Electricity for shop

Messages
1,456
Location
Central (upstate) NY
After figuring out the maximum load I plan to run at one time, how much extra should I add for what amperage sub panel to put in my new shop? The main house is 125 amp service, and I want to figure out if I really need a service upgrade.

Thanks!
 
Oh, my. Most houses today have a 200 amp service, at least out here. All electric houses with AC can consume lots of electrons at one time. Even a non-all electric house has a greater constant load than we realize. I would want a 100 amp box for the shop if I could get it. Running a TS with dust collector, with overhead dust filter, lights, and an air compressor that can come on automatically presents quite a load in and of itself. If the house had 200 amp, running a sub panel for 100 amp might be doable.

I can feed my shop trailer a 50 amp service. And I have to shift the motorhome to its generator to do that. I cannot allow the air compressor to be on unless it is the only thing I am using. I have to be careful running the TS or any other tool with DC and air filtering. The lights are all CFL's but divided into two circuits.

You are wise to add up your loads, but it can be a daunting task.
 
Carol, are most of your big tools wired for 120 or 240? I have mine wired for 240 already and it halves the amp draw. This, was partly to me never getting around to running a sub panel to the attached garage at the old house and using temporary wiring from the dryer outlet.

My compressor only gets turned on when I need it. I don't use air often enough to justify the energy cost of leaving it on auto.

The stove, dryer, hot water and furnace are gas. Speaking of, I need to reelectrify the furnace, as the romex to it was cut.
 
The TS and the lathe are 220v. I had considered a bigger compressor at 220v but I am trying to downsize. Because the shop is now in a 24' cargo trailer I have had to make some defining decisions with regard to tools. I just finished the outlet wiring for both 110v and 220v. Lights are next but a move is coming up first. BTW, I have not in the past intentionally left the air on auto when not in the shop, but I do turn it on and work on something else while it fills the tank. That's where I have flipped breakers in the past. This new set-up will be educational. To say the least! LOL!
 
Mark, my house is 100 amp service.

My machines are wired for 120, although I have one 220 line out there.(I run the TS off it with the DC)

Forgetting about the costs, filing for a 200 amp service upgrade for me, was not a can of worms I cared to open.(my village frowns upon people working in their garage, so I decided no inspectors for me)

My house was built in 1948, finished in 49 or 50, and from what my local electrician told me when he put in the other lines, they don't permit homes in my village to upgrade, unless its a commercial business.
whatever, my point is that Ive been operating like this with full equipment since nov 2008, and yes, I blow fuses now and then, mostly in the summer with AC's running, but if I keep as much off in the house as possible, I have little problems.

Id love to put in a larger jointer and planer, but I don't have the juice.

you can run your shop on 120 power.
 
Allen is giving great advice. The secret is load management, don't try and run everything at once. The other thing is that your 220 service provides 2 110 circuits sharing a common neutral to the main lines. You need to be wired so you run off both sides of this. That is where many garage shops suffer. They have 1 110 line servicing the garage shop. You need at least 2 circuits and need to try and split your tools running at the same time between them. If you have a 110 dust collector that will be running when your table saw runs it may also run when your planer runs and your sander runs ect. But your TS and lathe or planer sander ect won't likely run at the same time. So your Ts, sander. lathe, planer ect can share a circuit as they will usually trun one at a time and you can make sure they do. So they can be on one circuit while your dust collector would be on another circuit and should be on the other side of the service line as well. Probably a good idea if you have a compressor it could share a line with the Dust collector. When the clothes dryer is running or an electric range is being used just do some hand work or clean up. And the other thing is if you can run tools off 220 they always run more efficiently off of 220 than they do 110. The current is cut in half and that cuts down on the line losses. Not that you can't run off 110 and I do except for my Air Compressor but if I was wiring from scratch it would be 220 all the way.

Garry
 
Last edited:
Mark, sounds like you're on the right track adding up all the scenarios of things that may run at the same time (lights/TS/DC, lights/compressor, lights/lathe/DC, etc...).

