Mobile range
Trailer Mounted Diesel Generators
A trailer mounted diesel generator is a canopy set bolted to a road chassis with axles, brakes, lights and a coupling, so that the same machine can power a site this month and a different one next month. It is the standard answer for rental fleets, construction sites, events and emergency response, and the engineering question is not the generator — it is what the local road rules allow you to tow.
This page covers the trailer side: axle and brake choices by weight, what has to be on the chassis, and what has to be done on site before the set is energised.
Configurations
Trailer arrangements by weight and rating
Everything on a towing vehicle is limited by plated mass, not by the generator rating. The table below works from the trailer class back to the set, which is the order the decision has to be made in.
| Trailer class | Braking | Typical set rating | Towing |
|---|---|---|---|
| Single axle, up to 750 kg gross | Unbraked | About 20-30 kVA in a light canopy | Any car or light van with a suitable tow bar |
| Single or twin axle, up to 3 500 kg gross | Overrun (mechanical) brakes | About 60-150 kVA | Light commercial vehicle; tow bar and mirror rules apply |
| Twin or triple axle, 4 000-10 000 kg gross | Air or hydraulic brakes, breakaway system | About 150-500 kVA | Medium truck; in most countries a specific licence class |
| Low-bed or semi-trailer | Full truck braking system | Above 500 kVA | Heavy tractor unit; becomes a transport project rather than a tow |
Weight is easy to underestimate. A 200 kVA canopy set with a full base tank is typically 2.5-3.0 t, and the trailer itself adds 400-800 kg before fuel, cable drums and tooling. Weigh the finished unit rather than the catalogue figure: an overloaded trailer is a legal problem and a safety problem at the same time.
Chassis
What has to be on the trailer
| Item | Typical execution | Why it matters |
|---|---|---|
| Chassis | Welded steel channel or RHS, hot-dip galvanised or epoxy coated, with a single or double drawbar | Carries the set, the fuel and the dynamic loads of towing, not just the static weight |
| Axles | Rated per axle with a stated tyre load index; leaf spring or rubber suspension | Axle rating must exceed the plated mass, with margin for the fuel load |
| Brakes | Overrun with a breakaway cable up to 3 500 kg; air or hydraulic above that | Braking class is what sets the legal towing limit |
| Coupling | 50 mm ball for light trailers; 40 mm ring eye or a drawbar eye for truck towing | Must match the towing vehicle, and the height must suit the drawbar |
| Lighting | Two-function or multi-function lamps with side markers and a rear fog lamp where required | Lighting is the most common inspection failure on a mobile set |
| Tyres and wheels | Load-rated tyres, spare wheel on a carrier, wheel chocks stowed on the trailer | A spare is not optional on a remote site; chocks are required before any work |
| Support | Jockey wheel for unhitched handling, corner steadies or hydraulic legs for levelling | A set on suspension rocks; the base frame and exhaust must be levelled and stable |
| Fuel | Base tank inside the canopy, bunded; filling point and vent arranged away from the exhaust | Fuel and hot exhaust in the same small enclosure is the risk to design out |
| Earthing provision | Earthing stud and a stowed earth spike with cable | A mobile set has no building earth; the site connection has to be made deliberately |
| Canopy | Lockable acoustic canopy, weatherproof, with lifting eyes or forklift pockets | The set is usually lifted off the trailer for long stays, then put back for the next move |
On site
Getting output out of the set
| Item | Typical choice | Note |
|---|---|---|
| Output arrangement | CEE sockets at 16, 32, 63 or 125 A, or a hard-wired terminal box with a moulded case breaker | Sockets suit rental and short stays; a terminal box suits a fixed site |
| Protection | MCCB on the outgoing supply, plus 30 mA residual current protection on socket outlets | Residual current protection is expected wherever portable equipment is plugged in |
| Distribution | On-board distribution board, or a separate site distribution unit fed by a cable drum | A cable drum on the trailer keeps the set self-contained |
| Earthing | Earth spike driven at the set, bonded to the frame stud; neutral arrangement stated on the panel | The neutral decision affects protection settings and must be documented on site |
| Positioning | Level hardstanding, wheel chocks fitted, handbrake on, exhaust pointing away from openings | Soft ground under an axle is a common cause of a canopy that will not close |
