How to Calculate Power Requirements for a Construction Site

Step 1: List Every Tool and Appliance

Start by listing every piece of equipment that will draw power on site. This includes:

• Power tools: drills, circular saws, angle grinders, jackhammers
• Site amenities: lighting towers, kettles, microwaves, fridges
• Heavy equipment: concrete mixers, welders, compressors, pumps
• Office equipment: laptops, phones chargers, printers

Step 2: Find the Running Wattage

Check the data plate on each tool or its manual. This tells you the running wattage — the power the tool needs to keep operating. If only amps are listed, multiply amps by 240 (standard Australian voltage) to get watts.

Step 3: Account for Startup Surges

This is where most site power calculations go wrong. Inductive loads — anything with a motor (compressors, pumps, cement mixers) — draw 3-4 times their running wattage for the first few seconds when starting up.

Rule of thumb: Add a 20% buffer to your total running wattage to cover simultaneous startups and unexpected loads.

Step 4: Total Your Peak Demand

Add up all running wattages, then apply your 20% buffer. This gives you your peak demand — the maximum power your site will draw at any one time.

Step 5: Size Your Generator

Choose a generator with a continuous rating at least 25% above your peak demand. This headroom prevents overload, reduces fuel consumption, and extends the generator's lifespan.

For example:

| Total running wattage | 45 kW | | --- | --- | | + 20% buffer | 54 kW | | + 25% headroom | 67.5 kW |

A 60-80 kVA diesel generator would be suitable for this scenario.

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