In short. Rental planning answers four questions: how much power, for how long, how it connects, and who supplies fuel and support. Size from measured or listed load, allow for starting and growth, plan the connection point and protection, and agree fuel and attendance before the unit arrives.
Step 1: Define the duty
- Planned outage, shutdown, event, construction or emergency backup.
- Duration, hours per day and whether the load is steady or variable.
- Voltage, phases, frequency and whether the site has an existing changeover point.
Step 2: Size the capacity
Use the same logic as permanent sizing: running load, largest motor start, power factor, derating and a modest margin. See capacity requirement. Rental fleets come in standard sizes, so choose the next size up, or two smaller units in parallel for resilience.
Step 3: Runtime and fuel
Example (illustrative): a 250 kVA set at about 40 L/h running 10 hours a day for 6 days uses about 2,400 litres. Decide whether fuel is delivered by tanker, stored in a rental tank or topped up daily. See fuel tank and runtime.
Step 4: Connection
| Method | Notes |
|---|---|
| Prepared inlet or connection point | Fastest and safest; install in advance |
| Temporary cabling to a distribution board | Needs isolation, correct cable rating and protection |
| Through a rental ATS or changeover panel | Prevents back-feeding the utility |
| Parallel with utility | Only with approval and synchronising |
See rental ATS, cables and distribution panels. Never connect a generator to a building supply without proper changeover; back-feeding can kill utility workers.
Step 5: Site readiness
- Space, access for delivery, level ground and ventilation.
- Exhaust direction and noise limits.
- Earthing of the generator and neutral arrangement.
- Fire safety and spill containment.
- Permits and utility notifications.
Step 6: Support
Decide whether an operator is on site, how alarms reach you, and the response time for faults. Agree who monitors fuel levels and who performs refuelling.
Worked example (illustrative)
A factory shutdown needs 180 kW running with a 45 kW motor started DOL for eight days, two shifts. Starting check suggests a 300 kVA set. Fuel at about 45 L/h for 16 hours a day is about 5,760 litres over eight days, so a rental tank and a delivery schedule are planned. A changeover panel is arranged at the main board. The plan covers load, runtime, fuel, connection and support before delivery, so nothing is discovered on the day.
Planning a rental
A rental generator provides power for events, shutdowns, construction or emergencies. The right size and runtime plan avoid shortfalls and waste.
| Step | Detail |
|---|---|
| 1. Load | Total running kW and kVA, largest motor start |
| 2. Duty | Hours per day, days, continuous or standby |
| 3. Size | Prime rating match; 70 to 80 percent loading target |
| 4. Redundancy | Spare set for critical use |
| 5. Connection | Cable size and length, breaker, earthing, change-over arrangement |
| 6. Fuel | Tank size, refuelling plan |
| 7. Site | Placement, ventilation, noise, safety, access |
Worked example (illustrative)
A plant shutdown needs 280 kW running with a 55 kW motor starting by star-delta. Select a 400 kVA prime rated set: 280 kW ÷ 0.8 = 350 kVA running, loading about 85 percent of 400 kVA. For margin choose 500 kVA. Duration 6 days, 12 hours per day at 220 kW average: fuel about 72 hours × 60 L/h ≈ 4,300 litres, requiring a refill plan.
Connection safety
- Use a proper changeover or isolated connection point, never a backfeed through a plug.
- Confirm earthing arrangement and RCD or earth-fault protection.
- Fence and label the unit, and brief the operators.
See rental power and sizing guide.
Common mistakes
- Choosing a size from the nameplate of the equipment, not the real load.
- No plan for fuel delivery.
- Temporary cables undersized or unprotected.
- No changeover arrangement.
What to send us
Send the load, dates, location and connection details. Send your application details. See also rental and temporary power.
Questions engineers ask
How do I choose rental generator size?
From the running load, the largest start, power factor and a margin, then the next standard size.
Can a rental generator connect to my building directly?
Only through a proper changeover or approved arrangement. Direct back-feeding is dangerous.
Who supplies fuel?
It varies by arrangement. Agree it in advance, with delivery schedule and responsibility for monitoring levels.
Do I need two smaller units?
For critical use, two units give redundancy and may be better than a single large one.
Figures are illustrative. Rental terms and technical arrangements are confirmed per project.