14/3 wiring question

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  #1  
Old 06-03-06, 11:33 AM
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14/3 wiring question

Hi, i'm running 2 new circuits in the back of my house, mabye a 30 foot wiring run from the main panel. Can i use 14/3 wiring for this to run the 2 circuits? Is this what its for? I want to avoid using 2 14/2 wires to run the distance if possible. I do need to tap into one of the power wires halfway along to branch off to an outlet as well, but i plan on just putting a junction box in the basement to do this... is this ok? My code book seems to indicate its ok, and i do have a permit and am getting it inspected, i just want someone to tell me if this is bad before i begin. THanks!!!
 
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  #2  
Old 06-03-06, 02:17 PM
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Short answer: Yes, you can do this.

My advice: Don't.


This is called a multi-wire (MW) circuit. You are "sharing" the neutral wire between two hot wires. Done properly, it is perfectly safe, and has the advantage of minimizing wires and of reducing voltage drop. Done improperly, it is a fire waiting to burn your house down and kill your family.

The key to doing it properly is to ensure that the two "hot" legs are on opposite phases of your incoming power. If you can measure 220V between the two hots, you have it right. If you have 0V between them, you have the aforementioned fire hazard. It is VERY easy to get wrong, and, if you get it right, its VERY easy for you or someone else working in the panel box later to goof it up. That is why I'd advise against it...at least until you read up on MW circuits and make sure you understand EXACTLY what is going on.

One easy way to make sure you do it right is to use a double pole 15A breaker, and attach the two hots to it. Do NOT use a twin/tandem/slim breaker(s) to do it.

Do a search on this forum for multi-wire circuit and read several threads. Pay special attention to posts from RACRAFT, John Nelson, Winnie, or the other regulars here. They know their stuff.
 
  #3  
Old 06-03-06, 02:25 PM
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While this is possible, I too recommend against it. The dangers are too great if you don;t know what you are doing.

By the way, since these are new circuits, you should make them 20 amp circuits. With a 20 amp circuit you get one third more power with little additional cost and the same work.
 
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Old 06-03-06, 05:58 PM
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Originally Posted by racraft
While this is possible, I too recommend against it. The dangers are too great if you don;t know what you are doing.

By the way, since these are new circuits, you should make them 20 amp circuits. With a 20 amp circuit you get one third more power with little additional cost and the same work.
Bob, you forgot to tell him to upsize wire to #12 for the 20 amp circuit.
 
  #5  
Old 06-03-06, 09:34 PM
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um, call me stupid here, but this isn't rocket science....

If a double pole breaker is the foolproof way to do this, how is using two breakers in the same configuration 'dangerous'?

Pretty simple. Make sure the two breakers are on different phases. The configuration of the slots makes it pretty hard to put two full sized breakers on the same phase for a shared circuit and make it look like it's 'right'; either they would be opposite each other or one slot apart. Either way that's a clue you're doing something wrong.

Of course you wouldn't use two thins that were in the same slot...they're on the same phase.

I'm running quite a few shared circuits and as chirkware pointed out, either use a double pole breaker or use two full sized breakers on different phases (so one on top of the other in the slot configuration). Then as long as you know how to wire it on the other end, you're fine.

But remember that if you have a ground fault, both breakers will trip. And the only disadvantage to using a double pole breaker is that you have to turn off both circuits to work on one or the other.
 
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Old 06-03-06, 09:53 PM
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While those of us that work in the trade realize it isn't rocket science but we are trying to help DIY'rs. While you or I understand how and why the neutral can be shared, a DIY'er without that understanding can very easily unintentionally place both circuits on the same phase possibly resulting in an overloaded neutral, thus being a hazard.

When I first read this thread, I felt the same as you but after some thought I realized how easily a DIY'er could end up with a problem.

While it is easy to explain the correct way to do it, I would think those that gave negative responses to the shared neutral have seen the wrong thing happen too often to recommend it.


While I would run a shared neut without really giving it much thought, I can see many ways a DIY'er could just do it wrong. In that case, maybe it;s better safe than dead.
 
