# Shop electrical question



## g1hopper (Nov 10, 2008)

I am having a new home built and am trying to make sure I think of what I need for the shop are. The new shop will be part of an attached garage. Shop dedicated space will be about 525 sq. ft. I am considering having an electrical sub panel ran into the shop area.

Do you think this is a good idea?

How many amps should the sub panel be? The estimate I was given was for 60 amps or 100amps.

Current I have an electric heater that runs on 240v. I have to have a gas heater at the new place, but may still need an outlet for this one for a short time.
I hope to upgrade my table saw and maybe dust collector someday to 240v also.
I would like to hear your thoughts. Maybe anything else I should be thinking about while I am at it.


----------



## bigblockyeti (Sep 9, 2013)

Go with 100 amp, if you find yourself with a large planer working hard and a big dust collector working with it you could be very close to 60 amps with just those two, not to mention lighting, and everything else that's in the shop. It's a little more money now, or a whole lot later on.


----------



## 489tad (Feb 26, 2010)

Its a good idea if there's not enough room in the main. Easier to do it now. One thing I did in the event I ever converted to 220 was to have the proper gage wire installed. I never did the switch. I hope this helps.


----------



## mojapitt (Dec 31, 2011)

Always go bigger in the beginning. You will never hate yourself for it.


----------



## grazer (Jul 8, 2011)

100 amps. Better too much than too little and not a lot more money to accomplish in the building phase unless you are a long distance from the main panel. The reality is that you are never going to be utilizing all of the big amp draw equipment at once since you are not a production shop. However, what man doesn't want more?


----------



## Wes1952 (Nov 12, 2013)

Yes add the sub panel. You'll find it money well spent and a convenience that will pay you back when you make changes and upgrades later.


----------



## crank49 (Apr 7, 2010)

Yes to the sub-panel.
I am just starting to do the same thing.
Going with 100 amp because I also weld and I want enough juice to run an air conditioner.
Why limit your future?


----------



## g1hopper (Nov 10, 2008)

Thanks everyone, that is what I thought you would all say.


----------



## dhazelton (Feb 11, 2012)

Whatever you are using for heat I would see if you can add the garage as it's own zone now. May save you money down the road and be more comfortable vs. a propane space heater.


----------



## jgreiner (Oct 23, 2010)

I just had a subpanel added to my basement and I got 100amp, as everyone before the cost difference shouldn't be a huge amount, and it'll be way more expensive to upgrade to 100amp should you ever need too later.

-jeremy


----------



## todd1962 (Oct 23, 2013)

Subpanel - absolutely! If you have more than 6 circuits you'll need a main breaker.
I have 60 AMP service to mine and my shop is 16×24. I have all the tools I need and haven't run out of juice yet; however, 100 AMP would probably be a good idea. Definitely if you ever weld.

I wired my own shop. I made sure to put separate circuits for my compressor and DC. That way I can run my DC, a power tool on another circuit, and not have to worry about my compressor cycling while all of this is going on. Maybe slight overkill but I wired it myself and I had a main breaker so I could put as many circuits as I wanted.

Since your shop is attached you'll likely have to use drywall. I used OSB in my detached shop so I could mount most anything on my walls without worrying about studs. The added bonus is I don't have to worry about punching holes in the walls accidentally.


----------



## Mahdeew (Jul 24, 2013)

Yes, for sure 100 AMPS or better. Allow at least two 240 Volt runs as they are more efficient than 110/120. You can save a lot of money using a 240 volt heather (forced air) than a 120 one.


----------



## DocSavage45 (Aug 14, 2010)

Is the wiring in conduit? Not only a big panel but make sure it will accommodate the maximum load you intend to run. Make sure the draw is from both sides. Use copper not aluminum. ground faults as well.

Will you run a big dust collector and a big cabinet saw?


----------



## Whiskers (Nov 6, 2012)

Ground fault outlets are not supposed to be used on circuits that use large electric motors from what I had read, electric motors supposedly kill them.


----------



## darthford (Feb 17, 2013)

I just had a house built last year, I really wasn't planning to get back into woodworking at the time so I paid no attention to electrical in my 3 car garage in prep for this. Here's my list…

Go repeatedly cuff your electrician sub in the head until he's paying attention and taking notes then…

1. Tell him you want to conserve breaker slots for later use, I found they will waste 15 amp slots on short runs that no way will ever pull 15 amps. They focus on what easiest and quickest for them to get the job done. They will also run whacky illogical runs, they have no master plan, they give no thought to laying things out before they begin, and they don't keep track of what breaker feeds what and mark it accurately. I'm talking the general runs, obviously they do mark the big breakers correctly for oven, drier, heat pump etc.

