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these are general purpose 240 volt receptacles, not hard wired to a machine, that would changes things
just like 120 volt 20 amp general purpose receptacles you don't add up the outlets to size the wire, 1 outlet or 30 outlets all get 12/2 wire
this pic is a 240 volt 20 amp duplex receptacle. 2 receptacles in one box and 4 screws to wire in the next 240 volt 20 amp duplex receptacle

 

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Discussion Starter · #42 · (Edited)
Thanks to all for all the feedback. I had no idea I'd spawn a thread this long.

So for reference, my Main Panel in the house has 200 AMP service. I'd like 100 amp service for the garage, but depth seems to be the major issue. if 60 is all I can get, I'll make it work.

Ogre, the 240v 20amp service for my Unisaw at the old shop just had a single outlet. I didn't know that 240v duplex outlets were a thing... 'though I rarely mess with 240v...

I'll check the local code WRT the 240 outlets, I'm fairly sure that my city (Webster Groves, MO) adopted the national electric code.

Ideally, I'd like at least four 240 circuits out there, but I don't intend to ever use more than two 240v tools at a time (dust collector & a major tool like my Unisaw, so maybe just two would do it.

2x20 amp circuits = 40 amps in use simultaneously. 60 amp service would only give me another 20 amps to supply the rest of the shop (lighting and outlets) and I'd rather keep those on different breakers. Dang. .

When I get the panel installed, I'll get the electrician to install the 240 outlet for the compressor/welder - as the panel will be in the "car" part of the garage and I want the outlet right there anyway. Obviously, I'll have the existing circuit for lighting routered into the new panel. Until I finish clearing out the space for my shop, I don't think I'll have a clear idea of where everything needs to go.

At some point I'm also going to remove all that asphalt and put in a *level* parking/drive area, so that'll be a good time to install a deeper, "beefier" service to the garage. Hopefully I can "make do" with a 60 amp service until then.
 

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Put in a 100 AMP panel now

You can use a 100 AMP panel and supply it with the existing cable as long as there's a 60 AMP breaker in the main. A 100 AMP panel will give you more slots so you can wire in more separate 240 V circuits. Then when you can, you run a larger supply wire to the building and NOT have to change out the panel! :wink:
 

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Discussion Starter · #44 ·
Ah, cool. I was thinking that should be a possibility. Invest in a good size panel up front = making life easier down the line. I like it.

I take a kinda-similar approach when (re)wiring outlets. Run 12/2, even if the circuit is only going to be 15 amps. If necessary, you can upgrade to 20 amps later w/o rewiring.
 

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2x20 amp circuits = 40 amps in use simultaneously. 60 amp service would only give me another 20 amps to supply the rest of the shop (lighting and outlets) and I'd rather keep those on different breakers.
don't confuse breaker size with load, the table saw may run at 15 amps or so and the dust collector at less. you won't see fla on the table saw unless your ripping 4 inch wood constantly. led lighting will be the only other load in the shop while your running the table saw. unless you have 8 arms :)

as for the 100 amp panel, both of you missed my point. get how ever many breaker spaces you need. if it happens to be a 100 amp panel, just leave the 100 amp breaker in there. the 60 amp breaker in the house panel will protect the wire to the sub-panel. the 100 amp breaker at that point becomes your main disconnect and will be there if you ever upgrade under the driveway
 

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No, I got your point, you missed mine

My suggestion was to put the 100 AMP panel in now, and use the 60 AMP breaker in the house to protect the wiring. There's no way to predict how many slots you need at this point, so the 100 AMP panel should be more than adequate for later needs. Like I said, my 100 AMP panel in the wood shop is full, no remaining slots, but I have a bunch of 240 volt machines and a 17,000 watt heater.
:vs_cool:
 

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my point was... a panel can be any size: from 2 spaces to 40 spaces. a 200 amp 8 space is a very common panel available anywhere

this is a 100 amp 6 space panel available at lowes



this is also a 100 amp 32 space panel available from home depot



neither one is very practical for his application

this is a 100 amp 20 space panel from home depot that would work fine in a shop.



i have this type 100 amp 10 space panel in my shop. with 1- 240 volt outlet for my compressor, 4 garage door openers on 1- 20 amp single breaker, 3- 20 amp outlet circuits and 2- 15 amp lighting circuits. i think i paid $35 for it with half the breakers in it. i did swap out the 100 amp main for a 30 breaker

 

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Discussion Starter · #48 · (Edited)
Well, I'm in a position of wanting to go whole-hog ($$$$), and desperately needing to get some 240v electricity to the garage to run my Unisaw (because I don't have $$$).

