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



## intelligen

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?


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## Loren

Get a shed first and put all the stuff in it.

Considering your space, unless you're planning to buy a 5-function
combination machine, you're going to have to make some
real compromises with machinery for furniture making.

It's not the panel that will limit you, it's the space itself.

That said you want 20 amp circuits and no, you don't need
dedicated circuits but you may want one to run the dust
collector on itself. It's the simultaneous running of 
machines on one circuit that blows breakers, not the
number of outlets on that single circuit.


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## OhioMike

Normally I would say that a small one-person shop (like mine) can function just fine with a 60 amp (240volt) subpanel. However, since you also want to power your HVAC system from the same subpanel, it might need to be enlarged a bit, depending on the HVAC system requirements.

Your electrician should do these calculations for you.

Remember, a 60A, 240V subpanel can provide up to 120 amps of standard 120 volt circuits.

As for standard receptacles, I would put them all on 20 amp circuits and I would put the lights on a 20 amp circuit too if your local code allows. (Some local codes require lighting circuits to be limited to 15 amps)

Again, your electrician will know the local requirements.

For reference, my small one-person shop has:

Three 20 amp general purpose receptacle circuits. (My 4.5 gallon air compressor shares one of these circuits)
One general purpose 240 volt 20 amp circuit (table saw, planer and jointer)
One dedicated 240 volt 20 amp circuit for the dust collector
One 20 amp circuit for the lighting.

Mike


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## wapakfred

Here's the thing: once you've Decide on a subpanel (and you should do that, if you haven't) the extra cost of 100 over a 60 is fairly minimal. I truly believe that a 60 amp sub would serve you well, but I also believe a 100 amp will give you more slots (more circuits) and plenty of power if you decide to, say, buy a small welder; or some other high current draw tool. Make all your circuits (120V and 240V) 20 amp, and you still have room for any larger ones you might need in the future.


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## jmos

I'm not clear, are you looking at a sub-panel? Being in the garage, I'm guessing your house electrical panel in there. Are you just coming off the main panel, or looking at a sub?

Anyway, I would think you have a lighting circuit already, even if you expand the number of fixtures, you should be fine. I've got 7 2-tube florescent fixtures and a shop air filter on my 15amp lighting circuit, plus a few other regular compact florescent fixtures. Never had any problems.

Assuming everything you have is 110v; 
I would plan on one new circuit for the dust collector, sized for what it needs, 15 or 20amp
another dedicated circuit for the HVAC
maybe one for the air compressor if that is something you use a lot
two 20 amp circuits for tools

You just won't be running that much at one time if it's just you. Now, if you plan on having someone else in the shop with you also running equipment, you may want to reconsider.


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## CharlesA

How many amps do you need for a garage? Depends on how many guitars you got . . .


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## bigblockyeti

That's a tricky one. For example some tools like a dust collector, air cleaner and any fan you might be using will pull close to the nameplate amperage with little deviation except for start up. Tools like the tablesaw will rarely come close to pulling the amperage listed while running, but way more during start up. If you add the amperage of all the tools you have, as well as those you'll likely add in the future, that would provide you with plenty of juice to run everything with lots of capacity to spare! I have a 60 amp service going to my shop and theoretically I could pull nearly 300 amps with the larger tools (the air compressor could pull 36 amps alone). I've never had a problem, but I have to remember that starting any tool while the dust collector and one other tool is already running could trip the 60 amp breaker in the main panel feeding the sub panel.


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## intelligen

Thanks for all the advice, guys!

I'm planning to add a subpanel because I figured it might not cost that much more than running wires all the way to the garage from the main panel in the basement on the other side of the house. I guess that's a question for the electrician.

There is some small welding equipment I'll have to factor that in, but I don't see myself ever using it at the same time as the woodworking equipment. I remember hearing somewhere that intense heat and wood don't get along….

