Select the correct transformer kVA rating for your lighting or electrical load. Enter all loads, apply demand and growth factors, and get a recommendation from standard kVA sizes.
Please add at least one load with a valid wattage.
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A transformer must be large enough for the load it serves, with some margin for growth. Add up the loads in volt amperes, apply a demand factor if not everything will run at once, add a margin for future expansion, often about 20 to 25 percent, and divide by 1,000 to get kilovolt amperes. Then choose the next standard transformer size above the result.
Standard sizes come in steps, such as 15, 25, 37.5, and 50 kilovolt amperes for single phase and 30, 45, 75, and 112.5 for three phase, so the transformer you buy is usually somewhat larger than the calculated figure. For a three phase system, the kilovolt amperes equal the square root of three times the voltage and the current, divided by 1,000.
LED drivers and some other electronic loads draw a large inrush current when they are switched on, which can trip protection even when the running load is small, so check the inrush as well. Consider the temperature, the ventilation, and the impedance of the transformer, which also affects the fault current. A qualified engineer should confirm the selection.