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What Size DG Set Do You Need for a Construction Site?
A DG set that is too small trips every time a motor starts. One that is too big burns extra diesel all day. Choosing the right kVA for a construction site is not difficult once you know the method. This guide walks through it step by step.
Step 1: List every machine that will run together
Write down the machines that will run at the same time, not every machine on site. A typical list might include a concrete mixer, a mini lift or monkey crane, a water or mud pump, lighting and hand tools such as drills and cutters.
Step 2: Note the power of each machine in kW
Check the motor nameplate. If the rating is in HP, convert it: 1 HP ≈ 0.75 kW. Add up the running load of everything on your list.
Step 3: Convert kW to kVA
DG sets are rated in kVA. For most site loads, use a power factor of about 0.8:
kVA = total kW ÷ 0.8
Step 4: Allow for motor starting
Electric motors draw several times their running current for a moment when they start. A DG set sized only for the running load can trip or stall when a big motor starts. To handle this:
- Start the largest motors one at a time, not together.
- Add a margin on top of the running kVA. Motors with star-delta or soft starters need less margin than direct-on-line starting.
Step 5: Keep a working margin
Do not plan to run the DG set at full load all day. Aim for it to run at roughly 70–80% of its rating. This saves fuel, reduces wear and leaves room for an extra tool.
A simple example
Suppose these run together on a site:
| Load | Approx. power |
|---|---|
| Concrete mixer motor (7.5 HP) | 5.6 kW |
| Mini lift winch motor (10 HP) | 7.5 kW |
| Lighting and hand tools | 3 kW |
| Total running load | 16.1 kW |
16.1 kW ÷ 0.8 = about 20 kVA running. Adding margin for motor starting and to keep the set below full load, a 25–30 kVA DG set is a sensible choice for this site. These figures are only an illustration. Use the actual nameplate ratings of your machines.
Other things to check
- Single-phase or three-phase: most site machines need three-phase supply.
- Portability: a DG set on a trolley or base is easier to move around the site.
- Fuel tank size: enough for a full shift without refilling.
- Service support: parts and service close to your site.
Need help choosing?
Santosh Industries supplies DG sets for construction sites along with concrete mixers, mini lifts and other machinery from Jodhpur, Rajasthan. Send us your list of machines through the quote form, call +91 82906 96409, or call or WhatsApp +91 70141 66256, and we will suggest the right size.
Frequently asked questions
How do I calculate the kVA of a DG set for a construction site?
Add the running power (kW) of all machines that run together, divide by 0.8 to get kVA, then add margin for motor starting so the set runs at about 70–80% of its rating.
Why does my DG set trip when a machine starts?
Motors draw a high current for a moment when starting. If the DG set has no margin for this, it trips. Start large motors one at a time or choose a bigger set.
How do I convert HP to kW?
Multiply HP by about 0.75. For example, a 10 HP motor is about 7.5 kW.
Should a DG set run at full load?
No. Running at about 70–80% of its rating saves fuel and extends its life.