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Old 06-03-06, 10:06 PM
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In another thread that is current today, the possibility was presented that the DIYer might have to shuffle breakers around and combine normal breakers using tandems to make room for a new double pole breaker. This is where I see a proper MW circuit becoming a fire hazard. If the DIYer doesn't realize the two single pole breakers that are side by side feed a MW circuit, they might easily end up with both hots on the same service leg, either by combining them onto a tandem or by moving one to another spot. Now they have a dangerous situation and are unaware of it.

That's why I, as a DIYer, do not recommend other DIYers do MW circuits. If they do insist on it, that's why I recommend a double-pole breaker.

The only place I personally myself using a MW circuit in my home would be for a dishwasher/garbage disposal duplex receptical under the kitchen sink...and in that case, a double-pole breaker would be required since both hots are on a single yoke.
 
  #8  
Old 06-04-06, 04:19 AM
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I guess it all comes down to how comfortable you are working in and around the panel. If a someone does not have enough knowledge to know that moving breakers around indiscriminately is a hazard (that's the real hazard here, not the use of MW circuits), then they have no business doing the work in the first place. That's scary.

I myself used quite a few MW circuits; dishwasher/disposal as you did (DP breakers), some lighting circuits, other kitchen circuits, etc. This was out of necessity, as I had limited space to run wires into the attic (long story). It was done to code and inspected and passed.

As a DIY'er, I felt comfortable with the entire process, not just MW circuits. I could have created MANY hazards as bad or worse during my job, and some are a lot easier to make then the MW issue.

I agree that we all should use caution, but a good understanding of why something SHOULD and CAN be done is just as valuable as why or how it SHOULDN'T be done.
 
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Old 06-04-06, 08:21 AM
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Wow - thanks for all the responses. First off, a double pole breaker isn't practical, where i live (ontario, canada), newly added circuits to bedrooms require arc fault circuit breakers - unless i were to get a double one of these and have the bathroom (the other circuit) on the other, this wouldn't be possible.

I guess i'll do some reading - the annoying thing is i've already run the wire (not connected to the panel yet though!!!) and real estate is tight to get from the panel to the destination. But since so many people recommend against it, i probably should just bite the bullet, buy some more (a lot more!) 14/2 wire, and give'r.

This is all good knowledge - i know my electrician used some 14/3 wire at the panel location to save real estate going into it, i didn't realize that if i moved some of those breakers i might be creating a very bad situation!!!
 
  #10  
Old 06-04-06, 08:24 AM
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O, and as for the 20 amp suggestion, i'm pretty sure my code book also says 15 amp and nothing else to bedrooms - i would assume the same goes for bathrooms but i'll have to check. Only for kitchen outlets and special appliances does it mention 20 amp. I think i'll stick with 14 guage and 15 amp circuits (that and i've already bought the frickin 65$ arc fault breaker for the bedroom circuit and the 18$ GFCI plug for the bathroom!!!).
 
  #11  
Old 06-04-06, 08:33 AM
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I just checked my code book - only for 240 volt kitchen plugs is a double pole breaker or tie bar required. For other circuits is ok, but it does mention the threat of overheating if the circuits are not located next to each other. Hmmm... i wonder if theres some smart way to label the panel itself instructing any future workers that they go together.

And just so i'm clear, what would the symptoms of this problem be? If i understand correctly the curcuit would still function, but the wires would get frickin hot, is that mostly accurate? Could i use a voltmeter to test before the wires are actually connected to any receptacles? Hmm....
 
  #12  
Old 06-04-06, 08:46 AM
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a little electric basics are in order here.

when you have 1 circuit (hot) and it's neutral, there is the same amount of current returning on the neutral as there is going out on the hot. i.e. 20 amps out, 20 amps back.
When you use a multiwire circuit with 2 hots 1 neut, when the hots are on opposing phases, the neutral current from each hot will balance out with the difference between the two currents returning on the neut.i.e 20 amp on each hot would be 0 amps return current or 20 and 10 out will give you 10 amps return.

Now if you use 2 circuits on the same phase , the neutral currents will be additive which means if you have 2 x 20 going out, you will have 40 amps coming back.

This will make for a hot (literally) neutral wire.

Now with NM wire it is not that difficult to figure out. When it comes into the panel, you can visibly see that it is a 3 conductor wire adn this should clue anybody with some elec knowledge that it is a shared neut and to be sure they are on opposing phases.