2. There are some 15/30/15 Square D breakers that give you two 15 amp 120v breakers plus one 30 amp 240 volt breaker in the same space a single 30 amp 240 volt breaker takes up. They cost more but free up 2 breaker slots.

3. Consider your dust collector, I have this 1.5 HP Grizzly G0703 Cyclone that pulls over 60 amps on start up. The breaker will usually take that surge without tripping but I found it would still trip a 20 amp 240 volt so I ended up having a dedicated 30 amp 240 receptacle for it since it would always be running with a machine.

4. I needed another 30 amp 240 receptacle for the table saw. My bandsaw and jointer both require a 20 amp 240 volt breaker. Some 20 amp 120 volt for other tools. Factor in shop lights you can never have enough. I use 6 bulb fixtures with 6 'daylight' bulbs, awesome shop lights, I have 5 in my 3 car garage already and really could use 2-3 more. When you start adding up what these fixtures pull that will be a dedicated circuit.

5. In our area they inset the breaker panel into the wall so once its closed up with sheet rock there's no easy way to run more wire. I found I wanted to run some stuff outside the wall in conduit, but how do you get from the panel inside the wall to the surface in a way that's code. I would consult your electrician on this. I like sturdy metal boxes screwed to studs for outlets not the flexo-matic plastic junk they use these days.

6. The electrician is likely to use the cheap 10 cent china receptacles, budget $100 to $200 more to opt for the higher quality throughout the house, that's one of the dumbest things imo for the paltry increase in cost you can get a much better quality.

While I'm on that subject that's true for the rest of the house. My cost to upgrade from the junk particle board cabinet boxes and drawers to 3/4 inch hardwood plywood boxes with maple dovetail drawers was only a few hundred dollars. The upgrade from knotty alder plywood panel doors to hickory with solid raised panel doors was another no brainer upgrade price wise it wasn't that much. I did go with the plywood panel hickory doors in the baths due to the moisture. I added soft close on the kitchen drawers and doors.

Next was plumbing, the builder budgeted to install and I'm not kidding $50 China toilets. I upgraded to American Standard, they were a LOT more expensive like $250 each but worth it imo. The China builders grade toilets were junk. I didn't go hog while elsewhere, upgraded the kitchen sink to black granite composite vs the builder grade cheap stainless, went with the builder standard round white sinks in the baths, upgraded the master faucets to mid grade and the other bath faucets above the $10 builder grade, yeah $10 that's how much credit I got towards a better faucet.

Next was lighting, I was only given a $1,000 budget for lighting fixtures, I would have had to buy literally the cheapest China fixture for every location to stay within that budget. I ended up spending over $2,000. I didn't buy the fanciest fixture available, just good solid tasteful choices of good value for the money. It really made a difference. The lighting budget was way under what it should have been.

Next was flooring, again the builder budgeted for builder grade 99 cents a sqft carpet, it was horrible though I did go with that in the 2nd, 3rd, and 4th bedrooms. It was so cheap I didn't mind throwing it out later after some use. I upgraded the master and rest of the house carpet quite a bit. Go with a thicker pad also. They planned to use the snap together Pergo type flooring, I upgraded to 3/4 #2 knotty oak sanded and finished in place.

The only other upgrade was counter tops, the builder planned to use tile, I upgraded to slab granite throughout the house, its awesome.

Okay well that was quite a brain dump hope that helped.


----------



## icsparks (Sep 17, 2013)

It's a misconception that a piece of equipment wired 220v is more efficient then 120v and will save a lot on electric bills. A 5000 watt heater will still consume the same amount of energy wired at 120v as it will wired 220v. The amount of efficiency would only be in the amount of resistance in the size and length of wire used. You wouldn't see the cost savings in your electric bill in a lifetime. The real savings is the up front cost where you can use a smaller wire size at a higher voltage to do the same amount of work. Say going from a #10 wire to a #12.


