In short. A rental generator is one part of a temporary power system. A sound rental plan defines the load and its starting demand, the real duration including likely extensions, the cables, distribution, earthing and changeover around the set, fuel supply and reserve, and who is responsible for operation, maintenance and damage. Compare quotations only after putting them on that same scope, because a low daily rate often covers less.
Temporary does not mean improvised
The machine may be temporary; the engineering controls cannot be. A rental installation still needs a load assessment, source sizing, correctly rated cables and distribution, protection, earthing, fuel planning, safe access, commissioning and a named operator. A set dropped on a site with a borrowed cable and no earth electrode is a hazard to people and to the equipment it feeds. The service overview at rental and temporary power lists the components that make up a complete temporary system.
The common rental situations
| Situation | Typical duration | Key planning point |
|---|---|---|
| Planned DISCOM or substation shutdown | Hours to a few days | Transfer sequence and who switches back when supply returns |
| Transformer or main set failure | Days to weeks | Speed of connection to existing busbar, protection settings |
| Bridging until permanent supply is ready | Weeks to months, often extended | Fuel logistics and maintenance over a long hire |
| Construction site | Months | Changing layout, cable protection, multiple distribution points |
| Event | Hours to days | Public safety, redundancy, noise |
Planned work is covered in planned-outage power, and longer gaps in bridging power.
Sizing a rental set
Do not size a rental set from the facility’s total installed load. Size it from the loads that will actually run during the hire, then check the largest motor start and any large load step. A shutdown that keeps only lighting, IT and one chiller may need a third of the site’s normal demand. Equally, a contractor’s tower crane or a batching plant can need a set much larger than its running kW suggests because of starting current. If the end load is uncertain, a modular arrangement of two or three smaller sets can be run in proportion to demand.
Fuel planning
Runtime (h) = usable tank volume (L) / consumption at expected load (L/h)
Diesel generator calculator
Fuel use, runtime, tank size and cost
How this is calculated
Real power is kVA × power factor. Fuel use is estimated as L/h ≈ 0.04 × rated kW + 0.22 × load kW, which follows the usual shape of modern diesel gensets: about 0.26 L per kWh near full load, rising towards 0.38 L per kWh at a quarter load because the engine's fixed losses are spread over less output.
If you enter the full-load figure from your engine datasheet, the curve is scaled to match it. Runtime is usable fuel ÷ L/h. Tank size is L/h × hours, plus the reserve margin, divided by the usable fraction.
These are planning estimates, typically within 10 to 15 percent of a healthy engine. Actual use depends on the engine model, its condition, altitude, ambient temperature and how the load varies. For a figure you can rely on, use the manufacturer's fuel curve or a metered test.
Estimates only, worked out in your browser. For a checked selection, send us your load list and site details or call 098852 01608.
Usable volume is the tank capacity less the unusable bottom reserve, and consumption is taken from the manufacturer’s curve at the expected load, not at full load. Worked example (illustrative): a 250 kVA rental set carrying about 150 kW may burn around 40 L/h. With 900 L usable in its base tank, runtime is about 22 hours. For continuous operation that means daily refuelling, so the plan needs a delivery schedule, a reserve that is never used for planning and, for long hires, an external tank with level indication. See rental capacity and runtime planning.
Connection, protection and earthing
A theoretically suitable busbar is not a practical connection point if temporary cables cannot be brought to it safely. Plan the cable route, its protection from vehicles and its length, since voltage drop rises with distance. When a site moves from DISCOM transformer to generator supply, the available fault current falls, so breakers that cleared faults quickly on the grid may react slowly on the set; protection settings need checking. The rental set needs its own neutral and body earthing arrangement consistent with the site system. Where switching between grid and rental supply is involved, an interlocked changeover or ATS prevents back-feeding the DISCOM network.
Comparing quotations
Check what is in the hire charge and what is extra: transport both ways, installation and removal, cables and distribution boards, fuel, operator, routine service during the hire, breakdown replacement, insurance and damage liability, and the minimum hire period. A lower headline rate may exclude several of these. Agree in advance the terms for extension, early return and additional capacity, because projects change, and confirm availability for the actual dates and location rather than relying on a general list.
Running the hire well
For longer or critical hires, agree how run hours, fuel received and consumed, kW readings, alarms and inspections will be recorded and who responds to an exception. Recording load and energy alongside fuel allows a meaningful efficiency check; if a set is persistently below 30 percent load, a smaller set or fewer modules may serve better and cut fuel. Keep maintenance access clear as the site changes, and re-check cable routes when work areas move. Define what happens when the permanent source returns, including who switches and in what order.
Common mistakes
- Hiring by connected load; the set runs at light load for weeks and fuel cost per kWh doubles.
- Forgetting the largest motor start; the set trips when the chiller or crusher starts.
- Leaving fuel responsibility vague; the set runs dry overnight and the critical load drops.
- Connecting without an interlocked changeover; the rental set back-feeds the DISCOM line when supply returns.
- Comparing day rates without scope; the cheaper quote adds cables, transport and operator charges later.
What to send us
Send the site location, start date and expected duration, the loads that must run with the largest motor rating, the voltage and phase, daily operating hours, where the connection will be made and photographs of the access route and connection point. Send your generator rental enquiry and we will confirm a complete scope.
Questions engineers ask
How quickly can a rental generator be connected?
It depends on size, location, access and how ready the connection point is. A site with a prepared changeover and cable route can be connected far faster than one needing a new termination. Confirm timing for your site at enquiry.
Who refuels a rental generator?
Either party, as agreed in writing. The plan should name who orders fuel, who checks levels and what reserve triggers a delivery.
Is rental cheaper than buying?
For short or uncertain needs, usually. For permanent needs with regular running, ownership usually wins. The comparison must use the real duration and full scope, not the day rate alone.
Does a rental set need earthing on site?
Yes. The neutral and frame must be earthed consistently with the site system, with electrodes tested before energising.
Wondering what a hire costs? See how generator rental is priced in Hyderabad — day, week and month structure, operator, transport and fuel.
We serve all of Telangana and Andhra Pradesh and every district within about 300 km of Hyderabad, with project support across India. See the areas we serve.
Technical content reviewed by Srinivas Reddy, Managing Partner, Reddy Generators. Last updated 19 October 2026.