How to Determine Your Circuit Breaker Panel Capacity

There are 4 main ways to determine the capacity of your house’s circuit breakers panel. This panel is usually referred to as the breaker panel, or electrical panel. This article will list those 4 methods and then give a short description of each method. None is more correct than the other. The 4 methods to determine ampacity are listed below.

  1. Determine listed ampacity for the Service Entrance Cable, or SEC.
  2. Determine ampacity rating of the electrical service meter and base.
  3. Determine the value of the main input breaker.
  4. Determine the overall ampacity of the panel and busses.

Service Entrance Cable Ampacity

Determining Service Entrance Cable ampacity by formula is a function of size and ambient temperature. The bigger or thicker the wire and/or the colder the outside air, the higher the ampacity will be. The way to easily and visually determine power handling capability of your service cable is as follows:

  1. Look at the cable label. It will give you voltage and power ratings.
  2. Divide the power rating by the voltage rating to determine the amount of amps the cable is capable of carry. The rated voltage for most service cables is 600 volts.
  3. Most households are fed by 240 volts, split into two cables at 120 volts apiece.
  4. 120 volts is approximately 1/5 of 600 volts.
  5. To determine the 120 volt ampacity of the service cable, multiply the 600 volt ampacity by 5.
  6. A cable capable of handling 2400 watts at 600 volts can deliver  4 amperes at 600 volts or 20 amperes at 120 volts.

Service Meter Ampacity

Service meters are rated for total power dissipation. To determine this rating, look for and read the sticker that will be on the side of the meter. This tag will also specify maximum voltage and power that the service meter is capable of handling. Service meter bases are typically rated the same as the meter, but not always. To determine the service meter base rating, contact a qualify inspector or electrician.

Main Input Breaker Rating

Though this is not an accurate measure of what the panel is able to actually handle, or what the service cables are capable of supplying, this is an accurate representation of the maximum that is currently able to be supplied by the electrical service panel. This measurement is found by simply reading the label on the breaker handle.

Panel and Buss Ratings

More important than the other 3 ratings, the panel and buss ratings will be your best guide for the total amount of power or current that your circuit breakers panel will safely handle. There will be a tag on the inside, usually on the door, of the breaker panel that lists maximum voltage, current and power dissipation capability for the panel and busses. This reading can’t be modified or expanded the way the other ratings can by simple substitution of a higher rated component.

Having read this article, you will now be able to determine the various capacity ratings of your home main electrical service panel.