----------



## Whiskers (Nov 6, 2012)

I got to weigh in on here, Charlie makes a point about a 5000w heater will use the same electricity if it on a 120v circuit or 220v, and that is true, cause the heater is rated at 5000w and you basically are billled by the watts used. Motors though are a different beasty, they are not rated in watts. 220v motors are more efficient in heavier horsepower uses, period. Im not a electrician or physicist but once worked with a bunch of them and asked what the different measures meant. Unfortunately he did not cover watts, but amps, voltage and ohms he did cover with a simple analogy. If you have a army and you need to send it over a fragile bridge (fuse) in a set amount of time, you have several options. Single line in a dead run or side bye side in marching formation for example. The speed the men run is the voltage. You can send them across as fast as you want and it wont effect the weight limit of the bridge, but in formation you can send them over slower, but might break the weight limit which is the amperage. Ohms can be thought of as the wind blowing against the soldiers impeding their progress, forming resistance, which might also put further limits to the bridge.  I believe watts is actually a math measure of both amps and volts together (soldiers moved at a time), not a single entity, so in heating terms, a 220v 5000w heater while it uses the same amount of electricity as a 120v, it is much easier on the wires cause them soldiers (electrons) are running across 2 bridges (wires) not just 1. You have to have beefier wires for 120v than 220 if your going minimalist.

One more note, wattage is a lousy way to look at heaters, actually u want to look at BTUs or something for heat output, not the amount of electricity consumed. Ideally it would put out tons of Heat and use very few watts. Using watts is bad, putting out heat (BTUs) is good.


----------



## icsparks (Sep 17, 2013)

1 HP = 746 watts A 1 hp motor pulls about 10.8 Amps wired at 120v doing the algebra, 120×10.8 = 1296 Watts when your motor is running at full load and wired on a 120 Volt electrical circuit.
Same 1 HP wired at 240v pulls 5.4 Amps doing the algebra: 240×5.4 = 1296 Watts when your motor is running at full load wired on a (nominal) 240 Volt electrical circuit.
I left out the motor nameplate power factor and motor efficiency to simplify the math but it would still work out to be the same. 
The electric meter at your house measures electricity usage in kilowatt hours (KWH). If you run a 1000W load for one hour, you've just used 1 KWH of electricity. So the motor is costing essentially exactly the same to run at either voltage level.


----------



## Whiskers (Nov 6, 2012)

So my grizz table saw with the 3hp motor would pull 32.40 amps at 120 volts, instead of its 16.2 at 240v, hmm, I wonder why it wants a 220volt circuit? On a 120volt circuit we would be popping breakers if we lucky, or hearing a snap crackle pop and my scream as i run to the phone to call the fire department. Whats your point Charlie? Im not totally sold on the concept that HP translates straight to watts though.

Your numbers are slightly flawed according to my manual, as it states the grizz saw only needs 14 amps, just looked that up


----------



## Whiskers (Nov 6, 2012)

Since me and Charlie seem to be having this peeing contest about motors and hp vs amps, I thought I would mention some observations with my favorite tool. Charlie relates HP to watts, which is directly related to amperage. Ive had this craftsman miitre saw for about 30 years, and I know it well and use it a lot. Often to use it and hook it up I pull this terrible trouble light thing down from the ceiling to plug it in. Thing is it is super sensitive. The breaker built into it is problematic. If I'm cutting 1×2s or even 2×4s that are untreated i do not usually have a problem, but if i go for anything treated or other than soft pine that trouble light is well trouble. Motors do not pull a constant amount of power based on horsepower, they do not work that way. They pull power based on the load they given. Turn them on and it takes a bit of a spike to get them going, than they will hmm happily at a low level til fed a load, than they start sucking power til bogged down and they hit a peak.

The trouble light is handy for small tools, or using the mitre saw for light weight wood, but it is proof that tools that are rated in HP do not use a uniform amount of electricity. You can not universally state a math formula of HP = amps = watts.


----------



## icsparks (Sep 17, 2013)

As I said to make the math simple I left out the power factor and motor efficicency but if you need it here it is. http://www.elec-toolbox.com/Formulas/Useful/formulas.htm
The point is that saw will use the same amount of electricity either way its wired 120v or 240v under normal conditions at the rated voltage loaded or unloaded.

I never once said that a motor will always draw the same amount of current all the time. Just that the amount of power consumed is the same no matter the voltage.

You have to use your own motors nameplate data, not all motors are = so yes the math will be off but if you use the nameplate data of you motor and do the math and use an amp probe to mesure the current draw it will be close. So to do the math right 746/120 = 6.2 amps 746/240=3.1


----------



## OldRick (Oct 6, 2013)

I would go with at least 100 amp service. In my opinion there is no such thing as too much electrical service and especially in a shop. You're already doing new construction so this is the time to spend some extra money and have safe, dependable service installed that is ready for anything that might come in the future. I also never use below 20 amp breakers and 12 gauge wire. My wife says I am an electrical snob but we never worry about what we plug in. This is definitely an area where you really want to do yourself a favor.