I'm pretty much dead in the water for any major project until I get some power to run it. I also need to make some storm windows for the house before winter gets here... But it's not a drop-dead priority.

Anyway... I got curious about the existing wiring and I opened the junction box on the left side of the garage and I found this:



The garage currently features a single switched 15-amp circuit (interior lights, motion sensor exterior light, single interior GFCI outlet, and garage door opener) plus a second three-way circuit to turn off the exterior lights from the back porch of the house.


There are 6 wires in there, they all seem to be marked "THWN" three appear to be 12 gauge, 3 appear to be 14 gauge.

Couldn't the 12 gauge theoretically carry 240v? I don't care about the three-way switch lights, so there's a line for the 15 amps I can use to supply the existing lights and opener. Eventually, I'll build some manual tri-fold doors, so the garage opener isn't going to stay indefinitely, either. I really only care about turning on lights and power tools out there.

Could I make this work with the existing wiring - a 15 amp 110v circuit and a 20 amp, 240v circuit? For the time being only, *not* as my permanent shop power solution. Not as ideal or as convenient as a proper service box, but it'd get me moving again. Crazy idea?

I also dug around a little bit on the web and found a 2005 article from Popular Woodworking (issue #150, October 2005) about wiring up split 240/110 circuits. It was written by an electrical engineer and specifically stated that it was (at the time) code-compliant to chain 110v plugs off your 240v run. it looked legit (and published in a major magazine)

Is anyone familiar with this approach?
 

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For a temporary measure you might just get a roll of 10 gauge wire and make an extension cord to run to the garage from the house.

The 12ga wire you speak of, what else is on the circuit. If you are going to take it for 240v you will have to use the white wire for a hot line. You wouldn't have a neutral for for anything 110v.
 

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One thought comes to mind - only one circuit can be run to a detached structure. In your case, to get multiple circuits, it means sub panel and 4 wire feed, with ground rod or ufer ground.
 

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i'd rather see you pull wire in there for a subpanel and make it right

in theory with 6 wires you could have one 240 volt, 20 amp circuit and two 120 volt, 15 amp circuits
3 #12 wires for hot, hot, ground and 3 #14 wires for hot, hot, neutral and tie into the #12 ground
for added safety you could put a ground rod at the garage and use gfic breakers for the 120 circuits
i wouldn't recommend it, nor would i wire it that way for you and it will probably start a firestorm on this forum >:)
it won't be code or pass any inspection
it would probably be safe
 

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i'd rather see you pull wire in there for a subpanel and make it right

in theory with 6 wires you could have one 240 volt, 20 amp circuit and two 120 volt, 15 amp circuits
3 #12 wires for hot, hot, ground and 3 #14 wires for hot, hot, neutral and tie into the #12 ground
for added safety you could put a ground rod at the garage and use gfic breakers for the 120 circuits
i wouldn't recommend it, nor would i wire it that way for you and it will probably start a firestorm on this forum >:)
it won't be code or pass any inspection
it would probably be safe

Biggest glaring problem is the use of a #14 for neutral, and tying it into the ground is a safety hazard in itself.. It's way too small, among the other myriad code violations. Why not just do it the legitimate way and be done with it.


Let's not keep posting how it "can" be done, but how it should be done.
 

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Biggest glaring problem is the use of a #14 for neutral
no problem with a #14 neutral seeing as it will be on a 15 amp circuit and only the 15 amp circuit
there is no neutral needed for the 240 volt, 20 amp circuit, it is not a 4 wire circuit
it would be a typical MWBC (multiwire branch circuit) found in many homes and is code compliant
a double breaker running two 120 volt circuits and a common neutral is very common
google MWBC



as for the combining the grounds: grounds are typically derated to a smaller wire size
it used to be that romex had 1 size down on the ground, that changed in the mid 80s
combined with the ground rod he would be safe

as stated: i wouldn't recommend it, nor would i wire it that way for you
 

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no problem with a #14 neutral seeing as it will be on a 15 amp circuit and only the 15 amp circuit
there is no neutral needed for the 240 volt, 20 amp circuit, it is not a 4 wire circuit
it would be a typical MWBC (multiwire branch circuit) found in many homes and is code compliant
a double breaker running two 120 volt circuits and a common neutral is very common
google MWBC



as for the combining the grounds: grounds are typically derated to a smaller wire size
it used to be that romex had 1 size down on the ground, that changed in the mid 80s
combined with the ground rod he would be safe

as stated: i wouldn't recommend it, nor would i wire it that way for you

Again, a single 4 wire service is the way to go. Do not assume that all 240 circuits do not require a neutral. And tying a neutral and ground together as you suggested earlier is not a safe condition. And again we are forgetting the "only one circuit between structures" rule, and that in itself is for safety. Plenty of time in the electrical world, including industrial electrical, and yes, I know what a MWBC is. Bottom line is everything proposed so far except for a correct 4 wire feed to a sub panel is not only incorrect, but in some cases actually dangerous.
 