If you were upgrading service at the house, I'd go with 200 amp at the house and 100 amp to the shop. If you're looking to stick with 125 amp at the house I'd still consider a 100 amp in the shop if you have room and code will allow. Now you may throw the main at the house if you have too much running between the two locations, but you'll learn when you can/can't draw more power. My thought is that you're paying for the service to the shop once and don't have to upgrade it again if you decide to replace the house with a 200 amp later.

EDIT: I asked one of our electricians here at work. He said that your sub-panel size will depend on the rating of the breaker tab size of your existing main panel. The tab is the part that the breakers clip onto when snapped on to the main lug. It should list what the maximum size of breaker it will support, some older ones have a max of 70, but most newer ones are rated up to 100 amps or more. Check that and it will narrow down what you can do if you're going to use the existing main.
 
Last edited:
Darren, great minds and all that. I'd decided to put in a 100 amp main breaker with 100 amp capable cable, but then put a smaller breaker supplying the shop from the service main. This way I don't take out the house, but am ready to go if I do upgrade service later.

Now time for some code book reading and researching.

Is it silly to get a box that uses breakers in common with the house service main? That takes Murray breakers available at Lowe's. I think thelabel says QP but I have to check.
 
Darren, great minds and all that. I'd decided to put in a 100 amp main breaker with 100 amp capable cable, but then put a smaller breaker supplying the shop from the service main. This way I don't take out the house, but am ready to go if I do upgrade service later.

Now time for some code book reading and researching.

Is it silly to get a box that uses breakers in common with the house service main? That takes Murray breakers available at Lowe's. I think thelabel says QP but I have to check.

Nope, not silly at all, good to have a place to get spares in a pinch and don't have to remember what brand you need to get for one vs. the other.
 
Carol, are most of your big tools wired for 120 or 240? I have mine wired for 240 already and it halves the amp draw.

Not exactly, you are effectively drawing half the amps on each leg - but you end up with about the same amp draw overall (i.e. you're drawing 2 * 5 amps instead of 1 * 10 amps). The motor might be slightly more efficient and there might be a smidge less loss but in the grand scheme of things its not really meaningfull (at our scales).

As to your original question - agree that the best way to answer that is to sit down and add up all of your actual load. If you can get a clamp on ammeter that will remove a lot of the guessing from that process, especially if you can get one that can log load over a period of time or at least peak loads. Its worth checking what the burst load is when tools/etc.. turn on as pretty much all electrical equipment takes a lot more power on turn-on than under continuous load.
 
Not exactly, you are effectively drawing half the amps on each leg - but you end up with about the same amp draw overall (i.e. you're drawing 2 * 5 amps instead of 1 * 10 amps). The motor might be slightly more efficient and there might be a smidge less loss but in the grand scheme of things its not really meaningfull (at our scales).

As to your original question - agree that the best way to answer that is to sit down and add up all of your actual load. If you can get a clamp on ammeter that will remove a lot of the guessing from that process, especially if you can get one that can log load over a period of time or at least peak loads. Its worth checking what the burst load is when tools/etc.. turn on as pretty much all electrical equipment takes a lot more power on turn-on than under continuous load.

Sadly, Ryan, almost all of my tailed tools are in the new home already, which is currently completely devoid of 220 and has perhaps one 120 outlet. I'll have to go by whatever lies are on the motor faceplates.
 
Everyone always wants to say there is no real advantage but with any heavy appliance or tool the advantage is significent. That's why you won't see many driers or ranges, air conditioners ect running on 110. You can't change physics.... The only reason any of this stuff is on 110 is for convience becausethat the plugins most of us have.

Sent from my GT-P5113 using Tapatalk 4
 
I'm about to start looking things up for amp draw. For kicks and giggles, my 220 stuff is a 12" RAS, 6" jointer, 60 gallon air compressor, and I guess that is it (I do have a DC, but plan to upgrade to an Oneida cyclone so will get that from the website).

What do we think the current draw order is going to be? Which tool needs the most, etc?
 
I'd bet a large doughnut on the air compressor and the new cyclone fighting it out for top honors - which will win depends on the specifics of them.

