Turning a kVA rating into amps you can plan with

A hire company offers a 60 kVA set. The site needs to know whether the existing supply and cabling can take it.

Sixty kilovolt-amperes is not an answer to that question. Amps are, and getting from one to the other needs two more pieces of information that the headline number leaves out.

Voltage first, then phases

Apparent power is voltage times current, so turning kVA into amps means dividing by the voltage. On single phase that is the whole calculation.

Ten kVA at 240 V is 10,000 divided by 240, which is 41.7 A. At 120 V the same 10 kVA is 83.3 A, because halving the voltage doubles the current for the same power. That relationship is why higher voltages are used for anything substantial, and why 12 V systems need such heavy cable.

Three phase carries a square root

On a three phase supply the formula gains a factor of the square root of three, roughly 1.732. Amps equal kVA times 1,000, divided by line voltage, divided by 1.732.

So 10 kVA on a 400 V three phase supply is 14.4 A per line, not the 25 A the single phase formula would suggest. The root three is there because the three phases are 120 degrees apart and do not peak together, so the arithmetic is not a simple product.

Apply the single phase formula to a three phase load and the answer comes out 73% high. Apply the three phase formula to single phase and it comes out 42% low, which is the dangerous direction, because the cable and protection get sized for less current than will actually flow.

Use the line to line voltage

Three phase supplies are usually quoted as a pair, such as 400 over 230 V or 208 over 120 V. The formula wants the larger figure, the line to line voltage.

Reaching for the smaller number is a common slip, and it inflates the calculated current rather than understating it, so it tends to produce an expensive overspecification rather than an unsafe one. Worth catching either way.

Working the other direction

Most of the time the real question runs backwards. You know the load in kW and need to know what size machine or supply it demands.

Divide the kW by the power factor to get kVA, then convert to amps with the formula above. A 24 kW load at 0.8 power factor is 30 kVA, which on 400 V three phase is 43.3 A per line. The kVA calculator runs all of these conversions in both directions so the root three never has to be remembered under pressure.

Then take that current figure to the cable. Conductors are sized on amps, not on kVA, and that sizing has to survive both the heat limit and the voltage drop over the run. The wire gauge calculator covers both, which matters particularly for a temporary supply where the generator often sits a long way from the load.

The outlets are usually the real ceiling

A detail that catches people out on hire equipment. The machine’s total rating and what any one socket can deliver are different numbers.

A set rated at 60 kVA might offer a few large outlets and several 16 A ones. If the actual load is spread across the small sockets, the usable capacity is whatever those outlets add up to, not the figure on the side of the machine. Check the panel, not the nameplate, before assuming a machine covers the job.

A sanity check worth keeping

For 400 V three phase, amps are roughly 1.44 times the kVA. For 240 V single phase, amps are roughly 4.2 times the kVA. For 120 V, roughly 8.3 times.

Those ratios will not pass an inspection, but they are enough to notice when a calculated figure is out by a factor that matters, which is the most common way these conversions go wrong.