Application

Diesel Generators for Construction Sites

A construction site generator is the only power source on site for months at a time, which makes it a prime power machine rather than a standby one. It runs ten to sixteen hours a day in dust and heat, carries welders and dewatering pumps, and moves to a different corner of the site when the work front changes. The duty rating is the first decision, and it is the one most often got wrong.

Sets for construction are normally quoted between 100 kVA and 300 kVA, most often as canopy or containerised units, and increasingly as trailer mounted sets that follow the work.

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Requirements

What a construction site specification has to state

Typical site power requirements. Local site rules and the equipment list govern.
Item Typical requirement Why it changes the set
Duty rating Prime power (ISO 8528-1 PRP), not standby A prime-rated set is a different machine from the standby set of the same kVA, and the fuel curve changes with it
Running hours 10-16 h per day, and often six days a week, for the life of the project Service intervals are set in hours, so the schedule has to fit the site
Load list Dewatering pumps, tower crane, hoists, welding sets, concrete plant, site offices The largest motor start and the welder load usually decide the rating
Load variation Load changes hourly as fronts open and close A lightly loaded set runs inefficiently and can wet-stack; the sizing has to suit the real average, not the peak alone
Harmonic loads Welding sets and inverters draw non-linear current The alternator may need oversizing for the same kW
Dust and heat Ambient above 45 °C in summer, with airborne sand and cement dust Filters, radiators and service intervals all change; a canopy keeps the worst off the machine
Noise Site noise limits at the nearest residential boundary, often with different day and night figures Decides between a standard and an acoustic canopy
Mobility The set moves as the work front moves Decides between a trailer chassis, a skid and a container
Fuel and security Bunded storage on site, with theft protection and a documented refuelling procedure Fuel is the largest running cost and the most commonly stolen item on a site
Changeover Direct connection to a site distribution board, or a changeover for a temporary supply alongside a utility connection Decides the output arrangement and the protection fitted to the set

Configurations

Configurations we quote most often

Common site arrangements. Each rating links to its power range page.
Rating per set Typical arrangement Fits Range page
100 kVA / 80 kW One set, canopy or trailer mounted Villa and small building sites, dewatering and site offices 100 kVA
200 kVA / 160 kW One set, plus a second for the later stages Mid-size projects with a tower crane and hoists 200 kVA
300 kVA / 240 kW One set as the site supply, or two in parallel Multi-block sites, infrastructure and plant-heavy works 300 kVA
400 kVA / 320 kW and above Two sets with load sharing Large infrastructure works and camps with permanent utilities 400 kVA

Reference configuration

A worked example

This is an illustrative configuration, not a delivered project. It shows how the requirement table above turns into a specification. Replace the figures with your own load list before pricing.

Example: a mid-size building site with a tower crane, dewatering and a site office block.
Parameter Example value
Dewatering Two pumps at 22 kW, one running continuously and one on level control
Tower crane and hoists About 45 kW of motor load, started in sequence
Welding and small plant Two welding sets at 12 kVA each plus cutting and compaction equipment
Site offices and welfare About 30 kW of air conditioning, lighting and water heating
Realistic average load About 110 kW, peaking at about 150 kW
Rating selected One set at 200 kVA / 160 kW, prime power rating, in an acoustic canopy
Duty Prime power, 12 h per day, six days a week
Fuel Base tank plus a bunded on-site storage tank refuelled weekly
Mobility Trailer mounted for the first phase, landed on a plinth for the main works
Service interval Shortened from the standard interval because of dust loading, with filter checks weekly

Questions

Questions we are asked about site sets

Should a site generator be rated prime power or standby?

Prime power, for anything that runs as the main supply. Standby and prime ratings are different declarations of the same hardware: prime power is the continuous rating with a defined overload allowance, and standby is the higher figure that applies to mains-failure duty only. Running continuously at a standby rating is outside the declaration, and it usually shows up as premature engine wear rather than an immediate failure.

Why does the set use more fuel per kWh on a site than expected?

Because a site load varies and the set is often lightly loaded. Efficiency falls away below about 50-60% load, so a set that averages 30% load can use noticeably more fuel per kWh delivered than the datasheet curve suggests. Where the average load is low, a smaller set with a second unit for peak periods is usually cheaper to run than one large machine.

How often does a site set need servicing?

The engine manufacturer’s interval is expressed in running hours, commonly in the 250-500 h band, and on a dusty site it is normal to shorten it and to check the air filter far more often than the schedule says. At 12 h a day, a 500 h interval arrives in about six weeks, so the service has to be planned into the programme rather than booked when the set complains.

Can a site set run with a utility supply as well?

Yes, with a proper changeover arrangement. The common pattern is a temporary utility supply for base load with the generator as the primary source, switched through a changeover device so the two can never be connected together. Where the generator is the only source, it is connected straight to the site distribution board with its own protection, and the earthing arrangement is documented on the panel.

How do you control fuel theft and fuel quality on a site?

Lockable filler caps, a tank that can be locked or isolated, fuel level monitoring with an alarm, and a written refuelling procedure with a log. On quality, the risks are water and dirt rather than the fuel itself, so a bunded tank with a water trap and periodic checks of the filter bowl covers most of it. Biofuel blends need particular attention where a set stands for weeks without running.

Related

Related applications and ranges

Powering a site?

Send the equipment list, the daily running hours and the site noise limit. Prime power duty changes the rating, so start there.

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