I didn't think about the conversion from 240V to 120V in the panel; that means I'll be able to get by with a lot less than I was thinking before. I'm planning to put in at least a couple 240V circuits for a couple stationary machines and/or welding equipment. I'm leaning toward a 240V table saw but I guess it'll depend on what I can scrounge up for funds.

I'll have to look into whether there's a good place to put a small shed in the back yard for the mower, etc. The real issue is that we have a 4×8 trailer that I probably have to stash in the garage during winter, and it takes up about 1/4 of the garage.

If anyone else has anything to add, keep the advice coming.


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## jmos

If you are doing a sub panel, I agree you should cost out 60, 80, and 100 amp; probably won't be much of a difference. I had to do a sub-panel for my shop and ended up at 80 amp at the same cost as 60amp. You won't want to have to do this twice.

If you're thinking many dedicated 240v circuits, count them up; since they take 2 slots per, you want to make sure your box is large enough.


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## DanLyke

You only need enough to run your largest tool and dust collector simultaneously. That probably means 40A for tools (2 20A circuits), and a lighting circuit (which may exist off your other panels). But I agree with everyone here: There's no reason to not just put in a 100A panel and be done with it, even if you only have the electrician run four 20A circuits.

Heck, both my wife and I work in our shop, but even simultaneously it's rare that we fire up the bigger tools when the other person is in there, if only because when we're in there we're being kinda social, so it's band saw and mini-mill at the same time, not router table + dust collector and track saw + other dust collector. I've got 100A total to the shop, we've probably used 25A peak, that'd be lights + big router in table + shop vac as dust collector.

Re " ...the conversion from 240V to 120V in the panel…", if they're in the same building, you'll run 4 conductors from your main panel: 2 hot, one for each leg of, 1 neutral, 1 ground. 120 is just one of the hot legs and the neutral. 220 is both hots (and usually you run the neutral and ground too).

And a warning: I planned out the electrical for my shop to put a socket assembly on each leg of a shared neutral circuit in each box. So at each outlet I have 4 sockets, 2 on one circuit, 2 on the other. I thought I'd be able to run fewer wires, save a little money. However… all of your sockets will need to be GFCI protected, and the shared neutral means I had to run GFCI breakers, rather than using a GFCI socket and hanging the rest of the circuit off the socket. Dang, those GFCI breakers are pricey.


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## oldnovice

A lot depends on how many *tools will be operating simultaneously*. You can assume that the dust collection system will be running for whatever other power may be used and you HVAC system.

Dust Collection + power tool(s) + HVAC = power required, solve one formula for 110 and another for 220

I do not have enough power in my garage but I work around it.
----VAC--Amps-Services

220…...30…......1
120…...20…......2
120…...15…......4
As you can see, very under powered!


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## RogerM

Rob - Panels do not cost a lot of money but it does cost a lot of money to upgrade one. A 200 amp panel will probably more than meet all of your needs and there will be room for more breakers and circuits should need them in the future. I have a 200 amp breaker in my shop which works fine and gives me a lot of confidence that should I need additional circuits in the future it will be a simple matter of adding a breaker and stringing some wire. Don't skimp on this, the bigger capacity breaker panels gives one a lot of peace-of-mind.


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## oldnovice

+1 RogerM


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## Racer2007

start at 200 amps and work up from there.


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## intelligen

Aww, man, just when I thought I was starting to get a handle on this and thought 60A might be enough and 100A would leave me room to expand, 3 of you guys come and say 200A. It's still at least a couple months down the road, but I'll keep watching for more recommendations here, then I'll get a bunch of different quotes and will report back.


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## oxyoke

60amps will work fine 100amp will give plenty of space to expand your not running a production shop.Half of a 1 stall garage,


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## DanLyke

Yeah. The big issue with 100A vs 200A that everyone's glossing over here is that, depending on the length of the run from your panel to your sub panel, you may end up with cables big enough that you have to scale up connectors, and…

Unless you're regularly arc welding while running Klieg lights for filming the process, 60A will be fine and a 100A panel will give you room to run new circuits.