| Noise | 70-80 dB(A) at 7 m from a standard canopy; lower with an acoustic build | Night limits in residential areas are usually the binding constraint on a temporary site |
| Fuel handling | Refuelling with the engine stopped, drip tray under the fill point, no smoking area marked | Mobile sets are refuelled from cans more often than fixed ones |
Choosing
Trailer, skid or container
| Question | Trailer mounted | Skid mounted | Containerized |
|---|---|---|---|
| Movement between sites | Tow it, if the trailer is plated for the weight | Requires a flat-bed trailer and a crane each time | Requires a low-bed or a flat rack and a crane or reach stacker |
| Set-up time on arrival | Minutes: chock, earth, connect, start | Hours: offload, position, anchor, connect | Hours to a day: lift, land, anchor, connect |
| Noise at 7 m | 70-80 dB(A) from a standard canopy | 78-96 dB(A) unless housed | 68-78 dB(A) when lined |
| Weather protection | Canopy only; the trailer frame is exposed | None unless it is housed | Best: sealed and locked |
| Security | Lockable canopy, but the unit itself can be towed away | Depends on the room | Locks and, if needed, can be stacked among other containers |
| Long-term installation | Possible, but the tyres age and the trailer occupies a footprint | Normal choice for permanent duty | Normal choice for permanent outdoor duty |
| Typical use | Rental fleets, construction, events, standby for temporary works | Plant rooms, basements, replacement of an existing set | Telecom, oil and gas, mining, remote sites, export projects |
For a site that will keep the set for more than about a year, the trailer is usually lifted off and the set is landed on a plinth, with the trailer stored. Towing a set on and off a site repeatedly wears the canopy mountings and the trailer brakes faster than the generator wears out.
Questions
Questions we are asked about trailer sets
How big a generator can go on a trailer?
Up to about 150 kVA on a trailer that stays within a 3 500 kg gross limit, and 300-500 kVA on an air-braked chassis towed by a truck. Above that the weight needs a low-bed trailer or a semi-trailer, and the unit stops being a trailer mounted generator and becomes a transport project.
Can I tow a generator trailer with a normal car?
Only within the lightest class. An unbraked trailer is normally limited to 750 kg gross in Europe, which covers a set of roughly 20-30 kVA with fuel. Anything larger needs overrun brakes and a towing vehicle rated for the plated mass — and the towing vehicle limit is often lower than the trailer limit, so check the vehicle plate, not just the trailer.
Does the trailer need its own registration or plate?
It depends on the country, and the rules are enforced at borders as well as on the road. In many markets a road-going trailer needs its own plate, lighting that meets the vehicle lighting standard, and a periodic inspection. For an export order, tell us where the unit will be registered and we will build to that requirement rather than assume.
How do I earth a mobile generator?
Drive an earth spike at the set and bond it to the earthing stud on the frame, then confirm the neutral arrangement stated on the control panel. Where the set supplies a building installation through a changeover device, the earthing is handled by that installation. Where it supplies portable equipment through sockets, the protection is on the set itself, which is why residual current protection on the outlets matters.
Can the set run while it is on the trailer?
Yes, and that is normal for short and medium stays, provided the trailer is level, the wheels are chocked, the handbrake is applied and the canopy doors are secured open against the wind. For stays of more than a few months, lifting the set off the trailer and landing it on a plinth is better for the trailer, the tyres and the noise level.
Related
Other form factors and ranges
-
Diesel generator sets
How ratings, form factors and control options are defined.
-
Silent sets
How the dB(A) figure is produced and what it costs in space.
-
Open frame sets
Skid-mounted machines for plant rooms and acoustic houses.
-
Construction sites
Prime power duty, dust, dewatering and site noise limits.
-
200 kVA class
160 kW, a common trailer rating for rental and site work.
-
Request a quote
Tell us where the unit will be registered and how it will be towed, and we size the chassis.
Buying a mobile set?
Send the rating, the country of registration and the towing vehicle. Trailer class, braking and lighting all follow from those three answers.