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-   -   subpanel install...enough power available? (http://www.diychatroom.com/f18/subpanel-install-enough-power-available-168172/)

joeyflaum 01-03-2013 06:23 PM

subpanel install...enough power available?
 
Hi everyone,
I want to install a subpanel in the garage for my woodworking shop. Probably anywhere from 60 to 100 amps. The house runs on 200amp service. there are a few slots open in the box but everything in the house runs on electric and all of the breakers equal up to more than the 200amps. I realize that not everything will be running at the same time and I know I need professional help with this but i am just trying to see if i will need to upgrade the service or if i can work with what i have.
thanks all

Daniel Holzman 01-03-2013 06:34 PM

This is a very common question on this forum. You need to do a load analysis, which will account for the fact that only a fraction of the total potential power is likely to be required at any given time. The National Electrical Code contains a method for performing the analysis, I can't quote the section, but a competent electrician can perform the analysis, or you can try it yourself.

electures 01-03-2013 06:58 PM

The fact that the sum of the branch circuit devices exceeds the main breaker rating is irrelevant. It all has to do with the calculated load. The calculated load of the existing dwelling plus the calculated load of the new garage loads cannot exceed the rating of the service entrance conductors. In your case 200A.

ddawg16 01-04-2013 01:06 AM

Joey....I do woodworking as a hobby....

Unless you and a few other people are out there at the same time running a bunch of power tools, you really don't need that much power out there. I'm feeding my garage with a 50A breaker and have never tripped it....except for that time I drove the ground rod through the counduit....couldn't have aimed it any better......

Like the guys above said, do a load calculation....Cliff note version...you add up the loads for things that can run at the same time. In the case of the garage, your most likely full load will be all lights on, air compressor running and your biggest tool (table saw). Of course if you have an AC unit or electric heater, then that has to be factored in.

I'm in California...so no heat or AC...so my worst case load is 7A for the compressor (240Vac), 5A for lights and 15A for the table saw. Total worst case 22A. (lights are on the other leg from the table saw).

With that said...having a little extra power is ok.....

But like the guys said....do a load analysis....


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