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## teejk

You still have to feed the subpanel from your main panel on a breaker. Dunno if you can find a 200a breaker to fit your main panel and a good inspector will certainly check your wire size for the rating of the box (cost wise I don't think you are going to like the answer). The advice above on simultaneous use is your key IMHO. I ran 100a to my shop and everything runs just great with 16 slots to spare.


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## kelvancra

While I'm out in the shop, I have the following running:

- lights at 20 amps
- radio at 3 amps
- table saw at 15 (220)
- dust collector at 15 (220)
- heat/air at 100 (220)
- a friend using the miter and vac at the same time I'm running the saw….. 15+
- the battery charger for the lights that got left on…....

Maybe you don't need heat, or as much heat. Maybe you're just running a 1-1/2 hp collector. Maybe you don't need as much light. However, even if you count these things, considering the list above, you could be pushing the hundred limit hard and, certainly, you'd push a 60 amp circuit.

Finally, it isn't just about the amps. Each item you run at 220 to lower the amps still needs two slots.

If 100amps is you can get, you just have to deal with the fact, like the rest of use have at one time or another. When I taped my main box for a 60 amp sub, I got by running my cabinet saw, lights, radio and dust collection. Of course, I was burning my scraps for heat.

As someone said, upgrading will be a bear. If you are going for the end all now, get er done.

Just because you have a 200 amp panel does not mean you have to fill it. You can always add conduit later, but if you're going for it….........
__

My ceiling has several 15 amp outlets ran off two three-way switches for lights. If one goes out, you've still got another.

There is also a motion sensor to a third lighting circuit, since the wife parks in one of the bays during the winter and has to come into and through the shop to get out.

I have motion lights around the exterior that run too.

EVERY 120V box for tools is 12 gauge (so 20 amp).

I have a dedicated 20 amp (120v) on each wall to run the small (1-1/2hp) dust collector, so it doesn't end up sharing a circuit with something else running, like the Bosch miter, the 1-1/2 hp bandsaw, the PC on the router table).

I have several 20 amp ceiling outlets for anything from the bandsaw (it may get rewired to 240) to hand sanders or routers.

All the wall outlets leap frog so two things can run side by side and not take the circuit down/

I have a couple dedicated 30 amp (10 gauge) boxes in the ceiling, for the table saw and the three horse collector.


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## cooksmtn

I believe the difference in cost between panels of 60A to 200A will be small compared to the difference in the cost of the wire from the main panel (which I think he said is at the other end of the house) to the sub.


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## Grandpa

I use a 100 amp panel and have plenty of room and power. I have a 4 hp unisaw, 5 hp dust collector and various other smaller machines and tools. That is more than adequate. I have a dedicated welding breaker on it also. That is all you need.


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## Kennyl

Rob
Each 220 machine you have has to have a dedicated circuit.Good advice about 20 amp 120 volt circuits do not bother with 15 amp circuits.Plan your shop for more electrical capacity than you currently need.What are you running sub panel from,once your shop is built do consult with an electrician.I have 200 amp panel with 100 amp going to my pole barn and my wood shop is in my basement.My brother inlaw is a master electrician so I refer to him how to make sure I am up to code.


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## wapakfred

I don't believe that's true about the dedicated 240V circuit to each tool. They can be daisy chained much like a 120V circuit, hence multiple outlets (and multiple tools) on each circuit.


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## ScottStewart

I went through this 4 years ago. The big cost differentials are in the cost of the breaker that goes in your main panel and the cost of the cable that runs from the main to the sub. I was able to run aluminum SER to the sub, but you have to be careful with aluminum wiring. I had an electrician friend come out and supervise/show me how to make the connections and make sure I was doing that part correctly. For me the sweet spot was at a 100 amp sub, YMMV. I have plenty of extra space now in case I want to add a heater or big compressor. I added 1 240v receptacle when I did the wiring even though at the time I didn't have any 240V tools. (now I do and it was nice to be able to change a plug and go.)

