Subpanel Install...enough Power Available? - Electrical - DIY Chatroom Home Improvement Forum

Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Electrical


Thread Tools Display Modes
Old 01-03-2013, 06:23 PM   #1
Join Date: Jan 2013
Posts: 2
Rewards Points: 10

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


joeyflaum is offline   Reply With Quote
Old 01-03-2013, 06:34 PM   #2
Civil Engineer
Join Date: Mar 2009
Location: Boston
Posts: 5,641
Rewards Points: 4,862

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.


Daniel Holzman is online now   Reply With Quote
Old 01-03-2013, 06:58 PM   #3
Lic Electrical Inspector
electures's Avatar
Join Date: Dec 2009
Location: The Great Police State of New Jersey
Posts: 1,826
Rewards Points: 1,108

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.
All responses based on the 2011 NEC.
If you live in New Jersey click here. All other states click here.
Please check with local, county and state officials as laws may vary.
Sizing motors here. Online motor calculator here. Online calculators here.
electures is offline   Reply With Quote
The Following User Says Thank You to electures For This Useful Post:
NJMarine (01-04-2013)
Old 01-04-2013, 01:06 AM   #4
ddawg16's Avatar
Join Date: Aug 2011
Location: S. California
Posts: 11,413
Rewards Points: 1,980
Blog Entries: 2

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 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 no heat or 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 a load analysis....
Even if you are on the right track, you will still get run over if you just sit there.

My 2-Story Addition Build in Progress Link ... My Garage Build Link and My Jeep Build Link
ddawg16 is offline   Reply With Quote

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Back up generator for main panel in power outage. Greenie Electrical 44 07-29-2015 10:57 PM
Hot tub subpanel install, any subpanel Maxian Electrical 5 11-07-2012 04:01 PM
How can I install a power switch on my compressor? sofasurfer Electrical 1 09-27-2010 03:04 AM
running power outdoor to subpanel beerdog Electrical 2 02-15-2010 11:31 AM
Help w/ new light install DaveS60R Electrical 3 03-12-2009 08:54 PM

Top of Page | View New Posts


Search Engine Friendly URLs by vBSEO 3.6.1