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Discussion Starter #1
Doesn't have to be anything special as long as it's "readable"... In my shop wiring post someone suggested running one line of 12x3 to power two different boxes on two different circuits.. Could someone drawing up a quick diagram as to how it would be wired from box to box and then in the breaker panel? Have done normal 12x2 wiring on one circuit, but never x3 on two.

TIA!
 

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Krylon.. said:
Doesn't have to be anything special as long as it's "readable"... In my shop wiring post someone suggested running one line of 12x3 to power two different boxes on two different circuits.. Could someone drawing up a quick diagram as to how it would be wired from box to box and then in the breaker panel? Have done normal 12x2 wiring on one circuit, but never x3 on two.

TIA!
What is being suggested is to share a neutral. Carry the 12/3 to the first receptacle, wire up the black to this receptacle, pigtail the neutral (white) and ground (bare) and continue with a 12/2 to the next device. Tie the Black on the 12/2 to the Red on the 12/3, twist up the white and bare wires respectively.

Note: Using a device for a 'feed through' is bad practice. Make joints and pigtail each device. Use large enough boxes to facilitate this (plan ahead) If you 'stab lock' your plugs in your shop, you deserve a swift kick in the nuts. Pony up and get commercial grade, or better yet, industrial grade receptacles, your stuff won't be coming unplugged as easily, and you will also be getting a better termination (less heat transfer = long happy life for plug and tools)

***REALLY IMPORTANT NOTE***

Make good and damned sure that the black and red of the 12/3 are on seperate phases in your panel (will test 240V phase to phase, if you get 0 volts, they are on the same phase), otherwise your neutral will be double loaded. Sharing a neutral on seperate phases is OK because they will cancel each other out (the load imbalance) I won't go into a lengthy explanation.
 

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Gummi's complely correct.
Commonly called "multiwire" and used in kitchens.
3 additional comments:

1. Sometimes, this type of wiring is done with the "black" to the bottom of the outlet and the "red" to the top. (split-wired) The brass bars are removed from the sides of the outlets. This is useful if you think 2 high-current devices will be plugged into the same outlet. Otherwise it's a useless PITA, and I surely wouldn't wire a shop that way. I would, wire 2 side-by-side outlets to the 2 different "sides".

2. You may be required or want to have your shop circuits on a GFI. Multiwire will require a GFI breaker, not 2 GFI outlets at the start of each run. If your shop is in th (Ae garage, you're required to have GFI protection.. I've saved my own butt many times by having all my outlets GFI'd... And I don't get nuicance trips very often.

3. You may want to use a "220" breaker -- i.e. the 2 breakers are interconnected. You would be required to do so with split-wired outlets. I do not believe it's a code requirement for typical multiwire circuits, but it makes it safer to work on later.
 

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Discussion Starter #4
Thank you guys!!

So would it be safer to run two different 12x2 lines rather than messing with the 12x3 and different wiring?
 

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Safer? No - both methods are equally as safe.

Easier? All depends on your shop layout and which outlets you want on which branch. 2 12/2's may be a teeny bit easier just because of box fills - but not enough to really matter.

12/3 is cheaper than 2x the length of 12/2.
2 GFI recepticals are cheaper than 1 220v GFI breaker.
 

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Discussion Starter #6
I was at Lowes Saturday and checked some wire prices. Indoor 12/3 x 100'( which is a hair more than I need) was $42.95. But I just checked on their website and they list Southwire-Romex 12/2(with ground) x 250' for $28.95.... So it would actually be cheaper for me to run the 12/2(wire wise).......
 

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teajay said:
Safer? No - both methods are equally as safe.

Easier? All depends on your shop layout and which outlets you want on which branch. 2 12/2's may be a teeny bit easier just because of box fills - but not enough to really matter.

12/3 is cheaper than 2x the length of 12/2.
2 GFI recepticals are cheaper than 1 220v GFI breaker.

FYI - each circuit must be able to be disconnected independently. The only time you'll use a 2 pole breaker in a proper application is for an appliance needing 2 phases of power.

Something else to consider: I don't believe in using GFI receptacles to protect a line. I prefer to have one in each location. Sure it costs you a few bucks more, but it also isolates your problem to that location rather than the entire circuit. The only time I advise people to use GFI breakers is for a hot tub. Receptacles are pretty cheap, and available in several different 'grades' Commercial grade will net you a 20A receptacle, with better springs to retain your plug, Industrial grade, typically comes with even stiffer springs, and often a more shatter resistant material on the face. Do yourself a favor, and use either Nylon or metal receptacle plates. The cheap-o plastic ones break all the time.
 

