What Size Generator Do I Need for a Construction Site?
Most tradies need a 5kVA to 8kVA construction site generator, enough for a saw, a compressor and lights at once. Whole sites with sheds and plant go bigger. Here's how to size portable generators and meet site rules.
Power for a whole commercial job, with site offices, lighting towers and cranes, is a hire company's work and far bigger than anything portable. This guide is for the tradie who throws a generator in the ute. For camping, caravans and home backup, see our generator size guide.
Sizing a Generator for Power Tools
Running Watts From the Tool Plate
Start with the compliance plate on every tool you'll run at the same time. If it only lists amps, multiply by 230 to get watts.
For a rough guide, DR Power's generator wattage worksheet lists typical running watts for jobsite gear. It has a circular saw at 1,400W, a table saw at 1,800W and a reciprocating saw at 1,440W. An air compressor sits at 1,000W and a halogen work light at 1,000W. Those are US 120V tools, so your own plates win every time.
Start-Up Surge From Saws and Compressors
Motors need a kick to get going. Queensland's Electrical Safety Office says motor-operated gear can take two to 10 times its rated load when starting. It lists construction and building trades tools as one of the load types a generator buyer should plan for.
DR Power's worksheet puts starting watts at typically double the running figure for saws, drills and compressors. Only add the biggest one to your total, and start your tools one at a time.
Worked Example for One Tradie
| Tool | Running watts | Start-up watts |
|---|---|---|
| Circular saw | 1,400W | about 2,800W |
| Air compressor | 1,000W | about 2,000W |
| Halogen work light | 1,000W | - |
| Lithium-ion battery charger | 360W | - |
| Total | 3,760W | 6,560W with the saw starting |
Running figures come from DR Power's worksheet, with start-up at its typical double.
Queensland's regulator also says a generator shouldn't run continuously above 80% of its rated capacity. Divide 3,760W by 0.8 and you want at least 4,700W of running output, plus a peak above 6,560W for the saw. That lands you at 7kVA.
Construction Site Electrical Rules
RCD Protection Under AS/NZS 3012
A building site runs under tighter rules than your shed. SafeWork NSW's fact sheet on AS/NZS 3012:2019 says all electrical equipment on site must be supplied from an RCD-protected circuit rated at no more than 30mA. The RCD can sit at the switchboard, in the socket outlet, or in a portable outlet assembly.
So check your generator before it goes on site. The Welling & Crossley WC-P13750RCD comes with RCD protection built in. Gentech sells an earth leakage protection unit in 15A, 20A and 32A ratings, which its listing says meets Australian Standards for worksite use.
The fact sheet also says generators must be connected in line with AS/NZS 3010. On a managed site, ask the principal contractor's electrician how yours should hook up, and check your own state regulator's rules.
Test and Tag Every 3 Months
The same fact sheet says portable equipment and extension leads on construction sites get tested every 3 months. That covers the leads running off your generator too, so keep the tags current.
Construction Site Generators by Job Size
One Tradie: 3kVA to 6kVA
For one or two tools at a time, a small open frame does the job. The Gentech EP3400HSR is 3.4kVA, 40kg and $1,239.
The Gentech EP5900HSR steps up to 5.9kVA at 70kg and 68 dBA at 7 metres, for $2,189. Its 6.1 litre tank lasts 2.6 hours at 80% load, so carry a jerry can.
Small Crew: 7kVA to 8.5kVA
For a saw, a compressor and lights together, go 7kVA. The Gentech EP7000HSR gives about 5,600W at its 0.8 power factor, weighs 75kg and runs at 69 dBA at 7 metres, from $2,389. The Westinghouse WHXC8500E runs at 6,750W, peaks at 8,500W and has electric start, for $2,399.
If you weld, the Gentech EP200WELDHSR puts a 200 amp welder at a 60% duty cycle and 7kVA of 230V power in one 100kg machine, from $3,290. See the welding generators.
Three-Phase Machinery and Diesel
If your machinery runs on three-phase, a single-phase generator won't run it. The Gentech ED6800YSRE-3 is a 6.8kVA Yanmar diesel with a 20A three-phase outlet and two 15A single-phase outlets. It weighs 100.5kg and costs $8,600.
Diesel costs more up front but less per hour on long days, which is covered in petrol vs diesel generators. Don't oversize a diesel to be safe, though. Caterpillar says running one below 30% of its rated output for long periods causes wet stacking. Browse the diesel generators.
For most tradies, it's a 7kVA open frame with RCD protection sorted. Which one's for you? Tell us the tools you run together and we'll size it with you. Ring the store on 03 7056 6732, text 0476 330 590, or try the generator finder.
