wiring panel for room addition

[daudrey5]

I have 200 amp service in my house. I have a 100 amp service in my garage that comes from my house panel. My house panel only has enough room to accomodate 2 breakers. I plan to install another 100 amp breaker in my house panel to run to another service box in my added on room and wire that room from that new box. Can anyone tell me if i can do this? Will i be taking a chance on over loading my house panel? Thanks

[JP]

You should be fine; it all boils down to what current you use at one time. A 200 amp service is really gives you 400 amps, 200 per phase. However you should only ever load it to 80% which is 320 amps. Unless you have a lot going on it is doubtful that you will draw 320 amps at any given moment.  You can get a clamp on amp meter and check each phase to see how much current your house really uses; you can leave it on for a period of time and use the max setting that will remember the highest current draw.