If individual conductors are run into conduit, it takes more investigating to figure out the situation. It can be sone but it is time consuming. I often tape hots with their neut's together when entering the panel to indicate proper relationships. This would end up with the same situation as the NM where they are all together inone outer insulation wrap and be a visible indicator of the situation.

The idea of using a two pole breaker is so you cannot physically put the seperate circuits on the same phase. This will work in most cases but if I remember correctly there is a brand that offers a slim version 2 pole breaker that can be put on one or two phases.
 
  #13  
Old 06-04-06, 08:56 AM
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Originally Posted by 2chumpy
O, and as for the 20 amp suggestion, i'm pretty sure my code book also says 15 amp and nothing else to bedrooms - i would assume the same goes for bathrooms but i'll have to check. Only for kitchen outlets and special appliances does it mention 20 amp. I think i'll stick with 14 guage and 15 amp circuits (that and i've already bought the frickin 65$ arc fault breaker for the bedroom circuit and the 18$ GFCI plug for the bathroom!!!).
Section 210.12(B) Dwelling Unit Bedrooms: All 120 volt, single phase, 15 and 20 ampere branch circuits suppluing outlets installed in dwelling unit bedrooms shall be protected by a listed AFCI.

Section 210.8(A) Dwelling Units: All 125 volt, single phase, 15 and 20 ampere recepticles installed in the locations specified in (1) through (8) shall have GFCI protection .

(1) Bathrooms
 
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Old 06-04-06, 09:03 AM
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Originally Posted by ISC
Section 210.12(B) Dwelling Unit Bedrooms: All 120 volt, single phase, 15 and 20 ampere branch circuits suppluing outlets installed in dwelling unit bedrooms shall be protected by a listed AFCI.

Section 210.8(A) Dwelling Units: All 125 volt, single phase, 15 and 20 ampere recepticles installed in the locations specified in (1) through (8) shall have GFCI protection .

(1) Bathrooms
Did you notice the OP is in Canada? I personally do not know if our code is the same as thiers, it may be, I don't know.

He also may be restricted by a local code as well.
 
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Old 06-04-06, 09:11 AM
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Originally Posted by nap
If individual conductors are run into conduit, it takes more investigating to figure out the situation. It can be sone but it is time consuming. I often tape hots with their neut's together when entering the panel to indicate proper relationships. This would end up with the same situation as the NM where they are all together inone outer insulation wrap and be a visible indicator of the situation.
I like that for neatness, but practically, would it really matter? As long as the neutral is wired to the neutral bar, and the 3-wire hots are on different phases, does it really matter which neutral wire goes to which circuit? Even if you were to move the breakers around, you wouldn't need to move the neutral around. GFCI and AFCI neutrals of course are different, but for regular circuits, isn't the important step to make sure the hots are on different phases? Not sure how identifying the neutral makes this situation any more safe or dangerous.

Appreciate your explanation on the possible dangers of this situation
 
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Old 06-04-06, 09:16 AM
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If I have several neuts coming in or a 2 or 3 (3 phase electric) pole hot that would not have a neut, I do this so the neut is associated with the correct hots and therefor know that those hots need to be on opposing phases.

If they are not id'd any other way, it would be very simple for 2 or 3 hots from an associated group to end up on the same phase. When re-arranging hots is the panel, there is always the accidental possibility of placing the hot onto a different phase than is needed.
 
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Old 06-04-06, 09:19 AM
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Thumbs up

Originally Posted by nap
Did you notice the OP is in Canada? I personally do not know if our code is the same as thiers, it may be, I don't know.

He also may be restricted by a local code as well.
Nap,


I do now, thanks. I am aware that there are some differences between ours and theirs, and local does factor as well. Thanks for bringing it to my attention..
 
  #18  
Old 06-04-06, 09:54 AM
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If you are required to have arc fault breakers, then you have no choice. For a multi wire circuit you MUST have a 240 volt breaker.

You cannot have two separate 120 volt arc fault breakers and run a multi wire circuit.

2chumpy, you should put your location in your profile. Most of us assume the US, or at least North America if nothing is specified.
 
