In short. Small temporary loads still need the correct voltage, enough starting capacity and a safe connection. A portable or low-kVA rental set is chosen by phase, running kW, the single hardest starting load, cable length and whether the load contains sensitive electronics, not by picking the cheapest machine that is roughly big enough. Low kVA does not mean low consequence; a 5 kVA set wired without an earth is as dangerous as a 500 kVA one.
What “small” covers and why the class is loose
Small is a navigation class, not a fixed rating. In practice it covers portable petrol sets of a few kVA, single-phase diesel sets and three-phase sets up to roughly 30 kVA, used for site offices, water pumps, power tools, temporary lighting, refrigeration, exhibition stalls and backup for clinics or shops. What the class has in common is that one or two loads usually decide the selection, and that the installation is often done by people who are not electricians. Where the requirement outgrows this band, the medium generator rental page picks up where motor sequencing starts to dominate.
Seven questions before a small set is allocated
- Single-phase or three-phase? Most small tools, lights and domestic refrigeration are 230 V single-phase; submersible pumps and small machines above about 3 kW are often 415 V three-phase.
- What is the running kW, with everything that will actually be on at once?
- What is the largest motor, and does it start direct-on-line?
- How long is the cable from the generator to the load?
- Will the set run outdoors, under cover or indoors, and how is exhaust handled?
- How many hours a day, and for how many days?
- Is there sensitive electronic equipment such as laptops, medical devices, audio or inverters?
The answers map directly to a rating, a phase arrangement, a cable size and a position.
One difficult starting load can dominate
A 1.5 kW submersible pump looks trivial next to a 10 kVA set until it starts. A direct-on-line induction motor draws around six times its rated current for a fraction of a second, and a small alternator sags under that surge, so the lights dim and electronics reset. The generator must be sized for the start, not the run. The motor starting guide covers the full method; the quick check is below.
Starting kVA = motor kW x locked-rotor multiple / (efficiency x running power factor)
Motor kW is the nameplate output, the locked-rotor multiple is typically 6 to 7 for a standard induction motor started direct-on-line, and efficiency and running power factor are taken from the motor data or assumed conservatively. As an illustration (illustrative), a 2.2 kW pump with a locked-rotor multiple of 6, efficiency of 0.8 and a running power factor of 0.82 demands roughly 20 kVA for a fraction of a second. No small set delivers that without a deep dip, which is why manufacturers publish a motor-starting kVA figure that allows a transient dip of 25 to 35 percent. A 10 to 12 kVA set will usually start such a pump if nothing else is running; a 5 kVA set will not. Two pumps must start one after the other, never together.
| Typical small load | Running demand | Starting behaviour | Selection note |
|---|---|---|---|
| LED site lighting, 20 fittings | Under 1 kW | Negligible | Any set; check single-phase outlet rating |
| Site office with ACs and computers | 3 to 6 kW | Compressor starts of 1 to 1.5 kW each | Stagger AC starts; 7.5 to 10 kVA single-phase |
| Submersible dewatering pump 2.2 kW | About 2.5 kVA | Six times current, DOL | 10 to 12 kVA three-phase, start pump first |
| Chest freezers and display chillers | 0.3 to 0.8 kW each | Short compressor surge | Allow 3 times running for the group |
| Audio and video for a small event | 1 to 3 kW | Low surge, sensitive to waveform | Prefer sets with good AVR; avoid shared circuits with motors |
Avoid the extension-cord mindset
The most common failure in small hires is not the generator. It is a reel of undersized flexible cable, a loose plug, no earth and no residual-current device. Even a 5 kVA installation needs overcurrent protection at the set, an earth connection, an RCD on the socket circuits, cable sized for the current and the length, and protection from rain and standing water.
Cable length is a rating problem
Small sets are often placed far from the load to reduce noise, and the long run then costs more voltage than the alternator can spare. The voltage drop guide gives the calculation; as an illustration (illustrative), 2.5 square millimetre flexible cable carrying 16 A single-phase over 50 metres drops roughly 14 to 15 V, about 6 percent of 230 V, before any motor start raises the current. Moving to 4 or 6 square millimetres, or shortening the run, is cheaper than a larger generator.