----------



## RogerM (Oct 31, 2011)

I am not sure what you are planning for the future but definitely put in a sub panel. Instead of a 100 amp panel though go ahead and put in a 200 amp panel for just a very small amount more. You won't regret it.


----------



## darthford (Feb 17, 2013)

RogerM agree with a 200 amp panel that's how I would go. Note in my area that would require another feed from the utility transformer. Here one transformer can feed 2 houses each with 200 amp service. Typically the houses share the cost of the transformer which can be several thousand dollars. I think the most they will let you pull into a sub panel off the 200 amp house main panel is 50 amps.


----------



## ClintSearl (Dec 8, 2011)

A sub panel only adds circuits, so if the main is a 200 amp, and can handle the total loads, a sub will be fine. Perhaps more important is the wiring and outlets. All the 120v circuits should be fitted with 20 amp breakers, 12 ga lines and with 20 amp outlets, and the 240v lines with at least 30 amp breakers and 10 ga. wiring.

I wired my shop with its own service/meter and 200 amp panel.


----------



## MrRon (Jul 9, 2009)

You can never be over-kill when it comes to electricity. Go for as much capacity as you can get. I have 200 amp service for my shop and I can run saws, compressors and welders all at the same time with no light dimming. I would consider 100 amp service as a minimum if you are not running more than 2 power consumers at a time.


----------



## crank49 (Apr 7, 2010)

Whiskers, Charlie is telling you straight up the truth.

It gets a little more complicated when you talk about different types of motors and "rated" maximum horsepower. But, every motor can be rated in watts.

In fact, in Europe they don't use horsepower at all because it is a poor way to rate power since it can be manipulated and fudged by the manufacturers. All motors in the metric system are rated by KW. Even gas and diesel engines.


----------



## Knothead62 (Apr 17, 2010)

Tell the electrician what power tools you have and their spec's. He should be able determine what you need in order to comply with NEC and local codes. Also, you should check with the utility company what their requirements are.


----------



## TaybulSawz (Oct 17, 2013)

R U Sure about that Charley?
That's Partially true but there's a lot more to the equation than just the wattage pull etc. The effect on the motor, and the wiring etc all come into play as well. Lots more needs to be considered than just the savings between the 2. That's JMHO!!!!


----------



## Grandpa (Jan 28, 2011)

Go with the largest panel you can get in your budget. If it is a sub panel it will have to have a breaker in the main panel that will be used as a main for the sub. I used a separate feed from the transformer. I used GFCI receptacles on all my 110V receptacles and have never had a motor "eat one". GFCI only measures amperage out and amperage back. When the balance is different or there is no balance then they trip. I don't have that problem and I have been in this shop 13 years. I used GFCI because it is required in garage circuits unless it is a dedicated circuit for something like a freezer or sump pump. I have a 100 amp panel for the shop and it looks like I will get it filled eventually. Go larger that you plan to need. You will need it later and it will already be there. Now is the cheapest time to do it.


----------



## g1hopper (Nov 10, 2008)

Thanks for all the info. I have found it quite interesting. I think 100 amp will be enough.


----------



## teejk (Jan 19, 2011)

I think many people would say that they notice a difference on 240v over 120v but that is probably a function of "running load". In theory it comes back to KWH and I agree that there should be no difference in the electric bill. But "load" causing the lights to dim would suggest that more "load" might cause a need for more KWH on a 120v circuit.

That's not your question is it??? I have 100a in my detached shop (24 slots in total). In a home shop environment I doubt you will ever use anywhere near that at any given time unless you have 20 hands capable of running 20 tools at once. Just IMHO.


----------



## rum (Apr 28, 2011)

+1 I wish I had a 100 amps to a subpanel instead of jamming everything into my main panel.

BUT I'd put in a 200 amp panel with 100 amp feed because the 200 amp panel usually has lots of extra breaker slots which is nice to have. A handful of 220v runs can really suck up panel space in a hurry and the cost difference between the two panels is not all that huge (compared to the rest). Something like a GE 40 slot panel would imho be perfect.


----------



## TopamaxSurvivor (May 2, 2008)

A motor will use the same power on 120 or 240, but…...... *A 5000 watt heater will still consume the same amount of energy wired at 120v as it will wired 220v.* Not really, the heater is a resistance. Under Ohm's Law, cutting the volts in half will cut the heat to 1/4 the output. The 5000 watt at 240 will become a 1250 watt at 120.


----------

