Calculating Your Home Circuit Load Capacity
If you calculate your circuit load capacity you can get a good idea of the size of the electrical service that you require. The calculation is quite simple because you have to add together two components: your power consumption and the power used by your electrical appliances.
You should keep your circuit load at 80% of the total circuit load. This means, that if your circuit is 15 amps, it is best not to exceed a circuit load of 12 amps. If the total wattage in your house is limited to 1800 watts, it is safest to use wattage of about 1440 watts.
Similarly, for a 20-amp circuit available in your house, your usage should be limited to 16 amps. Again, use only 1920 watts if the total wattage is limited to 2400 watts. For a 30-amp circuit it is safe to use only up to 24 amps. If wattage is up to 3600 watts, keep the limit of usage up to 2880 watts.
The calculation of the wattage is by calculating the voltage multiplied by the amperage. The required amperage rating is mentioned on all the electrical appliances. Look at the lighting load of each bulb and add them all up. The wattage for each bulb is printed on it.
Water heaters, air conditioners, electric dryers and electric ranges are 240-volt appliances in your home. Each appliance again has an amperage rating label and you can calculate the wattage accordingly. This can be done by taking the voltage which is 240 volts, multiplying it with the amperage, for example 30 amps, which will give you the wattage requirements.
Once you have done all these calculations you can instruct your electrical contractors about the total load that is required for your home electrical system, and decide on the size of the electrical service.