page covers manuals in more detail, and the technical library explains how the document types fit together.
Start with exact equipment identity
Before relying on any technical sheet, establish the identity of the generating set, engine, alternator, controller and switchgear. Record model and serial numbers, rating, voltage, frequency, phase, duty and installation configuration. Two sets that share a family name can differ in alternator frame, cooling package, controller or emission stage. A specification from a similar machine must not be silently treated as the specification of the installed machine.
Reading a generator datasheet
Rating basis
Ratings follow the definitions in ISO 8528. Emergency standby power is for use during utility failure with limited annual hours and no sustained overload. Prime power allows unlimited hours at variable load with an average loading limit. Continuous power is for a constant load with unlimited hours. The same engine can carry three different numbers, so always confirm which one a quotation uses.
Reference conditions and derating
Ratings are stated at reference ambient temperature, altitude and humidity. At higher temperature or altitude, output falls. In Hyderabad, where summer afternoons exceed 40 °C and enclosures sit in sun, the site rating can be noticeably below the datasheet figure. Use the manufacturer’s derating curve, not a general percentage.
kW, kVA and power factor
kW = kVA × PF
Here kW is the real power the engine must produce, kVA is the apparent power the alternator must carry, and PF is the load power factor, rated at 0.8 on most industrial sets. Example (illustrative): a 250 kVA set rated at 0.8 PF delivers up to 200 kW. If the load runs at 0.9 PF, the engine reaches its kW limit before the alternator reaches its kVA limit.
Fuel consumption figures
Consumption is normally given at 25, 50, 75 and 100 percent load. These are test values under reference conditions with a stated fuel specification. Site consumption will differ with load profile, maintenance and fuel quality, so use the figures for comparison between models rather than as a guarantee.
Separate measured, stated and estimated values
Technical decisions should distinguish manufacturer data, supplier statements, engineering estimates, site observations, logged operating data and controlled measurements. Where a value is calculated or estimated, label it so, rather than presenting it as measured or certified. This matters most for fuel performance, emissions, thermal limits, fault levels and exhaust conditions. Our document and evidence status page explains the labels we use.
Public, controlled and internal documents
General technical guidance can be public. Quotation-specific datasheets, certificates and project records are shared with the customer concerned. Contracts, work orders, personal data and confidential test results remain internal unless publication is authorised. When we supply a datasheet with a quotation, it relates to the configuration quoted, and any later change to the scope should come with an updated sheet.
Common mistakes
- Comparing a standby rating from one supplier with a prime rating from another. The cheaper set appears larger but cannot carry the same continuous load.
- Using datasheet output without site derating. The set trips or overheats on hot afternoons.
- Taking brochure fuel figures as a site guarantee. Running costs exceed the budget built on them.
- Using a family datasheet for a set with a different alternator or controller. Fault levels, reactances and protection settings are wrong.
- Keeping documents without revision dates. Nobody can tell which version matches the installed equipment.
What to send us
To request a datasheet or brochure, send the make, model and rating you are considering, or for an existing set a clear nameplate photo of the generator, engine and alternator. Tell us what decision the document is for, such as sizing, installation layout or a compliance check. Use the generator sales enquiry for new equipment.
Questions engineers ask
What is the difference between standby and prime rating?
Standby rating is for emergency use during utility failure with limited annual hours. Prime rating allows unlimited hours at variable load, usually with an average loading limit. The prime figure for the same set is lower than the standby figure.
Why does my generator not deliver its datasheet output?
Datasheet ratings apply at reference conditions. High ambient temperature, altitude, poor ventilation, fuel quality and engine condition all reduce available output. Check the derating curve and the site conditions first.
Can I get a datasheet for an old generator?
Often, if the engine and alternator serial numbers are readable. For discontinued models, component datasheets may still be available even when the set builder’s document is not. Send clear nameplate photos and we will check what exists.
Are brochure fuel figures reliable?
They are reliable for the stated test conditions and useful for comparing models. They are not a guarantee of site consumption, which depends on load profile and maintenance.
Technical content reviewed by D. Srinivas Reddy, Managing Partner and Service Engineer, Reddy Generators. Last updated 19 October 2026.