Woodshop Electrical Requirements - Concurrently running tools

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Forum topic by William Shelley posted 01-08-2017 08:48 PM 2676 views 0 times favorited 24 replies Add to Favorites Watch
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William Shelley

587 posts in 1617 days

01-08-2017 08:48 PM

I’m currently planning out a new woodshop that will be approximately 14ft x 28ft. It’s attached to the house, but due to the distance from the house’s load center, I think it will be preferable to install a new small subpanel.

With that, I’m trying to size the feeder for the sub. I realize it doesn’t make sense to consider ALL the tools that will be in the shop, only the ones that are running at the same time. The absolute most I can think of, which factors in future upgrades to my existing tools, would be:

Lights: 120V, 120W x 8 fixtures = 8A
Dust Collector: 240v, 3-5HP = 10-16A
Tool in use: 240v, 3-5HP = 10-16A
Air compressor: 240V, 5HP = 16A
Electric heat: 240V, 2500W x 2 heaters = 21A

I added in the air compressor because it could kick on during operation of anything else.

This gives me a total running load of 77A. Because breakers need to be sized so that the full load does not exceed 80% of the rated amps, I would need to go up to a 100A feeder. If I ditched the heaters off the shop subpanel or used gas heaters I could likely get away with a lot less.

Am I missing anything? I’m also unsure as to whether 5HP is a reasonable allowance for an air compressor in a woodshop. I could see an auto-body or machine shop needing a lot of air for running hungry tools but I imagine I might be fine with a 2HP compressor realistically.

-- Woodworking from an engineer's perspective

24 replies so far

View bbasiaga's profile


1240 posts in 2142 days

#1 posted 01-08-2017 09:03 PM

Seems like you are on the right track. I don’t know how much air you plan to use, but I’ve got a 20gal 110V from one of the big box stores. I only charge it up when I’m going to use it, and I can nail a lot before it has to kick back on. If you are going to blow a lot, or use it for spraying, you’ll want the biggest one you can get. I spray with a separate HVLP system, so not a concern with me. I also don’t use an air powered grinder or anything. Is this a production shop or a hobby shop?

If you’ve got a way to go to gas heaters easily it will cost you more up front, but save you a ton of operating cost. I’d highly recommend it.


-- Part of engineering is to know when to put your calculator down and pick up your tools.

View rwe2156's profile


3092 posts in 1628 days

#2 posted 01-08-2017 10:29 PM

First, I am not an electrician I know enough to be dangerous BUT I’ve done quite a bit of wiring in my life and so far, nothing has burned down.

Second, I STRONGLY urge you to consult an electrician before you do anything.

I don’t think you can calculate the load that way. You’ll never draw that many amps with all the machines running. Correct me if I’m wrong, but amperage rating on motors is usually FLA (full load amps). The only machine that would come close is a compressor (when running).

I ran my entire shop on a 60A feed that was a 1200 sf shop with a 5HP compressor, 240V arc welder, 2/3HP, 2/2HP machines and a dust collector plus about 20 8’ T12 lights. Never had a problem at all. I would suggest a portable 2HP compressor that way you have flexibility to move it around.

I think a 60A service should work. You can use split breakers for 120 if you need more room in the box. You can put all your 240V machines in one circuit. The compressor and DC should be on dedicated circuits. Lights and outlets on separate circuits.

5HP compressor is WAY too big for a ww’ing shop. I have a 5HP 80gal compressor in my mechanic shop that feeds the airlines in my ww’ing shop. It is a beast and pulls ALOT of juice when its running.

Similarly, a 5HP tablesaw is totally unnecessary expense for the average ww’er. They are applicable to a commercial shop with power feeders.

Also for a shop that size a 5HP DC would also be overkill IMO.

Bottom line: I think your overestimating what it will take to run your shop.

Once again, PLEASE consult an electrician. I learned by experience you can hire a young man to moonlight a job and get lots of freebies, too like wire. They can also buy the materials far cheaper than you can. The savings on the wire and conduit alone will offset the labor expense quite a bit.

