How to Size an A/C Panel Board for a Substation

The electrical power supplied by the utility is divided up into individual branch circuits in the home's distribution panel. Once this panel is full, you will need to install a substation, or sub panel, to add more circuits to the system. The size of the sub panel depends on the electrical service size and the needs of the new circuits in the new panel. Installing an undersized panel can be dangerous, because it won't suit the level of consumption required.

Instructions

- 1
  Look at the breaker on the main electrical disconnect. This number is typically printed in amps on the breaker's switch and is the total amount of power available to the building. The sub panel cannot exceed this number.
- 2
  Determine the wattage of all of the appliances connected to the sub panel. This information is contained in the appliance owner's manuals or on a data plate fastened to the appliances.
- 3
  Input the information into the electrical load calculator (see Resources). Press the "Calculate Load" button.
- 4
  Record the computed amperage at the bottom left of the results. This is the minimum size of sub panel you need to meet the electrical requirements.

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