Planning circuits- 240/120

[Alex Stace]

I am planning wiring my shop project. I currently do not have any 240 tools but anticipate getting some soon.

From my quick look at grizzly etc it appears most of them are 15 Amp 240v for which 12 gauge wire would be acceptable.

Now are any of them typically actually 120/240 like some washers etc where they would need 12/3 wire for a neutral for the 120 portion IE 4 prong plug vs 3 prong?

(trying to decide if I should run 12/2 or 12/3 to every box)

[Steve Meliza]

I'm sure some machine somewhere out there needs the neutral, but I don't think you'll run into it with homeowner level WW machines. At least one person around here is going to tell you to run 12/3 everywhere and at each box put in a 240 and a 120 outlet. That works, but if you price out 12/2 and 12/3 you'll see that 250' of 12/2 is about $65 but 12/3 will cost you around $117 for that same 250'. Personally I'd rather have two runs of 12/2 than one of 12/3.

[Art Mann]

I have only seen 240VAC with neutral and ground in one piece of woodworking equipment. It was a drum sander with a 240V sanding motor and a much smaller variable speed conveyor motor.

[roger wiegand]

If you're wiring from scratch I think it makes sense to use multi-wire branch circuits everywhere, pulling 12/3 w/g. At each box you can have both 240 and 120 v outlets, you can even split the 120 duplex outlets so that each of the duplex outlets is on a different side of the MWBC. This provides enormous flexibility in your layout. You then only need to really plan for machines that need more than 20A/240V, which are not many for hobby level shops that will require heavier, probably dedicated wiring. That said, I have given my bigger machines that are in a permanently fixed location or that might operate simultaneously with another heavy draw (table saw, compressor, dust collector) dedicated circuits, typically 12/2 w/g, but heavier for motors over 3 hp.

[roger wiegand]

I'm sure some machine somewhere out there needs the neutral, but I don't think you'll run into it with homeowner level WW machines. At least one person around here is going to tell you to run 12/3 everywhere and at each box put in a 240 and a 120 outlet. That works, but if you price out 12/2 and 12/3 you'll see that 250' of 12/2 is about $65 but 12/3 will cost you around $117 for that same 250'. Personally I'd rather have two runs of 12/2 than one of 12/3.

I think the point of a MWBC is that it does give you the equivalent of two 12/2 120 v runs for both lower wire cost and much lower installation cost as long as 12/3 costs less that twice as much as 12/2, which it always has in my experience.

[Mike Henderson]

Someone correct me if this is wrong.

It seems to me that if you run 12/3 to each box and put in a 240V and a 120V outlet, you could have problems if you want to use both of them at the same time. Let's say that you hook up a 240V tool that requires a 20 amp breaker. And your 120V outlet is rated at 15 amps.

This is assuming that you connect the black and red for the 240V outlet, and the black and white (or red and white) for the 120V outlet.

If I put in a double 20 amp breaker, which is what would be called for by the 12 gauge wire, and I'm using the 120V outlet drawing let's say 10 amps - and then I turn on my 240V tool, I'm going to trip the breaker (actually, one side of the breakers but it will trip both sides because they're tied together).

So what am I missing? Did I misunderstand how this would be wired? Seems that it would be better to run separate circuits for each voltage.

Mike

[And if the idea is to wire the outlet either for 240V or 120V, depending on what tool you have, then you give up your 120V outlets at that location when you connect the 240V tool.]

[Alex Stace]

It appears the cost would be close
12/3 wire is about 5% cheaper then two runs of 12/2 $115/250 vs $63/250 locally. Initial Breaker cost would be slightly but negligibly higher.

Now what do most folks do for spacing 4 feet?

[Duane Meadows]

Your absolutely right, Mike. The circuit is still only good for one major machine at a time. Perhaps 2 120V, provided they are on opposite legs of the 240V circuit. I would much rather run individual 240V and 120V circuits.

[Marty Tippin]

I'd suggest running dedicated wiring for your 220 outlets.

And use 10/2 wire for the 220 runs even though it's bigger than you need right now - you could upgrade to a 30 amp circuit if you need it someday by just changing the breaker and outlets. 20 amp 220 will get you up to about 3hp or so, but 30 amp will do around 5hp.

I'd also run about twice as many 110 circuits as you think you need, with 2 duplex receptacles on separate circuits at each box.

[Alex Stace]

[And if the idea is to wire the outlet either for 240V or 120V, depending on what tool you have, then you give up your 120V outlets at that location when you connect the 240V tool.]

This was really my original idea, probably have every other box be a homerun that I could change out between 120 or 240 later, with the rest of the outlets as a couple of standard daisy chained 120 circuits.

I see the merit in the 10/2 wiring, that would maybe double the cost of wire, but allow for even more versatility.

My initial plan was to try and leave a wire trough in the wall with plywood facing so I could change anything later, but I have not figure out a good way of doing that without making a band of lower insulation value.

[Rod Sheridan]

You are correct, however I can only operate one machine at a time so it's not an issue..........Rod.

[Duane Meadows]

You are correct, however I can only operate one machine at a time so it's not an issue..........Rod.

As long as one of those machine isn't an air compressor that just happens to start up while you are running another machine. Also I run my DC at the same time as any number of other machines. That's why I have dedicated circuits for both of those, and keep my 240V outlets separate from my 120V stuff.

[Steve Meliza]

Now what do most folks do for spacing 4 feet?

That's what I did, but my garage has 24" o.c. studs which made the choice easy. They are also located above 50" off the floor at all points (except over the workbench) to allow leaning up of plywood and other objects without blocking the outlets, not to mention my back thanks me.

My installation is in my garage so I opted for OSB for the wall covering and mounted 1/2" metal conduit to the surface. My work area is an "L" shape so I have two runs of conduit that go the entire length of the "L", one serves a pair of general purpose 20A 120V circuits and a homerun for the fridge/freezer unit. The other conduit serves three homerun circuits that initially started as 20A 120V but when I purchased a 240V jointer one of them got changed to 240V. Since I'm using conduit I have great flexibility to make changes in the future and didn't have to fuss with drilling holes in my load bearing studs and feeding the cable through. For this type of install you buy three spools of THHN wire, green, white, and black.

Let me expand a bit on those two 20A 120V general purpose outlet circuits. Each outlet location is a 4" square box with two duplex outlets in each box. All of the duplex outlets on the left side are served from one circuit and the right side is from the other circuit. It was more work to wire up, but I can tell at a glance how my two circuits are loaded and have access to them both at every location. I do have them every 4' along the wall, but where it goes across the back of my workbench I put them every 2'. I got some comments from friends and family about the large number of outlets used, but I have never once regretted being able to find a free outlet anywhere in my work area.

[george newbury]

Definitely plan on running at least one high amp 240V outlet for future flexibility. It made a big difference to me when I found equipment on sale to know my wiring was adequate. My latest "score" was a new from Amazon Everlast Power Arc 300 AMP welder for about $260 http://www.amazon.com/EVERLAST-Power...=1419024184052 , vs the $590 it normally goes for. It sucks up to 60 amps, but a 50 amp circuit might do. I also have a planer I run off a 50 amp circuit and plans for a bunch of 3 phase equipment to be hooked up to run off a rotary phase converter on a 60 amp leg.

[Rollie Meyers]

If someone is thinking about running 12/3 NM so they can have 120 & 240 volt receptacles on that run, realize that all 120V receptacles in a garage or outbuilding require GFCI protection, depending how it's done it could get real messy, make a plan of machines you have & want & where they will be placed & wire accordingly to their power requirements.