Also, I recommend running all your circuits in conduit or armorflex. The lighting is much easier to wire and you will be able to change/add/extend circuits or add outlets and switches very easily.

-- Everything is a prototype thats why its one of a kind!!

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William Shelley

587 posts in 1617 days

#3 posted 01-08-2017 10:39 PM

Thanks for the input. I did consult an electrician (me). I currently have a Husky 30gal air compressor with I think a 1.5HP or 2HP motor, i have the HF 2HP dust collector, and I realize that tools don’t draw their FLA all the time but when they do is usually when it’s most inconvenient…

I’ll look into gas heaters though, although the ceilings may not be tall enough (12ft sloping down to 8.5ft) to hang a gas heater.

-- Woodworking from an engineer's perspective

View Rob_s's profile


251 posts in 769 days

#4 posted 01-08-2017 10:41 PM

I’m finding, personally, compressed air to be much less of a requirement in today’s shops due to the availability of 18v cordless replacements for many of the tools. I went with a California Air Tools 11v 10 gallon because of this and am pretty happy so far. So you might not need a massive compressor either.


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William Shelley

587 posts in 1617 days

#5 posted 01-08-2017 10:52 PM

Rob – agree 100%. I don’t even own a corded drill, and the only reason right now I would think of buying one is if I needed it to mix things, e.g. drywall mud or thinset.

That being said, I really like with air-powered drills is that the air typically blows out of the bottom of the handle so clearing the dust from around a hole you just drilled takes half a second at most.

-- Woodworking from an engineer's perspective

View MrUnix's profile (online now)


6943 posts in 2346 days

#6 posted 01-08-2017 10:59 PM

I’m finding, personally, compressed air to be much less of a requirement in today’s shops due to the availability of 18v cordless replacements for many of the tools.
- Rob_s

Do you do any finish spraying or media blasting? I don’t use air powered tools often, but I do spray a lot of stuff and couldn’t do most of it without a decent sized compressor. Ditto for media blasting. If all I were using it for was to blow chips off the workbench or fill up pneumatic tires, then a smaller one would certainly work, although it does limit what you can do with it in the future should the need arise.


-- Brad in FL - In Dog I trust... everything else is questionable

View splintergroup's profile


2310 posts in 1370 days

#7 posted 01-08-2017 11:49 PM

I agree with Unix, I have a 60 gallon 6HP and it’ll run constantly when I’m spraying or when I’m flushing the irrigation system 8^)

My sub panel is 60A, never had any issues, but my DC (2HP) is never run when I’m running my compressor. Typically I’ll fire it up at the start of the day then shut it off. Plenty of air for the general stuff but that extra oomph pays off when needed.

If you really want airflow, a two stage will fit the bill, but that’s when things get pricey.

Dropping the electric heat would be the first thing I’d do. Electric heat is high dollar, especially if you have gas available (assuming the cost of the swap is reasonable).

View JBrow's profile


1366 posts in 1067 days

#8 posted 01-09-2017 02:00 AM

William Shelley,

By my way of thinking, the most difficult part of the upgrade is running the feeder cable. Replacing an undersized load center can also be a difficult chore. While your load calculations may be spot on, having additional and perhaps never needed capacity can save from having to re-do rather difficult tasks later on should you guess wrong. Having the ability to upgrade electric service later on could be as simple as doing nothing or swapping out an undersized breaker. If the additional capacity is never needed, I guess it is a waste of a few dollars. But that is balanced considerable cost of re-doing the electric to get the added capacity should it be needed.

View OSB's profile


147 posts in 673 days

#9 posted 01-09-2017 04:01 AM

You probably won’t leave the compressor on 24/7, I suggest you leave it off when you know you are going to use your dust collector and a high current tool.

LED lights would not need a kilowatt.

Insulation will work out cheaper than electric heat pretty quick.