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Discussion Starter · #55 ·
Okay, you guys make good points. As I noted earlier, I don't want to risk a fire or lack of insurance coverage for doing something really stupid. Working wood is how I relax, so I want this to be safe and to code. I'll tamp down my exuberance and not rush into a half-baked solution. Pulling new #6 wire isn't a big deal, but after measuring the distance to main breaker, I'm looking at about 75 feet total distance.



Going from 50' to 100+' of wire is a pretty noticeable cost increase - at around $65 per 100' roll of THHN wire and x4 wires, it'll run me about $250 just for copper. I realize that's not really *that* much money in the grand scheme, but I'll need to manage my costs (just bought a house and moved, so things are tighter than they used to be). Maybe I could add a junction at the house *and* inside the garage so I could get away with a 50' run with junctions inside the house and just inside the garage. I saw that done on an "Ask This Old House" video.



If only one supply is allowed by code, it seems foolish to bother one 240 feed - especially if that's all I can safety bring in.



I'll start buying the new wires for the project. I have to move some tool and materials and then rip out some drywall to get to the interior junction. I can't start on wiring immediately.



Thanks again for the detailed advice and ideas!
 

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Maybe this will work ...

I mentioned pulling separate wires earlier. It may be cheaper than a bundle of Romex because you can specify lengths to the foot and IF code permits use only 3 copper conductors with a ground stake at the shop ... I donno? Just throwing that out there based on your budget constraints...... :vs_cool:
 

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I mentioned pulling separate wires earlier. It may be cheaper than a bundle of Romex because you can specify lengths to the foot and IF code permits use only 3 copper conductors with a ground stake at the shop ... I donno? Just throwing that out there based on your budget constraints...... :vs_cool:
Code requires 4 wires, and grounding electrode. Neutral and ground separate at the sub panel, ground electrode tied to ground bar. Most new panels come without a ground bar and the neutral bar bonded to the case with a green bonding screw. This screw gets removed and the new ground bar (purchased separately) gets screwed directly to the case. Romex by the way cannot be used underground. Single conductors should be rated THWN.
 

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Maybe I could add a junction at the house
probably the only way to run it is with junction boxes at each end of the conduit. 4- #6 wires in 3/4" conduit is going to be tight anyway you run it. it would be best to run from jb to jb and then use 6/3 romex to both panels. romex will run easy in the basement. pull all but two of the #12 wires out and get a good measurement plus a couple feet from the jb to jb off the pulled wire, nothing sucks worse than coming up 2 feet short with $200 worth of wire. leave the jb off the conduit until you have the wire pulled

when your ready to pull wire, use the two remaining #12 wires to pull in the new wire. use wire lube and keep the wires straight, try not to cross them. it will make pulling a lot easier
 

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OK, then ....

Code requires 4 wires, and grounding electrode. Neutral and ground separate at the sub panel, ground electrode tied to ground bar. Most new panels come without a ground bar and the neutral bar bonded to the case with a green bonding screw. This screw gets removed and the new ground bar (purchased separately) gets screwed directly to the case. Romex by the way cannot be used underground. Single conductors should be rated THWN.
A few questions come to mind. If the main is grounded with it's own rod at the house and the neutral is not combined with the ground at the main, would it be considered a live conductor? If so, then it would also be isolated at the sub panel, correct? What's wrong with grounding the sub panel with it's own rod? Ground is ground right? Grounds and neutrals are a source of confusion here and other places. I have only one ground rod, BUT all my subs are within the structure, nothing is run underground. Thanks for your expertise. :vs_cool:
 

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I've never seen ground and neutral isolated at anyone's main box before. Seems like it would be a good practice but it's within code to mix them.

According to codes a sub-panel should have at least one ground rod of it's own.

There are times when the soil dries out enough a ground rod doesn't function. Some people have two or three ground rods connected to their main for that reason. They make a ground meter to check to see if the ground is working properly.
 
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