# How do you calculate how many amps you need for a new shop?

 Forum topic by Rob posted 02-06-2014 05:34 AM 21980 views 0 times favorited 46 replies
 Rob704 posts in 3274 days 02-06-2014 05:34 AM I’ve finally decided that I’m wasting too much time dinking around with my minimal set of power tools, and if I can scrape together enough money I’m going to clear out my single-car garage this spring and convert about half of it into a small woodshop. (Unfortunately I still need to share space with the mower, grill, bicycles, etc.) The biggest problem is, it has minimal wiring…an outlet in the ceiling for the garage door opener, and may one or two double outlets on the one wall shared with the house. I know that’s not going to be enough to run my tools, because I already trip the breaker every time I try to use two tools at once. At first it seemed obvious how to calculate the number of amps I’ll need: just add up the amps from all the tools, and give that number to the electrician. But I’ll never use all the tools simultaneously, so that seems excessive. If I have a list of tools that I have or plan on getting, how do I calculate how many amps I need? Do I just add up the amps on all the tools that will be running at the same time, and tack on an extra 20A or so for breathing room? Or do I have to also figure out where each tool will be, which outlets will be on separate circuits, etc.? For example, the largest assortment of tools and other electric devices I could see myself running at one time would be the air compressor, the dust collector, a shop vac, the lights, cordless drill chargers, computer, garage door, an A/C or heater, and either two random orbit sanders or a saw (table, miter, circular, or jigsaw). Suppose all that adds up to 100A. 1. Does that mean I just need to tell the electrician I need 100-120A in the garage? Or do I add up all my tools, put each pair of outlets on a separate circuit, multiply the number outlets by 15-20A, and give him that number so I never have to worry about tripping the breaker? How much breathing room do I need? 2. Should the 110V circuits be 15A or 20A? (I don’t think any of my tools have a 20A plug, but I think the dust collector is technically rated at 20A.) 3. Since most tools are rated at 12-15A, does it make sense to just put each pair of outlets on a dedicated circuit? -- Ask an expert or be the expert - http://woodworking.stackexchange.com