another electrical question

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  #1  
Old 09-14-04, 08:54 PM
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Cool another electrical question

Hello this might sound like an ignoramous of a question but I just ran 12/3 wire with ground into my garage and spent all that long time running it in the walls etc and found out that I need 3 20 amp outlets. Would it be exceptable if I were to convert all those three wires in that one line (red,black, and white) into hot wires and for the negative side just simply go off existing outlets in the garage. I suppose what I am really asking for is if the negative side wire has to be the same size gauge as the hot wire and if you don't mind can you explain the reason why this is as well. thanks alot.
 

Last edited by Michaela521; 09-14-04 at 09:42 PM.
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  #2  
Old 09-14-04, 09:56 PM
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Sorry, your plan is infeasible and unsafe. The neutral wire carries just as much current as the hot wire, overheats just as readily, and can cause just as big of a fire as the hot wire. That is why each hot wire needs its own neutral (except in one specific case).

When you said that you need three 20-amp outlets, can I assume you meant three 20-amp circuits? Because you can certainly put three 20-amp outlets on the same circuit if you want.
 
  #3  
Old 09-15-04, 08:32 AM
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The essential question is this---- what is the power-requirement in watts?

A 12/3 Branch-circuit cable has a power capacity of 220 X 20 = 4400 watts.

Good Luck & Enjoy the Experience!!!!!
 
  #4  
Old 09-15-04, 11:37 AM
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Thanks for the replys. How about this question . Does the gauge of the ground wire matter. Lets say if I had 6 12 gauge wires running in the garage (3 for hot and 3 for negative) on 3 separate 20 amp ciruits but only 1 ground wire running in the garage. Could I just simply connect all outlets etc located in the garage to that one ground wire. Again thanks alot for the replys . Mike
 
  #5  
Old 09-15-04, 12:22 PM
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I think that before we go any further we need to know exactly what you're trying to accomplish. What do you plan to use (electrical wise) in the garage? How many watts?
Is this an attached or detached garage? If detached, you can only have 1 feed to the garage. That's either a multiwire (2 hots and 1 neutral) circuit you ran, or a single circuit. You can't combine 2 separate circuits to give you more "power" (i.e. 2X20A circuits don't equal 1 40A circuit).

We need to know what you're trying to do before we can tell you how to do it safely.
 
  #6  
Old 09-15-04, 12:42 PM
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Yes, the gauge of the ground wire matters.
Yes, you can probably connect the grounding as you suggested, but I can't say for certain without knowing more about what kind of wire (more than just gauge) you are running and what kind of raceway you are using.

However, as trinitro says, this whole thread raises a lot of disturbing questions.
 
  #7  
Old 09-15-04, 01:01 PM
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The plan know is to run 12/3 wire into the attic of the garage where the other 12/3 wire with ground is already positioned and then from there I will run 3 separate 12/2 wires with ground to each of the separate 3 20 amp rated outlets. Obviously at the beginning where the main panel is I will need 3 20 amp ciruit breakers to use with those two 12/3 wires. If I had to do it all over again I would just run three 12/2 wires in the garage but I can't do that know . Thanks for the help . mike
 
  #8  
Old 09-15-04, 01:38 PM
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As I read your post, you are proposing two runs of 12/3. If you are suggesting that you can somehow use these six insulated wires (and two grounds) for three separate circuits, you are incorrect. You cannot do that.

What you can do is to use one run of 12/3 for a single 20 amp circuit, ignoring the red wire. You can then use the other run of 12/3 for a multiwire circuit. (One note, just use 12/2 for the regular circuit.) To do this, you must keep the multiwire circuit separate from the regular circuit, and follow all the rules for multiwire circuits. This must also be an attached garage.
 

Last edited by racraft; 09-15-04 at 01:52 PM.
  #9  
Old 09-15-04, 01:46 PM
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As Bob says, tell us more about how you plan to connect three 12/2 cables to two 12/3 cables. And about how you plan to connect those two 12/3 cables at the panel.
 
  #10  
Old 09-15-04, 02:15 PM
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Jeez I hate all these regulations . Ohh well I guess they keep my house from burning down . Okay here it is. If I have 2 12/3 wires running from my main panel to my attached garage that gives me 6 insulated 12 gauge wires running from my panel to the garage. That make 2 red wires, 2 black wires, and 2 white wires. I was thinking about using the 2 black wires as 2 hot wires and using the 2 white wires as 2 negative wires as people normally do. For the 2 red wires I would just simply use one for hot and color code one for negative with some white tape I have. I would obviously then use 3 20 amp circuit breakers at the box. If they all need to be on the same 120 volt circuit at the box I can probably manage that(I think that is what you meant). I hope that explains it well. Thanks for the help.
 
  #11  
Old 09-15-04, 02:43 PM
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You may wish to look into using the 12/3 wires as a “shared neutral” circuit. This would give you two 20 amp circuits, using 1 black for one circuit, the red for the other and a shared neutral (plus ground, of course). In fact, with 2 12/3 wires you can install 4 20 circuits that would be completely compliant with code.

This way you would not need to play around with using the red wires in sure a non-standard way.
 
  #12  
Old 09-15-04, 02:50 PM
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Michael, your plan violates several electrical codes. But fortunately, it is possible to wire code-compliant circuits with the same cable you already have. The solution, as impeyr says, is a multiwire circuit (aka shared neutral circuit). I strongly recommend you use a double-pole breaker for this, connecting the 12/3 black wire to one screw on the breaker, and the 12/3 red wire to the other screw. The white wire forms the common neutral. So above the garage, you can simply connect one 12/2 to the black and white, and one 12/2 to the red and white.