Answers to your questions…
1. If you are going to have an electrician do this (and it's always a good idea), labor will be significant compared to material cost. That suggests going with a slightly larger panel than needed. As long as you trust your electrician, he/she will be your best source on what size panel is right.

2. All 120V branch circuits should be 20A. You shouldn't run a circuit regularly at more than 80% of what it is rated at, so that gives you 16A of continuous power.

3. I would put 1-2 receptacles on each wall circuit depending on what I thought I was going to run. I set up 2 receptacles on my ceiling for multiple sets of plug in lights.


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## GT350

For your size of shop the 100 amp panel should be more than enough depending on what type of furnace you are running. I have a 700 sq. ft shop running on a 100 amp panel and have never had a problem. My two ceiling mounted dust collectors and nine 2 tube 4' flourescent fixtures are on one circuit. Most of my equipment is 110v except for my air compressor and air conditioner. I have a tablesaw, jointer, planer, drill press, shaper, lathe, glass bead cabinet, stationary belt disc sander, mig welder, air conditioner, air compressor, gas furnace and misc. small power tools. Keep in mind that you can only usually use one power tool at a time, so once you add your heating or ac, dust collection, lighting and possibly the air compressor you are only going to use one other tool. If your panel is 100 amps that is really 200 amps at 110v.
Mike


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## kelvancra

I agree a hundred amp service will be adequate for most small shops, but panel capability is determined as much by the main [sub panel] breaker as by the box.

As has been said, repeatedly, you can only use so much equipment at one time (e.g., heat, light, compressor, saw, dust collector, chargers), ask yourself if you will always be the only one in the shop. I enjoy having someone else around from time to time, which might add, if only for a moment, a miter box, a belt sander, etc.

If you install a larger box, you don't have to put in a 200 amp breaker, but you can break up your outlets more, dedicate a 220 line easier and so forth.

As for more than one item on a 220 circuit, that may or may not be a problem. Even with ten gauge, that gives you thirty amps and if you were running a cabinet saw and a collector and a friend fired up the band saw, that could push harder than you want (and justifies magnetic starters so the equipment doesn't come back on with the resetting of the breaker). If you were running 12 gauge for a 20 amp circuit, a collector and a cabinet saw would push the circuit pretty hard.


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## exelectrician

@charlesA - Ha Ha Ha
@oxyolk - You nailed it.

In the very near future lighting loads will shrink to very low Amps because of LED's

Put a 20 Amp breaker feeding each and every outlet!!! 
That is one 12-2 cable per outlet!!! 
Trust me you will not regret doing this, wire is cheap breakers are cheap, Frustration resetting breakers - you put a your price on that one.

I speak from experience - why? Because I have done none of the above, and I should know better!


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## GT350

Keep in mind that when you say one breaker per outlet that in a garage you are required to have GFCI on each 110v outlet. GFCI breakers and outlets do start to add a lot to the cost when you add several outlets. Don't get me wrong I do agree with more circuits but it depends on what the budget is and if this is a permitted job or not. The other factor to consider is how difficult is it to add another circuit later on if you find out that you are blowing breakers.
Mike


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## DanLyke

GT350, you're required to have GFCI on each circuit that has multiple outlets (you can do a single-outlet without GFCI, as you might to a dedicated freezer), but you can do that with one GFCI outlet and chaining the rest of the outlets off of that one GFCI.

You just can't do that with a shared neutral (aka "Edison") circuit. For that you need something that measures the current across both hot legs and the neutral, and that's the $80 circuit breaker. Rather than the $12 GFCI socket.

Oh, and I'm not nearly as dogmatic as exelectrician about one breaker per circuit, but for the love of all that's holy don't ever put anything but lighting on your lighting circuits. It sucks to blow the circuit and be left in the dark.