I'm seeing ~15-20amps for compressors in that size (peak)
and 12-20 amps for the oneidas (depending on the model)

Those are both "peak" numbers. I would expect the compressor to actually draw something pretty close say (waves hands) 80% of peak it when its running (after the startup surge). The DC will vary somewhat depending on how much airflow you let it have, the more air the more amps (and the more air to.. so.. yep).

Both the jointer and the RAS should be somewhat lower - random guess at the 7-10 amp range each, but could be wildly off :D I'd bet that the jointer takes more in real load while its running but may well be rated about the same.
 
The other thing you need to look at in order to get a fairly accurate idea of your amperage requirements is how many watts are being consumed. The current coming in is rated in volts and amps but the actual load on the panel is in wattage. The motor on my Craftsman planer is rated at 12 amps / 120v. Volts x amps = watts, so if I use those numbers my planer at peak power should be consuming about 1440 watts. For DC on the planer I use an old Rockwell vacuum that just so happens to also be rated at 12a / 120v so with the two running at the same time they are consuming 2880 watts. I also have to consider my lighting load which would include my radio running in the background. The general rule of thumb for figuring light load wattage for a house is 3 amps per square foot. My shop is rough 240 sf so I'll just round that load up to 700 watts. My total load with these items in operation is 3580 watts. I know that the feed into my shop is 240 volts, that is 120 on each leg of the panel so to find my required amperage I divide 3580 watts by 240 volts which means I am drawing roughly 15 amps to run my planer and vacuum at the same time. I learned this from an old electrician friend of mine a few years back when I was helping him do some house wiring but a quick google search will also give a lot of info for calculating panel load requirements.
 
How do you know your 120 stuff is going to balance out on opposite legs? If you happen to plug two things into the same circuit, isn't that just going to be on the same leg?

Practically speaking at the draw any of most of our tools have I'd say almost no one worries about it (some commercial apps or if you only have say 20 or 40 amps total on the shop extension it would be a concern I suppose).

Yes it will be on the same leg (on the same breaker even so yes :D).

I actually replaced a bunch of the outlets in my shop with different colored outlets coded on the circuit they were on so I could easily see at a glance what circuit anything was getting plugged into. That obviously doesn't help the leg balancing problem very much though - although if you also made sure to alternate legs it could help as long as you paid attention to what you plugged in where. This allows me to have the router on one circuit and the vacuum on another just by plugging into adjacent but different circuits (actually I stole the garage door circuit for the DC as I never run it and the door up/down at the same time but the idea holds).
 
How do you know your 120 stuff is going to balance out on opposite legs? If you happen to plug two things into the same circuit, isn't that just going to be on the same leg?

I have a pretty small (13' x 18') shop so I am powering it with a 60 amp sub panel from the house. I have a 115 amp circuit that runs the lights and I have two 20 amp circuits, one down each side of the shop with 4 outlets on each line. Each of the 20 amp circuits is on a different leg of the buzz bar so that makes it pretty easy for me to split things up. I never have more than two things and lights running at the same time and I'm not kicking out breakers or losing power so the amp draw has never been a real issue.
 
More planning. My 120 general purpose lines are going to need GFCI. I'm thinking to use GFCI breakers so I can install an excessive amount of receptacles if I want and not break the bank. GFCI is not required for the 220 receptacles, I don't think, need to review. If the two pole circuits do not require ground fault, should I install them anyway?
 
+1 on the GCFI breakers, it makes the rest of the run straight forward. The downside is that they cost more than outlets - about twice as much (only the first outlet in a chain needs to be gfci) and you have to walk back to the panel to reset it.

Its rare to see GFCI 220, in at least most old versions of the code they weren't explicitly required but the verbiage is somewhat vague so I think some areas may have different ideas. I'd ask the local inspector/authority since that's what will matter when you have it inspected (or go to sell the place eventually anyway). If you're on a conductive floor (concrete, dirt, etc...) or worried about water intrusion anywhere ever its also a reasonable safety precaution. The possible downside is that some tools can cause nuisance trips and they are eye poppingly expensive.
 
Top