  #19  
Old 06-04-06, 10:36 AM
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Originally Posted by nap
If I have several neuts coming in or a 2 or 3 (3 phase electric) pole hot that would not have a neut, I do this so the neut is associated with the correct hots and therefor know that those hots need to be on opposing phases.

If they are not id'd any other way, it would be very simple for 2 or 3 hots from an associated group to end up on the same phase. When re-arranging hots is the panel, there is always the accidental possibility of placing the hot onto a different phase than is needed.
nap, could you walk me thru a scenario where this might occur? Not doubting you but I just don't understand how it matters if the neutral is labeled or not. Of course if it's 3 phase that's different, but for regular 120V shared neutral circuit, or any other regular 120V circuit, I don't see how it matters.

Thanks and I appreciate your insight.
 
  #20  
Old 06-04-06, 10:54 AM
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Originally Posted by fuente
nap, could you walk me thru a scenario where this might occur? Not doubting you but I just don't understand how it matters if the neutral is labeled or not. Of course if it's 3 phase that's different, but for regular 120V shared neutral circuit, or any other regular 120V circuit, I don't see how it matters.

Thanks and I appreciate your insight.
I can help nap.

I install a panel and share neutrals on two circuits. They are on landed on breaker number 7 and 14. Since breaker 7 is on B phase and breaker 14 is on A phase I have no proplems.

I have properly labled my panel but there is no requirement to lable the neutral of the MWBC since there is never a case where the two different circuits are on the same yoke out in the house.

Someone comes along later and moves circuit 14 to location 15 to put a two pole breaker on spaces 14/16 and thinks that this keeps the panel well orginized. and even. Now circuits 7 and 15 are on the same phase and become a fire hazzard.

I know alot of electricians who would miss this, it is something a DIY could easily make a mistake on.
 
  #21  
Old 06-04-06, 11:13 AM
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Originally Posted by jwhite
I can help nap.

I install a panel and share neutrals on two circuits. They are on landed on breaker number 7 and 14. Since breaker 7 is on B phase and breaker 14 is on A phase I have no proplems.

I have properly labled my panel but there is no requirement to lable the neutral of the MWBC since there is never a case where the two different circuits are on the same yoke out in the house.

Someone comes along later and moves circuit 14 to location 15 to put a two pole breaker on spaces 14/16 and thinks that this keeps the panel well orginized. and even. Now circuits 7 and 15 are on the same phase and become a fire hazzard.

I know alot of electricians who would miss this, it is something a DIY could easily make a mistake on.
yep, see you're point i.e. future homeowner.

Thanks.
 
  #22  
Old 06-04-06, 11:31 AM
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Like I said, when using NM or such, it is pretty simple to figure out. If you have 12/3 coming into the panel, you should understand that it is a MW circuit (usually, there a a few exceptions I can think of),and those two hots need to be on opposing phases. Most any electrician will see this and understand the correct connection. This would also apply to a conduit situation with 1 neut and 2 hots of such. It is easily figured out by those who understand but those who don't can cause themselves some trouble.

-----------------

OK, to some sort of scenario:


I understand that conduit is required in Chicago resi builds. If this is true, then consider this situation.

9 wires in a conduit. 1 green, 2 white, 6 black (the electrician ran out of other colors )

Now without association marked and not attached to breakers (the guy took them off and forgot where they were), how many 120 volt circuits do you have? how many, 240 volt circuits do you have? Which 2 hots share which neut so you know to put them on opposing phases. Remember, if you put the two hots of a three wire group on the same phase, it will still work but the neut current will be additive (see post above for some explanation). If you put the two conductors for a 240 v circuit on the same phase, you will have no effective voltage to that device and if you put one of the hots for a 240 v circuit on a single pole and put the other on half of a two pole, and end up on opposing phases, you will have your 240 but controlled by two, possibly different current rating, breakers.


I also understand that mc cable is used a lot in the east. This can be bought with many different configs so the conduit situation could very well apply to this as well.
------------------

Now the biggest problem i have is when I go into a panel (single phase in this example)and need to run another circuit but know I have a neut that can be shared still. (e.g. 3 hots and 2 neut leaving) but which 2 hots are sharing which neut and which is the separate hot/neut combo? If I guess wrong, it will still work but could be setting up a conductor over-current meltdown.
Simple solution, run my own neut but at nearly $200/ thousand feet for #12, this is not as cost effective as sharing an existing neut.

