In short. Rent the capacity the operation requires, not the number someone guessed. A workable generator rental is qualified by eight pieces of information, configured as a chain from generator to load, fuelled on a calculated schedule rather than a full tank, and serviced on the engine’s interval even while it is on hire. Where the consequence of a stoppage is serious, redundancy is decided before mobilisation, not after the first failure.
The eight questions that qualify a rental
Every rental enquiry we handle is reduced to the same short list before a set is allocated. It is usually answered in one phone call, yet it prevents nearly all of the mismatches that make a hire go wrong.
| Question | Why it matters | Typical answer |
|---|---|---|
| Application | Decides the duty, noise and emission constraints | Factory bridging, event, construction, commissioning |
| Location | Transport, access, ambient conditions, local DG restrictions | Site address and a pin or photograph |
| Running load | Sets the base rating | kW or kVA, or an equipment list |
| Largest starting load | Often sets the rating instead of running load | Motor, pump, compressor, transformer or UPS rating and starting method |
| Voltage, phase, frequency | Confirms the alternator connection | 415 V three-phase, 50 Hz; or 230 V single-phase |
| Duration | Fuel, service and commercial structure | Hours, days, weeks or months |
| Daily operation | Fuel schedule and service interval inside the hire | Hours per day, continuous or shift-based |
| Connection | Transfer equipment and cable scope | Existing panel, ATS, temporary board, direct to equipment |
Smaller requirements where a single difficult starting load dominates the selection are covered separately under small generator rental. For the broader planning questions of duration and site, see the rental and temporary power overview.
The rental configuration chain
The generator is the first link in a chain that ends at the load. A typical scope runs: generator, main protection at the generator outgoing terminals, cable sized for the route, temporary distribution with outgoing protection, and then the load, with a transformer or transfer equipment inserted where the site voltage or the need to switch between sources requires it. Each link is selected to suit the ones either side of it. A 630 A outgoing breaker on the set does not protect a 150 metre cable rated for 250 A, and a temporary board still needs an earth connection for its protection to work.
Interfaces are part of the rental
When rental generation supports an existing facility during planned outages or as bridging power while a permanent set is repaired, the connection must integrate with what actually exists on site. Not every load should move to the rental source; the loads that move are the ones the operating plan says must be supplied, and the generator rating and the changeover scheme are built from the same load hierarchy.
Fuel: calculate the schedule, do not trust the tank
A full base tank at mobilisation is not a fuel strategy. The question that matters is when the next delivery must arrive to protect the reserve the project needs. Consumption depends on load factor, not on the set’s rating, so a universal litres-per-hour figure is misleading.
Refuel interval (h) = (usable tank volume in litres, less the reserve) / consumption at expected load (L/h)
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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 98852 01608.
Here the usable volume is the tank capacity minus the dead volume below the suction, the reserve is the quantity the project insists on holding (often enough for one more delivery cycle), and consumption at expected load comes from the manufacturer’s curve for the specific set. As an illustration (illustrative), a 250 kVA set carrying a 150 kW average load burns somewhere in the region of 35 to 45 L/h depending on the engine; with a 500 litre base tank, 50 litres of dead volume and a 100 litre reserve, the usable 350 litres gives roughly eight to ten hours before the reserve is touched. For a plant running two shifts, that means a daily delivery or an external tank. The fuel consumption guide covers the load-factor relationship in more depth.
A lower litres-per-hour figure does not mean a more efficient set; a lightly loaded large generator burns less per hour and more per kWh than a correctly loaded smaller one. Compare litres per kWh for a long hire.
Service during the hire
A rented generator remains a maintained machine. A long project can accumulate enough running hours to cross an oil and filter interval, typically every 250 to 500 hours depending on the engine and the supplier’s maintenance basis, in the middle of production. That should be known at the planning stage, not discovered when the service-due alarm appears. Before mobilisation, a long-duration hire should define operating responsibility, the scheduled service dates and who performs them, consumables and who pays for them, the breakdown reporting pathway and response arrangement, fuel responsibility, and access for the service technician while the site is working. Actual intervals must follow the maintenance basis of the specific set supplied.
When can the set be stopped?
If production runs continuously, ask whether the required load can remain supplied while one generator is serviced. If the answer is no, that is an architecture question to settle before deployment, either by scheduling service into a planned stoppage or by renting a second set.
Redundancy: decide it before the failure
If the rental generator stops, what stops with it? For a construction site office the answer may be an afternoon’s inconvenience. For a cold store, a hospital wing or a continuous process, the consequence justifies evaluating standby generation, two smaller units in place of one, or an alternative connection to a second source. A second set parked at the gate is only redundancy if it is fuelled, connected through transfer equipment and able to take the load automatically or within a known manual switching time. Where the hire is long enough that owning would be cheaper, the rent versus buy guide sets out the comparison.
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Common mistakes
- Quoting the running load and forgetting the starting load. The set is sized correctly for steady state and trips or dips badly every time the largest motor starts.
- Treating the base tank as the fuel plan. The generator shuts down on empty, usually at night, and restarts with air in the fuel system and sludge drawn into the filters.
- Letting the service interval arrive unplanned. Production has to stop for an oil change that could have been scheduled into a known window.
- Renting a single large set for a continuous process. Any fault, however minor, stops everything, when two smaller sets would have kept part of the load alive.
- Leaving the connection method undefined until delivery day. The crew arrives to find no changeover, no earth and no space for the cable, and the hire starts a day late.
What to send us
Send the eight qualification answers above: application, site location, running load, largest starting load, voltage and phase, duration, daily hours and connection method. Add a photograph of the incoming panel or the equipment to be supplied, the cable route length, and a note on fuel responsibility and urgency. Submit them through the generator rental enquiry and we will respond with a configuration and availability status.
Questions engineers ask
Can you tell me the exact generator size immediately?
Only if the load data is complete. With running load, largest starting load and starting method, a rating can be stated with confidence in most cases. Where the load is motor-heavy, includes a transformer to energise or carries a large UPS, a short load assessment or a motor-starting check is needed before the rating is final.
What is the minimum rental period?
Short hires of a day are common for events and tests, and long hires run to months. The commercial structure changes with duration because transport and connection costs are fixed while the daily rate is not, so a one-day hire carries a higher effective daily cost than a month. State the real duration and we will quote accordingly.
Who is responsible if the generator breaks down during the hire?
The hire agreement should name the breakdown pathway, the contact, the expected response and who covers consumables and repairs. For long industrial hires we recommend writing in a scheduled inspection as well, since most mid-hire failures are preventable through routine checks of coolant, belts, batteries and fuel filters.
Does an acoustic canopy matter for a short hire?
In residential, hospital, hotel and office locations it matters on the first night. Canopied sets hold noise to the limits expected for DG sets, while open sets need a separate enclosure or a remote position. Tell us the surroundings and operating hours so the right type is allocated.
Can the rental generator run in parallel with the building supply?
Not without synchronising equipment and DISCOM agreement. Standard rental connections use a changeover or ATS that keeps the two sources separate, so the load is on one source or the other with a brief interruption at transfer. Parallel operation is a project configuration, not a standard hire.
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Technical content reviewed by D. Srinivas Reddy, Managing Partner and Service Engineer, Reddy Generators. Last updated 19 October 2026.