SJE Electrical Installations.
Generator size?
The only difference between kW and kVA is the power factor. The power factor, unless known, is an approximation, (0.8 for this calculation). The kVA value is always higher than the value for kW.
First total up your expected emergency generator power needs (watts) these figures can be found on appliances. (do not confuse (A amps) or (V voltage.) or Hz frequency.
If unsure, allow 100 watts per lighting point, 150 watts tv, 60 watts fridge/freezer, 50 watts gas/oil/solid fuel central heating pump and associated controls, 100 watts computer, 2000 watts electric kettle.
For this example we would like to cover 5 lighting points, 1 tv point, 1 fridge/freezer, 1 computer, 1 central heating point and 1 kettle. Therefore the total power required is 2860 watts, divide this figure by 1000 to give kilowatts (kW) = 2.86, which give a generator minimum requirement of 3.57kVA. Always input figures in kW.
*Notice: This calculator is intended for guidance only and absolute reliance should not be placed on the results.
We would ensure that the generator could not be overloaded by installing an overcurrent device, this would trip if the power usage went to 95% of the generators maximum output capability. So care needs taking, using the example above, if someone used an electric shower, or other high power appliance the electricity would be interrupted and the device would have to be reset. A nuisance! We would advise physically switching such devices off at the distribution board so accidents can be avoided. Although modern generators have built in power overload we always advise slightly down sizing the protective device, at the local transfer switch/control.
Of course you can always have a generator installed that will serve any power requirement.
Industry, special requirements
Motors: Attention must be given to the size, type and starting technique for each electric motor.