Weather and position
Portable sets are not rated for rain. During the Hyderabad monsoon a small set needs a canopy or shelter that still lets cooling air in and exhaust out. Exhaust must never discharge into a closed room, tent or stairwell; carbon monoxide has no smell and small sets are the ones most often run indoors.
Sensitive electronics and generator quality
Laptops, audio mixers, medical monitors and inverter chargers are more sensitive to voltage and frequency variation than a pump is. A small diesel set holds voltage within a few percent in steady state but dips on motor starts, and a poorly adjusted governor lets frequency wander. Keep motors on a separate circuit or set, ask for a machine with a well-maintained electronic AVR, and consider a small UPS ahead of the most sensitive equipment. Inverter-type portable sets give clean output at low load but are poor at motor starting. For stalls and shows, the event power page covers layout and noise.
Fuel and running hours for small sets
Small diesel sets typically burn between 1 and 4 litres per hour depending on size and load. A base tank on a 10 kVA set covers a shift but not a night, so define who refuels and when. A long hire at 10 percent load is harder on the engine than a short hire at 70 percent, because light running builds carbon. Duration and site planning are covered on the rental and temporary power overview and general sizing on the generator rental page.
Related photographs and videos
Common mistakes
- Sizing to the sum of the running loads and ignoring the pump start. The lights dim, the set labours and the pump trips every time it tries to start.
- Running a long, thin extension cable from a distant set. Voltage at the tools falls so far that motors overheat and electronics reset.
- Omitting the earth and the RCD because the set is small. A damaged tool cable becomes a fatal shock hazard with nothing to disconnect it.
- Running a portable set inside a tent or store room for shelter. Carbon monoxide accumulates without warning.
- Plugging audio or medical equipment into the same circuit as a compressor. Every compressor start disturbs the sensitive load.
What to send us
Tell us the list of equipment to be powered with the kW or amp rating of each, which items contain motors, whether you need single-phase or three-phase, the distance from the generator position to the load, the hours per day and number of days, and whether the set will be under cover. A photograph of the pump or machine nameplate removes most guesswork. Send it through the generator rental enquiry.
Questions engineers ask
What size generator do I need for a 1 HP water pump?
A 1 HP (0.75 kW) single-phase pump runs on about 1.3 to 1.5 kVA but draws several kVA for a moment when it starts direct-on-line. A 3 to 5 kVA set normally handles it provided nothing else heavy starts at the same time; check that the set’s published motor-starting capability covers the pump’s starting current.
Can I run a small generator indoors if I open the windows?
No. Exhaust from a small engine fills a room faster than windows can clear it, and carbon monoxide poisoning gives little warning. Place the set outdoors with the exhaust pointed away from openings and bring the cable in; if weather protection is needed, use a ventilated canopy or shelter.
Is a petrol or a diesel small set better for a hire?
Petrol portable sets are light, quiet and suited to a few kW for short periods. Diesel sets cost more per kVA but burn less fuel per kWh, tolerate long running and start motors better. For anything above a day or above about 5 kVA, diesel is usually the better choice.
Does a small rental set need an earth electrode?
Yes, unless it is connected to an installation that already has an effective earth. Drive a rod or use the site’s earth bar, bond the generator frame and neutral according to the set’s arrangement, and fit an RCD on the socket outlets so that a fault is cleared quickly.
Generators by rating
- Under 15 kVA generators
- 15–50 kVA generators
- 50–125 kVA generators
- 125–250 kVA generators
- 250–500 kVA generators
- 500–1000 kVA generators
- 1–2 MVA generators
- 2 MVA and above generators
Technical content reviewed by D. Srinivas Reddy, Managing Partner and Service Engineer, Reddy Generators. Last updated 19 October 2026.