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## GT350

I haven't had to do any code classes in quite some time but I believe in a garage any 110v outlet has to have GFCI doesn't it? I think that what you are talking about is like a permanent piece of equipment such as a microwave mounted above a stove.

You and I are talking about the same thing when you said chaining them together , maybe instead of 1 circuit for each outlet you have 1 circuit for two outlets, depending on what you plan on running, that just cut the GFCI costs in half. If the budget is not a concern and you have enough breaker spaces then by all means 1 circuit per outlet in a shop would be best.


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## DanLyke

Whoops! I believe you are correct, a web search suggests that as of the 2008 revisions there is now no exception for GFCI circuits in the garage! (Which is interesting, 'cause I had an electrician run 110v washer and dryer circuits in my garage in 2008 and neither of those is GFCI protected, and I know they were inspected. Maybe the code hadn't filtered down that far yet.) I stand corrected. (And, anyone with a freezer or fridge in the garage would probably do well to get an alarm for it!)


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## jimmyb

I put in a 40amp sub panel with two 15 amp circuits and one 20 amp. You are not going to run ALL your tools at the same time. I run a fan continually and have the vacuum on its own circuit. The 20 amp handles the big tools (one at a time)


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## Hybridwoodworker

In a previous life I was an electrician. A 200a panel will be a waste of money even with a heat pump running. Several lighting circuits so that if a tool fails and trips a breaker you are not in the dark. Outlets should all be 20A and use high grade outlets. Single circuits for TS, DC, Air compressor and HVAC. In my shop I have a quad outlet box every 8 feet on the wall, 2 circuits for each side of the shop with one outlet on each box on one of the 2 circuits. I have a shop vac that I use as a filtered air blower. The very most I have running at one time is the shop vac, DC and one other tool. The TS is probably the highest amperage of the other tools. In this equation, lights are of little impact. Mine are all CFL and as they burn out I will switch to LEDs.

So what you need to calculate is the HVAC, TS and DC. Please remember that the amperage or wattage listed on the nameplate is the maximum that it would draw, not necessarily the running current. If you have leaky air 
Lines then it wouldbe possible to have it run at the same time as everything else. Mine are very tight so I do not figure this in.

BRuce


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## kelvancra

My HVAC calls for a sixty on the furnace and a forty on the pump. He probably doesn't have that concern, but that wouldn't leave a lot on a 100 amp panel. Add my cabinet saw, collector. . . .

All that said, it sounds more and more like a hundred amps would be fine for this needs.


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## MoshupTrail

No worries. I have a single 20A circuit in a 3-car garage. Lights are on something else. Obviously for safety reasons I don't run more than one thing at a time. But when I run a planer or jointer, I have the vac going to collect the bits. Even that doesn't pop the breaker unless the tool bogs down. Not recommending this, just sayin'. If you have 2 or 3 circuits it should be more than enough. Oh yes, if I need to run an electric heater in the winter I just shut it off when I'm using vac to collect chips. Otherwise the single 20A circuit works.


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## Grandpa

I use a separate breaker for each 22V receptacle. I have half my lights on one circuit and half on a second circuit. I have a 110V breaker for each wall of my shop. I work by myself most of the time. I have had no problems with breakers tripping. I use a Square D 100 amp panel. The 220 breakers eat your space as other have said. I have 220V dust collector, unisaw, air compressor, planer and welder receptacles. As you can see that alone is 10 spaces. Then I have the 4 wall and 2 lights. I also added a new room and have some 110 over there. It just takes space.


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## KS_Sparky

Most everyone is steering you in the right direction. I'm curious, what size is the service for your home? Are there empty spaces or spare breakers in your panel? The answers to these questions may limit your options without further upgrades.


