How do I determine how many branch circuits I can add to my breaker panel? would like to add at least two?

Question

I checked the panel and it is a 100 amp unit with 2 empty spaces for 16 spaces total. Branch circuit total amperage adds up to about 210. This house(trailer) has gas heat, electric dryer, gas range, electric water heater. I would like to add 2-20amp branch circuits. One for a small work area and another one dedicated to the air conditioner. When ever I turn on the air conditioner and use a hand power tool in the shop, the breaker snaps off. This is in Montana and I have had plenty of experience adding circuits. I was just a bit foggy on the panel capacity. Wouldn't this be a good way to go? thanks

Answer 1

First, what is the breaker rated at in amps?  I am going to assume that you are doing a residentail circuit (120vac)  Second, it really depends on what state you live in for the NEMA code that would apply.  If you just want to run a branch for a low draw like a table lamp or somthing like that you could get away with 2.  If you are trying to put in an air conditioner, coffee maker or other high draw items you might want to think twice about doing it yourself and get an electrician.  Third thing is how far away are you looking to run the branch?  A simple low speed fan can trip the circuit breaker if it is far enough away due to voltage drop.  Good luck.

Answer 2

Look to see how many blank spaces don't have breakers installed in them. The blank spaces will probably have numbers beside them and rectangular indentations that can be broken out to put breakers in. If you take the cover off (BE CAREFUL) you will be able to see where the breakers plug in. I believe that you should be able to put in as many breakers as there are spaces for.

Edit 1

I think that adding a 20A branch circuit dedicated to the air conditioner and another for your shop workshop is the best thing to do.

A 100A panel is rated 100A at 240 volts, so each of the two hot lines is rated 100A. Half of the 120V breakers will be on each hot line, so each pair of 20A breakers would draw a maximum of 20A at 240V. The 240V breakers will be connected to both hots. Because it is very unlikely that all of the circuits in a panel will be fully loaded at the same time, panels have provisions for installing circuits that add up to more than the rated current of the panel. I believe that the National Electric Code (NEC) permits all of the available spaces to have breakers installed, but I have not found that in my 1996 edition and I can’t get into the on-line NEC. I believe that NEC requires the service conductors and the main breaker of fuses to be rated 100A.