In short. Construction-site power changes as the project moves from site establishment and excavation to structure, MEP fit-out and commissioning. Plan it as a staged load schedule rather than one generator for the whole job: identify each phase’s tools, cranes, pumps, welding and lighting, size for the largest starting event, and give the site protected distribution with earth-leakage protection. Review the arrangement whenever the layout or load changes.
Why one generator rarely fits the whole project
On a residential tower in Hyderabad or an industrial building in a Telangana estate, the first months need site cabins, lighting, dewatering pumps and a few tools. Then come tower cranes, hoists, concrete pumps and batching plant, then MEP contractors with welding and testing equipment, then commissioning of permanent services that may need stable, documented power. A set chosen for month one is too small by month six, and a set sized for the peak runs lightly loaded for most of the job. A staged plan avoids both.
Load by construction phase
| Phase | Typical loads | Planning focus |
|---|---|---|
| Site establishment | Cabins, security lighting, small tools, water pumps | Compact set, single distribution board, RCD protection |
| Excavation and foundations | Dewatering pumps, piling rig auxiliaries, lighting | Continuous pump duty, monsoon water, night lighting |
| Structure | Tower crane, hoists, concrete pump, batching plant, bar benders | Large motor starts, intermittent peaks, zone distribution |
| MEP fit-out | Welding, cutting, pressure testing, temporary lighting floors | Many single-phase loads, phase balance, harmonics |
| Commissioning | Lifts, chillers, pumps, fire systems on test | Stable voltage and frequency, records, controlled energisation |
Cranes, hoists and motor starting
Tower cranes and hoists are the hardest construction loads for a generator. Their hoist motors start under load many times an hour, and older direct-on-line or slip-ring drives draw several times their running current. Variable-frequency drives on newer cranes reduce starting current but add harmonics and may regenerate power back to the supply when lowering, which a small generator cannot absorb. Ask the crane supplier for the starting kVA and drive type, and size the set so the voltage dip stays within what the crane controls tolerate. See motor starting.
Distribution and layout
The generator position must work with tanker access, the route to the loads and the next phase of building. Cables cross haul roads, sit in excavation water and get caught by moving plant, so route them overhead or in protected crossings, label them and inspect every shift. Use a main panel at the set with outgoing feeders to zone boards, and 30 mA earth-leakage protection on every socket circuit used for hand tools and lighting. The equipment is described on temporary distribution panels and temporary power cables.
Site conditions and maintenance
Construction is hard on generators. Dust, heat and continuous running shorten service intervals. Air filters on construction sites need more frequent checks than on clean standby installations, and radiators clog with cement dust. Generators on site through the monsoon need drainage around their positions and a check of earthing after heavy rain. Plan fuel delivery and security, because unattended sites lose diesel.
Many sites now monitor rental sets remotely for running hours, load, fuel level and alarms. On a construction project this is more than a convenience: it shows when a set is oversized and could be swapped for a smaller one, flags overnight running that nobody authorised, and gives the project manager a factual basis for fuel bills. Night work needs particular care. Lighting towers and floodlights are modest loads individually, but a site lit for a night pour can draw a steady load for twelve hours, and the fuel plan must cover it.
A sizing check for the structure phase (illustrative): a tower crane with a 37 kW hoist on a drive, a 30 kW concrete pump, bar bending and cutting at 15 kW, site lighting and cabins at 25 kW. Running demand is around 110 kW, yet the crane and pump starting together with the other loads running drives the selection, and a set of about 200 to 250 kVA is a reasonable starting point to be confirmed against the crane supplier’s data.
When the grid connection arrives
Permanent supply often arrives before handover, but not always on time. If the DISCOM connection is delayed and the building needs commissioning power, the rental arrangement becomes bridging power, described on bridging power. When permanent supply is available, the temporary system is removed in a planned sequence with each zone confirmed safe.
Responsibility on a multi-contractor site
Agree who supplies, installs, operates and inspects the temporary system, who may add loads, and how faults are reported. A simple rule that nobody connects to the generator panel without the site electrical supervisor’s approval prevents most overloads and unsafe connections. Keep a log of loads added, inspections and RCD tests.
Related photographs and videos
Common mistakes
- Hiring one generator for the full project based on early loads. The crane or concrete pump phase overloads it.
- Ignoring the crane’s starting and regenerative behaviour. The generator trips on voltage dip or over-voltage when loads are lowered.
- Laying cables across haul roads without protection. Plant damages them and creates earth faults and shock risk.
- Skipping RCD testing on site boards. A failed device leaves workers with hand tools unprotected.
What to send us
Send the project programme with expected phases, the list of major equipment including crane make and drive type, concrete pump and batching plant ratings, a site plan with the proposed generator positions and access, and the expected date of permanent supply. Send a generator rental enquiry and we will propose a staged arrangement.
Questions engineers ask
What size generator does a tower crane need?
It depends on the crane’s hoist motor and drive. A crane with a direct-on-line or slip-ring hoist needs a much larger set than one with a drive. Ask the crane supplier for the starting kVA and size so the voltage dip during a hoist start stays within limits.
Is it better to have one central generator or several on site?
Several smaller sets near load zones reduce cable lengths and voltage drop and keep one fault from stopping the whole site. A central set is simpler to fuel and supervise. Large or spread-out sites usually benefit from zone sets.
Do construction generators need earthing?
Yes. The generator neutral and frame are earthed at the set, distribution boards are bonded, and earth-leakage protection relies on that earth path. Electrode resistance should be measured at installation and rechecked, particularly through dry months.
How often should a construction-site generator be serviced?
By running hours, following the manufacturer’s interval, with more frequent air filter and radiator checks in dusty conditions. Sets running two shifts reach a typical service interval within weeks.
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.