What size towable generator do I need for a construction site?

Add the running load of everything on at once, then add the starting surge of the largest motor. Most small crews land between 20 and 60 kW; sites with HVAC, cranes or large pumps move past 100 kW quickly.

Who refuels a towable diesel generator?

It depends on the contract. Some providers include scheduled fuel service, others deliver full and bill you for the fill on return. Ask which applies before the unit arrives.

20 - 150 kW · Diesel, with a base tank

Towable diesel generator rental

A towable genset is a diesel engine, alternator, control panel and fuel tank on a trailer. It is built for continuous duty measured in weeks, not an afternoon.

Where this category fits

Best uses

Construction sites running several trades over weeks or months
Planned facility shutdowns and temporary capacity
Continuous heavy load where fuel service can reach the unit

Poor-fit uses

Indoor or enclosed placement, and sites with strict emissions limits
Very light loads over long periods, where extended low-load running causes engine problems
Locations a trailer and a fuel truck cannot physically reach

Typical power range

Roughly 20 to 150 kW on a trailer, with larger skid and containerised sets beyond that. The right unit depends on your concurrent load and largest motor, not on the headline rating alone.

Why diesel dominates job sites

Diesel engines tolerate long runs at high load, the base tank holds enough fuel for a full shift or several, and the output range covers everything from a small crew to a tower crane.

Fuel burn scales with load. As a rough planning figure, a diesel genset consumes in the region of 0.07 gallons per kW per hour at around three-quarter load — use it to size a tank and a refuelling schedule, then confirm the real figure for the model you are quoted.

Getting it onto the site

Check three numbers before delivery day: the trailer's gross weight against the tow vehicle rating, the gate or lane width, and the ground conditions where it will sit. Soft ground after rain has stranded more units than any mechanical fault.

Also confirm where a fuel truck can reach it, and whether the placement blocks anything on a busy site.

Distribution is a separate conversation

The genset produces power at a set voltage and phase; getting it to the tools takes cable, spider boxes, transformers and sometimes a distribution panel. These are usually priced as separate line items.

Confirm voltage, phase and connection type in the quote. A 480 V three-phase unit is useless on a site expecting 120/240 V single-phase without a transformer.

Fuel, runtime and refuelling

A base tank normally covers a shift or several. As a planning figure only, diesel burn runs near 0.07 gallons per kW per hour at about three-quarter load — confirm the real rate for the quoted model.

Decide early who refuels: scheduled provider fuel service, a fuel truck you arrange, or delivered-full-returned-full billing.

Sustained running far below rated load can cause wet stacking. If your load is light, say so and let the provider size down.

Noise and emissions

Most rental units are in a sound-attenuated enclosure, but urban and night-work limits are still commonly the deciding constraint.

Ask which emissions tier the engine meets — some jurisdictions and some owners' sites require a specific tier.

Portability, towing and placement

Confirm trailer gross weight against the tow vehicle rating, gate and lane widths, overhead clearances and turning space.

Ground conditions strand more units than mechanical faults. Firm, level standing with airflow and exhaust clearance, and a route a fuel truck can still use in week three.

Spill containment and a spill kit are required in many jurisdictions — check who supplies them.

Delivery, setup, cable and grounding

Ask these before the unit is scheduled. Each one changes either the price or whether the job works at all.

Who tows and positions the unit?: Provider delivery and self-tow carry different insurance and licence requirements.
What cable, spider boxes and transformers are included?: Distribution is priced separately on most quotes and is the most commonly forgotten item.
Who makes the electrical connection?: The delivery driver almost never connects to your equipment; that is licensed electrical work.
Who supplies grounding rods and performs the ground test?: Temporary systems still need a compliant grounding arrangement.
What is the service response time, including after hours?: A long job needs a defined callout, not a best-effort promise.

What to tell the rental provider

Concurrent running load and the largest motor with its starting method
Voltage, phase and connection type your temporary panel expects
Rental window, expected hours per day and any shift pattern
Access route, gate width and ground conditions
Distance to the load, so cable can be sized and quoted
Noise limits, permitted working hours and any emissions tier requirement

Towable diesel generators at a glance
Output	Typical site	Common voltage	Planning note
20 - 45 kW	Small crew, trailers, lighting	120/240 V 1-phase	Often paired with light towers
45 - 100 kW	Mixed tools, pumps, small chillers	120/208 V 3-phase	Check motor starting loads
100 - 150 kW	Larger sites, HVAC, cranes	277/480 V 3-phase	Transformer likely needed

Confirm tow rating, gate width and ground conditions before delivery
Ask for the fuel policy: who fills, who refills, how it is billed
Match voltage and phase to the tools on site
Plan a spill kit and containment where the local rules require it

Don’t

Assume the delivery driver will connect anything electrical
Place it where a fuel truck cannot reach
Ignore night-time noise limits on urban sites
Run at a small fraction of rated load for weeks without asking about wet stacking

Common rental mistakes

Ordering by kW alone
Give the load list and largest motor and let the provider verify the rating.
Forgetting cable and distribution
Ask for a quote that includes cable, boxes and any transformer.
Placing the unit where a fuel truck cannot reach later
Plan placement against the site programme, not just week one.
Assuming voltage matches
Confirm 208 V versus 480 V and phase before delivery day.

Carbon monoxide and safe placement

Never run a generator indoors, in a garage, basement, crawl space, tent, trailer or under a covered porch — even with doors and windows open. Exhaust is invisible, odourless and can be fatal within minutes.
Place the unit outdoors on level ground, well away from doors, windows, vents and air intakes, with exhaust directed away from any occupied space. Follow the distance stated in the equipment manual.
Fit a working, battery-backed carbon monoxide alarm in any building or vehicle being powered.
Never plug a generator into a wall outlet or wire it into a building panel. Backfeeding can kill you, your household and utility crews. Any connection to building wiring requires a licensed electrician and a proper transfer device.
Shut the engine down and let it cool before refuelling, and keep fuel away from hot surfaces.

This is educational guidance, not a substitute for the equipment manual, your rental specialist or a licensed professional.

Common questions

Sizing power for a job site?

Send your concurrent load, largest motor and site access details. We route it to providers who carry towable diesel in your area.

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