main panel capacity

[jimbo]

hello,i've got a 150amp main and i want to install a 70amp breaker and run feeder out to a subpanel in my detached garage.there will be a circuit for recepticles,one for the lights,and a 220 recepticle for my electric welder.my house is only 1200 sq.ft,but i have a 50amp breaker for the heat...a 40amp for the range...and 3-30amps for the dryer,a/c,and hot water heater.i also have 6-15amp and 7-20amp breakers.will the 70amp breaker overload the main.do i even need a 70 amp or could i go smaller.i plan on using #4/3 uf with a gounding rod at the garage.thanks and any help would be appreciated.

[rlfrazee]

Jimbo look above at the tabs (yellow and green) click on detached garage. Should answer alot of your questions while you wait for replies.....RL

[Wgoodrich]

You could have 300 amps or more of total amp branch circuits in that 150 amp panel and it may not be overloaded.

The proper method of finding load of that service panel is to perform a demand load calculation. This calculation format approaches intermittent load values. Just because you have the breakers in that panel does not mean you have that much load. Intermittent load comes into play very strongly with residential services.

As rlfrazee directed you to the top of the page to hit the detached garage article explianing how to wire a detached garage and its power source choices, you also should look to the top of this page for the box that says "demand load calc". Click that and you will open an article providing a format of calculation to discover the demand load of your home. The answer you find following that demand load format calculation there will tell you how much load is being applied to that service. Article 220 tells us that you must size your service by calculating a demand load calculation. The link above is the general method of demand load calcultion, there also is an optional method of calculation found in the NEC Chapter 2 if you can figure it out without further explaination but what is in the Code.

Good Luck

Wg