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## intelligen

I've been working on clearing out the garage and finally had the electrician come last week and got the quote today. After everyone was talking 200 or 400 amps in the main panel, I thought maybe I was misreading my main breaker and thought I had plenty of room to grow. But as it turns out, I've only got 100A service in the main panel! The electrician said they can only get 60A to the subpanel, but based on what most of you have said, I think that will be enough for me to get by in my small 1-car garage shop. At most I'll be running the table saw, dust collector/shop vac, air compressor, and either a window A/C or a space heater. Even with all that I should have a little breathing room, and it should be pretty rare that I'm running everything simultaneously.

Here's the breakdown in case anyone else is curious…although I'm sure prices can vary wildly by region:

1. Install and furnish a 60A sub panel in garage. $655.00 
2. Install and furnish 4 20A 120V receptacles in garage. $355.00 
3. Install and furnish 2 20A 220V receptacles in garage. $175.00

To me the quote doesn't seem very detailed, but it sounds like they'll just ask where I want the outlets when they come to do the work. I did email them asking a couple more questions though and the 120V receptacles are 2 per circuit.

I had also wanted a dedicated lighting circuit, but I guess the 60A panel is already full so I'll have to figure something else out. Maybe I'll just put the lights on the existing garage circuit.

I'm tempted to ask for a quote to upgrade the main wiring along with running 100A to the garage, but the most practical solution is probably to move to a house that already has a 100A subpanel in a bigger, heated garage.


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## DanLyke

Seems totally reasonable price-wise, probably based on running surface conduit for your sockets. You might want to clarify on the "where" with them, it's easy to run conduit along the wall where the panel is, harder to run it to the opposite wall.

And, yeah, the lights on the existing garage circuit is fine: Modern lighting is taking less and less power all the time; I think code says 1 lighting circuit per about 800 square feet habitable (garages are weird in that calculation), and between the CFLs and LEDs, I could turn on every single light fixture in my house and I don't think I'd break an amp and a half. It's just that when the router inevitably bogs down and you blow the breaker, you don't want to have to find the panel in the dark.


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## shawnmasterson

First of all running a machine on 240 doesn't mean it uses less amps. Thats a myth. you are just drawing it from 2 places instead of 1, allowing you to use smaller wire. "amps x volts = watts" Power is power whether it's 120 or 240.

Second of all you can set any size panel you want, but you will never draw more amps than you have coming into the house. So if you have 100 amp service thats all you will ever get. Setting a larger panel will allow more breaker spots, but thats all.

Third is just my opinion. A 100 amp panel should do all you will ever need, and setting a sub panel is the smart way to go. Personally I am not a fan of conduit running all over. I like everything in the wall, it justs looks and stays cleaner.

I have a 60 amp panel in my shop. I wish I had more room. On 240V I have a 3hp TS, a 3hp DC, a 2hp jointer, a 5hp compressor, and a 10hp RPC (rotary phase converter) for my 5hp 20" planer they run together. I have the 120V 20 amp outlet split half and half, and the light on their own circuit. With the lights on I have run the DC, planer, TS, and the jointer all at the same time. I was making trim and it was easier to leave the machines running then start and stop. I have never blew a breaker in 7 years. For the service wire I use #4 aluminum with ground. To those that are sneering at the thought of aluminum wire take a look at the wire from the pole to the house, Yup it aluminum and probably #4. I have my machines paired based on what they are and how they are used. The DC and compressor (30 amp circuit), the jointer and TS (30 amp circuit), finally the RPC and planer (50 amp circuit) witch also services the welder when needed.


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## Hybridwoodworker

Shawn, I Agee with your assessment and you are correct there is nothing wrong with aluminum for sub panels and even ranges. I don't like to use it for dryers or 15/20 amp circuits. With today's allot terminals, there is not the issues there was 40 years ago.

BRuce


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## cutworm

I'd get a meter base installed with a 200 amp service. Doesn't cost much more and leaves you with lots of options. You could add water heater, heat pump, big honking compressor, etc. I would suggest that you not install any 15a circuits. 
One of the problems I see on here often is someone having trouble with their TS tripping the breaker. Probably because of the feeder size and length going to their shop. To me it's also a safety issue too. Saws lose hp and stall or kickback.
A good rule of thumb - if a wire is ran more than 50' you probably want to increase the size.
I'd put the dust collector and air compressor on a separate circuits.


