I am trying to figure the capacity of my breaker box. Looking at the main breaker and lugs, there is two sides. So my question is, if the main breaker is a 100 amps; is the capacity of the box 100 amps per side (being 200 amps total), or 100 amps total and only 50 amps per side. The breaker reads 100 amps on each side, but the print on one side looks like it was purposely erased.

Each pole allows 100 amp per hot leg. You can consider it as having 200 amps of 120 volt load. But we never think of it that way. The breaker is rated to operate at 80%, so you only have 80 amps of capacity.


If your planning to add a substantial load, the important issue is calculated connected load. What are you adding and give total square foot of livable space, list all major electric appliances. Type of heat. Size of AC. I can do the calcs to see if you have ample capacity.

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Originally Posted by tkrussell

If your planning to add a substantial load, the important issue is calculated connected load. What are you adding and give total square foot of livable space, list all major electric appliances. type of heat. size of AC. I can do the calcs to see if you have ample capacity.

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Question for tkrussell, Calculating the amount of Amps for figuring out capacity
Sounds like something we need to all learn to keep things working and for the
Sake of safety too. Would you be kind enough to give us a lesson on this, or point
To a url that we can read ourselves, it would be greatly appreciate it.

Located in the sticky note at the beginning of the electrical forum is :
https://www.askmehelpdesk.com/electr...ons-48863.html

That contains a link, with instructions, to review the actual National Electric Code. See Article 220, and the examples at the back of the book.


This is somewhat difficult to understand and not easily learned casually.

This is not something a layperson should attempt, unless the article is completely understood. Any errors will result in improperly sized services.

You may try secondary education for electrical code courses. There may be training books out, but none I know of.

I guess in a round about way I am saying I will not be teaching this topic from the beginning. If you can come back with specific questions or examples, I will be glad to help.

I couldn't imagine trying to learn load calc's on an online forum! I'd sooner try to give a bobcat a backrub in a phonebooth...