Then use your remaining 12/3 as it it was a 12/2 (i.e., don't even use the red wire at either end). Or if you haven't actually run that 12/3, just run 12/2 instead. Or you can get four circuits for the price of three as impeyr said.

See there. Code ain't so hard.
 
  #13  
Old 09-15-04, 02:54 PM
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As I said, you cannot do what you are suggesting.

You cannot use anything except the white wires as returns (the term nagative is meaningless in ac circuits). There are other more technical reasons why your proposal is incorrect, but I will leave them out. Suffuce it to say that your proposal is dangerous.

You must keep the circuits separate and distinct.

You may use a single 12/3 cable as a single circuit (leaving the red wire unconnected) or you may use the 12/3 cable as a multiwire circuit. Multiwire circuits have specific rules and requirements, and are NOT recommended for most do-it-yourselfers.

If you want to end up with three 20 amp circuits in the garage, then one of the 12/3 cables needs to be used a multiwire circuit, at least up the attic. At the attic you can convert the multiwire circuit to two separate circuits.

One word of caution. From your posts it sounds like you are not familiar with electrical wiring and especially with multiwire circuits. Please be very careful with what you are doing, or have a licensed electrician do the work. Multiwire circuits are dangerous.
 
  #14  
Old 09-15-04, 04:42 PM
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Originally Posted by Michaela521
Jeez I hate all these regulations. Ohh well I guess they keep my house from burning down
Actually the regulations keep people from getting KILLED!, for example your kids, wife, dog, cat, next person who owns your house, an electrician who works on YOUR wiring abortion, etc. There isn't a group of people who sit arround thinking of ways to make your life more difficult. The Code is a result of actual in field failures (often deadly) and has evolved over decades. All is focused on saving lives, maybe even your own. I would respect it and do the work correctly and not cut corners. If you don't feed comfortable with your knowledge of the NEC then I would at the least buy a couple of books on wiring or call an licensed electrician.
 
  #15  
Old 09-15-04, 05:05 PM
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First off I have to strongly agree with Racraft's last paragraph. You seem to possibly know how to make it work, but doing it correctly should be your main focus.

"For the 2 red wires I would just simply use one for hot and color code one for negative with some white tape I have."
This is very unsafe and very un-code! Circuit conductors must be in the same raceway or cable. Things like this are what get people dead!

The fix is relativelysimple, if you follow the suggestions of the previous replies.
 
  #16  
Old 09-15-04, 06:17 PM
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You disagree with Bob's suggestion that he be careful????????
 
  #17  
Old 09-15-04, 06:20 PM
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I was just kidding about that regulation thing though scott. I understand fully the importance of keeping everything to code after all I am on the doityourself forum asking questions to make sure I do it right. I believe I will go with the multiwire circuit with that 12/3 wire and then for the other 20 amp circuit I need out there I will run another 12/2 wire. I've already done some research and read things like you have to properly terminate the ungrounded (hot) conductors of a multiwire branch circuit to separate phases because if you don't the grounded (neutral) conductor can become overloaded with excessive neutral current and ultimately start a FIRE !!
Great help . Mike

P.S. As if I haven't asked alot of questions already but if you don't mind can you explain why a detached garage can only have 1 feed to it and also why circuit conductors must be in the same raceway. Thanks
 
  #18  
Old 09-15-04, 06:26 PM
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The only explanation I know of for the one feed is because the code says so.

The conductors in the same raceway has to do with magnetic fields and eddy currents and capacitive couplings and other complicated sounding things. The bottom line is that it can affect how fast the breaker trips in the event of a fault.
 
  #19  
Old 09-16-04, 04:25 AM
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No John, I said A-gree.
 
  #20  
Old 09-16-04, 07:41 AM
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Oops.......
 
  #21  
Old 09-16-04, 09:24 AM
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Sounds like you have already started to understand the workings of the share neutral circuit.

Maybe I can offer a few tips.

As you have already pointed out the most important part of the installation is to make sure you connect the two “hot” wires (Black and Red) to each electrical leg of the panel. If you use a double breaker (and you should) this is easy to do. There is a simple test to make sure you have it correct. Just check the voltage across the two hot wires. It should be 220 volts. If connected incorrectly it will be zero! (Since both wires are connected to the same leg). In this configuration there is still 110 volts on each hot wire, however, so be careful. The circuit will "appear" to work. In the correct configuration the share neutral wire, due to the magic of AC, only carries the DIFFERENCE in the total load on the circuit, which is a good thing. In the bad setup, the shared neutral carries the SUM of the load, which is a very bad thing, and as you say can lead to overloads, and serious problems.

Although not a requirement of code, I would recommend the following. Divide the shared neutral circuit into two normal circuits as soon as you are in the new location (shed, garage, etc). I normally use a separate electrical box to do this, but again it’s not a code requirement, just makes it clear what’s going on. In the box, just connect the black to the black of the new 12/2 cable, and the red to the black on the other new 12/2 cable, connect together all the neutrals and grounds, as normal. That’s it, no more shared neutral, and most of the extra concerns go away. Just run the two new circuits as you would any normal run.

One last thing, again not a code requirement, but I would keep the two new circuits derived from the shared neutral circuit in the same area or room. Again this just makes things clearer and more logical. Both circuits are controlled by the same double breaker, which means they are both disconnected if the breaker trips. If the two circuits are run to difficult and un-related locations, this can lead to some interesting diagnosis problems down the road.

Shared neutral circuits are fairly straight-forward, and with a little extra care, are completely safe.

Sorry for the long post, help this helps.
 
  #22  
Old 09-16-04, 02:08 PM
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Scott, What's a "wiring abortion"?

Doug M.
 
  #23  
Old 09-16-04, 03:48 PM
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Ah, the joys of conduit!
 
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