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## intelligen

Shawn, good advice. If you're running all that on 60A, I'm pretty sure I can run my little shop on 60A!

I didn't realize you could run 240V on shared circuits…I thought I read somewhere that 240V circuits had to be dedicated, but maybe that was just someone's recommendation.

I'm not sure I follow your argument about amps. Power is measured in watts, and if the wattage is to remain consistent, the "amps x volts = watts" equation mathematically requires you to draw less amperage if you're running at higher voltage. For example: 120V x 20A = 240V x 10A

But if you look at a 120V saw and a 240V saw, they might just happen to draw about same number of amps because the 240V one has a more powerful motor (e.g., 1.5hp vs. 3hp; 1hp ~ 746W). Is that what you were getting at?


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## intelligen

Cutworm, do you mean get a new meter and panel in the garage, or do you mean upgrade the main panel in my house so I can put a bigger subpanel in the garage?

When I measured, I came up with 70-80ft from the main panel to the new subpanel. I know code requires thicker cables for longer cable runs. I'm pretty sure the electrician will stick to code, so I should be safe there.


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## shawnmasterson

I am using #4 aluminum from the house to the detached garage (shop). If I remember right I have around 125' of wire. I don't know if I said this before but I advise you to use at least a 100 amp panel with 20 or more breaker slots. So you don't have to share 240V circuits. I am not sure it is legal by code to share outlets for 240V machines. As long as the wire is sized to match the breaker then I don't really see a problem. I am not a sparky, but I do have an understanding of electric.

If you look in your panel there are 2 "hot wires coming in from the pole". 1 is the 120v A phase and 1 is the 120v B phase. you need a hot leg from each one to make 240V. if you have a machine drawing 20 amps on 120V it is drawing it from 1 phase. If you have the same machine drawing 10 amps on 240V it is drawing 10 from the A phase and 10 from the B phase.

The easiest motor for me to read the name plate on is a 1.5 HP 3450 rpm Baldor motor. It was on the shelf. 
It states at 115V it draws 13.2 amps. 
next it states 230V it draws 6.6 amps.

"amps x volts = watts"

13.2×115 = 1518

6.6 x 230 = 1518

no matter what you do it will draw the same amperage total.


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## intelligen

Sean, thanks for the explanation. What was confusing me was your statement, "no matter what you do it will draw the same amperage total," because to me it implies that you're drawing 13.2A @230V, despite the fact that you already illustrated that you're drawing 6.6A @230V. I think it just comes down to a matter of interpretation.

One interpretation says at 115V, the motor draws 13.2A on the hot wire and returns 13.2A on the neutral wire. At 230V, the motor draws 6.6A on the A leg and returns 6.6A on the B leg (both hot, but 180 degrees out of phase). So you have 6.6A x 230V = 1518W.

A different interpretation of the 230V case is that you're drawing 6.6A on the A leg and "drawing" 6.6A (180 degrees out of phase) on the B leg. If you go with this interpretation, you have to maintain that each leg is running at 115V even though the differential between the two legs is 230V. This is the part that wasn't obvious to me at first in your explanation. In this case, you have (6.6A x 115V) + (6.6A x 115V) = 1518W or, more closely to how you describe it, (6.6A x 2) x 115V = 1518W.

So I would clarify your statement, "no matter what you do it will draw the same amperage total," to read, "no matter what you do do it will draw the same amperage total across the hot 120V legs."


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## shawnmasterson

The more in depth explanation you made is exactly what I was aiming for. I am not the most well spoken person. I know what I am saying, but I can't always say it right. You got it though. As long as you understand that going to 220v doesn't mean you are using less power then thats where I was going. So If it helped then great, if not then sorry I couldn't be more help.


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