If you ever see yourself needing a phase converter for some big boy toys, you might want to budget for more power but if you have your woodworking habit under control, you could try to get by with less than you have planned probably.

View runswithscissors's profile


2843 posts in 2172 days

#10 posted 01-09-2017 04:01 AM

When I was doing my shop, I looked at 60 amp panels. The guy in the hardware store (a real one, not a BORG) pointed out that a 100 amp panel would actually cost less, and would give me the capacity to expand if needed. I heeded his advice, and have not regretted it.

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

View Fred Hargis's profile

Fred Hargis

5095 posts in 2641 days

#11 posted 01-09-2017 12:30 PM

Ditto everything above: the 100 amp isn’t going to cost that much more than anything smaller, start with it and don’t look back even if you think it’s overkill. Keep the cpmpressor switched off, unless it’s in use. Here’s why: a sudden failure like a burst hose could happen when you’re not in the shop and start it running. It will keep running and could catch fire is it overheats…at the very least it could use a lot of juice if it runs for a long time. Lastly, if at all possible, choose a heat source other than electric. You may find you need to keep the shop heated to above freezing all the time (to protect some finishes, glue, and whatever) and electric heat will challenge your will to do so.

-- Our village hasn't lost it's idiot, he was elected to congress.

View rwe2156's profile


3092 posts in 1628 days

#12 posted 01-09-2017 01:31 PM

William if you’re an electrician you should know you don’t size a service panel for everything on at full load all the time. I’ll bet if you check your main panel and add up the breakers it exceeds the main breaker amperage.

I’ve had 3 service panels installed by electricians over the last 10 years I’ve asked them about the load aspect. They all told me you the same thing: you size a panel more by the # of circuits you need than the amp draw.

As you know, the key is dedicated circuits for compressors, DC, etc. You should be able to run your entire shop on a 60A subpanel. I did for years with no problems, and that included a 5HP beast of a compressor.

-- Everything is a prototype thats why its one of a kind!!

View OggieOglethorpe's profile


1276 posts in 2257 days

#13 posted 01-09-2017 02:49 PM

I think your DC circuit is too small if you really plan to go over 3HP.

I have a 3HP JDS cyclone, and it’s on a 30A circuit. Startup current is in the 80A range for a few seconds, then it ramps down to about 18A and stays there. I know this because I had a bunch of issues with remote controls back when I installed the unit, and we did a bunch of real world measurements to determine actual needs.

You can also keep in mind that machines like planers, jointers, and saws when up to steady speed and running no-load, use far less power than under load. I have a SawStop 3HP ICS and DJ-20 running on the same 20A circuit (I know, virtual electricians… ;^)) and often leave both running as I go back and forth ripping and edge jointing in my one man shop with no issues at all.

View LittleShaver's profile


398 posts in 767 days

#14 posted 01-09-2017 03:00 PM

Go big. Leave yourself room for expansion and a possible second user. Who knows what your future needs will be.

-- Sawdust Maker

View William Shelley's profile

William Shelley

587 posts in 1617 days

#15 posted 01-09-2017 03:17 PM

Lots of good points here. There’s a significant price jump after 60A, for example the feeder breaker in my main panel costs $9 for a 60A, 2-pole, or $35 for a 70A, 2-pole. Wire gauge is also a factor.

I typically oversize the wires on branch circuits that are running a lot, or have really high inrush current demands. For instance, I ran 8awg for a 30A, 240v feed to my rack of computer server equipment because it runs 24/7 and draws in excess of 3500w with everything on.

The air compressor and possibly dust collector should be the only tools that actually start under load, I think I will oversize the wires for these circuits.

I might stick with electric heat just because the cheapest gas heater I can find starts at almost $400, and that doesn’t include the cost of getting the gas plumbed into the shop. I have access to tons and tons of 4” and 5” thick polyurethane isocyanate insulation surplus from my workplace, it’s R-7 per inch so 2×6 walls with that much insulation should maintain temperature pretty well even with like a small portable electric heater (for now).

-- Woodworking from an engineer's perspective

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