Site office power is easy to under-size because cabins are added one at a time. A rental generator must carry air conditioners, computers, lights and a water pump without tripping. Matching the set to the real load and the cable run keeps the office productive.
Quick Answer
Add up every load in the cabin before choosing a generator size.
Allow for air conditioner starting current, which can be 3 times the running load.
Keep the generator at least 30 metres from offices where noise matters.
Use a properly sized cable and a changeover switch, not extension leads.
A 10 kVA set usually covers one cabin with a small air conditioner.
What is site office?
A site office generator is a temporary power set rented to run cabins, containers and site facilities during a construction or remote project.
It means a mobile, self-contained supply that is installed, fuelled and serviced by the rental company.
site office in practice
Typical cabin loads and the set that suits them:
| Site setup | Connected load | Generator size |
|---|---|---|
| One cabin with lights and fan | 3 kVA | 10 kVA |
| Two cabins with air conditioning | 8 kVA | 15 kVA |
| Four cabins and a small lab | 15 kVA | 25 kVA |
| Six cabins with computers | 22 kVA | 40 kVA |
| Office plus workshop | 35 kVA | 60 kVA |
| Camp with canteen and laundry | 50 kVA | 80 kVA |
What does a site office generator rental cost in Nigeria?
A 10 kVA rental generator costs about 60,000 to 90,000 naira per day in Lagos.
A 25 kVA set runs about 100,000 to 150,000 naira per day.
A 60 kVA set costs about 180,000 to 280,000 naira per day.
Monthly contracts usually reduce the daily rate by 15 to 25 percent.
Fuel is charged separately and depends on load and running hours.
Delivery, cable and a changeover switch add 80,000 to 250,000 naira.
How is site office carried out?
- List every appliance and its running and starting current.
- Add a 20 percent margin for future cabins and small tools.
- Choose a set with enough capacity at the site altitude and temperature.
- Plan a level, ventilated position away from windows and walkways.
- Install a changeover switch, earth the set and protect the cable run.
- Commission, brief the site team and record the fuel and hour readings.
Sources
Manufacturer generator sizing guides, NIS 1000 electrical installation rules, IEC 60364 temporary installation guidance, Rental fleet operating data
Build the load list first
Walk through every cabin and write down each load. Include lights, fans, air conditioners, computers, printers, a water pump and phone chargers.
Add the running watts, then add the starting surge for motors. An air conditioner can draw 3 times its running current for a few seconds.
A 20 percent margin covers the extra cabin or tool that always appears after the contract starts.
Why air conditioners decide the size
In a Nigerian site office, cooling is usually the largest load. Two split units can easily draw more than all the lights and computers combined.
Check the unit rating plate, not the marketing name. A 1.5 horsepower unit may draw 1.2 kW running and 3.5 kW at start.
If the set is sized only for running load, the breaker trips every time the compressor restarts. Stagger the start times or fit soft starters.
Noise, position and exhaust
Keep the set away from cabin windows and air intakes. Noise travels further than most site managers expect.
Point the exhaust away from the office and never into a closed area. Carbon monoxide kills quietly.
Use a soundproof canopy where the site is near homes, schools or a hospital. The extra rental cost is usually cheaper than a complaint.
Cable runs and distribution
Use a cable rated for the full load and the run length. Voltage drop on a long thin cable causes dim lights and overheated motors.
Run cables overhead or in a protected trench. A cable lying in a traffic route will be cut within days.
Fit a small distribution board with an RCD and labelled circuits. Extension leads daisy-chained across a site are a fire risk.
Fuel and servicing during the rental
Agree who supplies fuel before mobilisation. On most contracts the client pays for fuel and the rental company supplies the set and servicing.
Record the hour meter at delivery and at every refuel. Fuel consumption claims are impossible to settle without a log.
The rental company should service the set at the manufacturer interval. Keep the service sheet with the site records.
Demobilisation and damage
Inspect the set at collection and photograph any existing damage. Do the same at return.
Clean the canopy and remove fuel before transport. A full tank is a handling and spill risk.
Settle the final invoice against the hour meter and the signed delivery note.
Related guides from this series
- Generator Rental for Construction Site
- Generator Rental for Coworking Spaces in Lagos
- Generator Rental Packages in Lagos, Monthly, Weekly and Ad Hoc Pricing
About the author
Illuminate Engineering Limited supplies rental generators and temporary power to construction and commercial sites across Nigeria.
Frequently Asked Questions
What size generator does a site office need?
A single cabin with a small air conditioner usually needs 10 kVA. Four cabins with cooling and computers need about 25 kVA.
Can I run a site office from an extension lead?
No. Use a fixed cable, a distribution board and an earth connection. Extension leads are not rated for continuous site loads.
Who pays for fuel on a generator rental?
It varies by contract. Most Nigerian rentals charge the client for fuel and include servicing in the rental rate.
How far should the generator be from the cabin?
At least 30 metres where noise and exhaust matter. Use a soundproof set if the site is tight.
Conclusion
A site office generator is a small plant with a real load profile. Count the loads, allow for starting surge and plan the cable run.
Get the size right and the office stays cool, connected and quiet through the whole project.