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Discussion Starter #8
Gummi - thanks for the recomendation on the GFI recepticles. Haven't decided which I was going to use yet. Probably just good 20A Industrial ones. And thanks for the tip on the face plates! :D
 

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Gummi Bear said:
FYI - each circuit must be able to be disconnected independently. The only time you'll use a 2 pole breaker in a proper application is for an appliance needing 2 phases of power.
Thought that 210.7 required simultaneous disconnection on split-wired outlets? Even just standard multiwire, I usually wire em up that way so one breaker doesn't later get moved to the other leg of the 220 - overloading the neutral. (And, I think it's permissible under 210.4)

Oh, and multiple GFI's is definitely the way to go -- I was just pointing out that the GFI recepticals are generally cheaper than the breakers.
 

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teajay said:
Thought that 210.7 required simultaneous disconnection on split-wired outlets? Even just standard multiwire, I usually wire em up that way so one breaker doesn't later get moved to the other leg of the 220 - overloading the neutral. (And, I think it's permissible under 210.4)

Oh, and multiple GFI's is definitely the way to go -- I was just pointing out that the GFI recepticals are generally cheaper than the breakers.

Good thinking,

Here's how I read it: Using the 210.7C (pg 51) that you note, I see that being applicable if you split wire a receptacle.

I see where putting them on the same breaker is not an entirely bad idea, since the neutral will still carry potential even if one leg is disconnected for service.

The term 'On the same yoke' to my understanding means 'one device'.


I see your line of thinking, and look forward to more of this. (I'm studying for my Masters license) Keep it up, I love a challenge. :D

I'll look for the code reference to put the circuits on independent switches, I can't remember where that is off the top of my head.
 

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Discussion Starter #11
Do you guys know an online source for where I could read through code for Ohio? I have been searching and coming up empty handed... I can find plumbing and mechanical, but nothing on electrical.
 

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Krylon.. said:
Do you guys know an online source for where I could read through code for Ohio? I have been searching and coming up empty handed... I can find plumbing and mechanical, but nothing on electrical.
I've never found an NEC online either (at least not without paying). It's not at all like the other NFPA code books. I have seen it on CD, but never gotten it. Unfortunately, the cheapest I've seen even a soft cover book for is $65. CHeck with your local library, or coffee it up at the Barnes & Noble while reading up on code (take a notepad, or a pocket full of dimes for copies)
My guess is that you will not be able to check it out from the library, so the dimes still hold true (it would be considered a reference book)

Another idea is to check with your governing municipality. The ones who establish the local building codes (city, county, etc.) Some communities will loan you a book to study, and allow you to take a test for a 'homeowners' permit, still subject to inspection if you are doing a significant upgrade to your residence.

Just a couple of ideas.

The NEC is updated every 3 years, and some municipalities aren't too quick at adopting the latest version. Around here, there are still a couple of towns working off of the 1996 NEC. Find out which version your municipality uses and study up on that one.

Good Luck!
 

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Discussion Starter #13
Hey Gummi - When wiring up outlets, what type of method do you use to connect two ground wires to one ground screw? I bought some Cooper Commercial grade 20a outlets and ran one ground on each side of the ground screw and tightened them down. But it doesn't seem like the best connection...
How would you do it?
 

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I'm not a big fan of looping the wires around the terminals of the devices to try and save a little bit of time. In my opinion the best way to do this is to pigtail everything. It is a much better practice to get in the habit of. Now granted most contractors will loop pretty much everything they can to try and save a little bit of time, but i can pretty much guarantee you that any good decent electrician doing his own house would pigtail everything. So what does that tell you? Take the extra time to do it right.

As for the ground wires you are mentioning just pigtail the wires. Take whatever number of SAME TYPE wires you have coming into the box, and add a short 12" or so piece of the SAME TYPE of wire, and twist them all together real good and cap it with a wire nut. Now you have all the wires spliced together and covered/insulated with the wire nut, and also one extra wire coming out to hook up to your screw terminal.

Tim
ibew local #176 electrician
 

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Discussion Starter #15
Tim - Thanks, I thought about that, but wasn't sure if it was a good method as far a code went. But that would definately be worth the extra minute or two and I'll be going back through my boxes to redo them this way!

Thanks!
 

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I use a crimp connector for grounds. (Gummi prolly knows the actual name of the connector, I can't remember it.. But it's specifically for grounds.) Pull all the grounds into one bunch, twist em up, leave 1 long pigtail for your device. Crimp away. I then push the grounds to the be the farthest back in the box. There also are green wirenuts with a hole in the top for a ground pigtail. All ground pigtails should be green or bare.

You likely don't need a full NEC book - there's huge amounts of obscure stuff you don't care about. "Code check" is a little book that has the most often failed stuff. Your library should have one. -- Oh, and you would fail an inspection around here with grounds doubled on a device screw -- go back and pigtail them.
 

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This diagram should give you a rough idea. For more plug boxes, you just carry on with 12/3, splicing all the like colors together. You have the choice of putting two plugs in each box (one plug on each circuit) or alternate, so that you use the red in one box, black in the next, and so on. More wiring diagrams on this page:

http://www.danswiringpage.com/html/diagrams.html

 
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