------------------

The situation is not as prevalent when using NM or some other 2 or 3 conductor cable but when you get into conduit or mc the problem shows up more.
-----------------------
So is that as clear as mud?? Now you know why I never went into teaching.
 
  #23  
Old 06-04-06, 11:40 AM
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There may be one other solution that could save you wire pulling and allow two circuits. (Keep in mind I'm a DIY'er and not an electrician, so I'd confirm this with others here who are involved in the trade.) Believe me, if anything I say below is wrong, someone will correct me (which is as it should be, just try to be kind when you do so folks).

I donít know what the Canadian code requires, but if you are allowed to use NM cable in the area you are wiring, they do make a 14/2/2 and 12/2/2 version of the cable. This is essentially two hots (black and red) and two neutrals (white and white with one or both of the neutrals marked with a black or red stripe to indicate which hot it is the neutral for. This allows you to run two individual circuits through a single cable. There will also be a ground wire in the cable.

If allowed in Canada (and by your local code), the benefit for your situation is that (a) itís less cable to pull and (b) negates the whole neutral overcurrent issue as each hot has a dedicated neutral as opposed to a common neutral in a 14/3 or 12/3 cable. This means it wouldnít matter if you hook them up to the same or opposing phases and would be able to use 120 AFCI breakers. (KEEP IN MIND THAT EVEN THOUGH YOU COULD HOOK THEM UP TO THE SAME PHASE YOU SHOULD ALWAYS TRY TO ďBALANCEĒ YOUR PHASES. This basically means if you know youíll be using the individual circuits for high-amp, heavy load devices like air conditioners, refrigerators, washing machines, etc., you should try to equally distribute them between phases; you donít want one phase of your service panel supplying all the heavy load devices and have the other phase just supplying lighting and a couple of low amp devices.) If Iím confusing you more with this, let me know and Iíll try to clarify.

Also, you said you would need to have an outlet in the middle of the run for one of the circuits. Again, depending on your code requirements, you could do this by using a junction box that will hold a receptacle. Use the receptacle as the junction for one circuit, say the black hot and itís neutral, and join the other circuit, the red hot and itís neutral, in the box with wire nuts. Just make sure you ground everything properly and donít confuse the neutrals.Also make sure the box is the correct size for the number and gauge of TOTAL wires in the box (incoming and outgoing will count as individual wires; again check your codes for this info.

I hope I havenít made you more confused with all this; I just thought it might be another solution. If you are unclear about anything I said, post your questions and youíll get the help you need.

Good luck.
 
  #24  
Old 06-04-06, 11:45 PM
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I hired an electrician to wire 2 circuits in a new addition I had just finished. After reading these posts I now realize that he has them on the same phase and it is 12/3 romex.

He charged me $30/hour and said he was fully licensed and insured, I guess I should have known better since everybody else was almost triple that price. I guess I thought Electrical work was like drywall or any other trade where anybody could do it since it wasn't rocket science.

I guess I'm worried what else he did wrong and how would I know it,this guy went out of business a few months back so there is no warranty etc. I can fall back on. I haven't had any major problems yet but I did notice that the white wire is dark brown at the connection point in the panel and it is definitely the same one he put in. I'm sure of it because his wire had the new cloth covered sheath on it compared to the rest of the older white plastic covered stuff. When he pulled the wire out of his El Camino station wagon I asked how come it was covered in cloth and he said it was the new heat resistant type

Hey Fuente, you seem real knowledgable, what would Fuente do ? WWFD
 

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  #25  
Old 06-05-06, 04:58 AM
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Fix it so they aren't on the same phase.
 
  #26  
Old 06-06-06, 07:14 AM
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Thanks so much for all the replies and practical examples!

I don't see in the code book the requirement for a 240 volt breaker, and certainly there are places in my panel where this is not done - however, because i don't understand the complexities of arc fault breakers, I will assume that the technology within an (ie the circuits used to sense arcs) requires that the neutral wire is NOT shared... unless someone can say for sure about these two things, which seems unlikely at this point, i'll go with 14/2 or 14/2/2 wire (if i can find it) all the way from the breaker panel.

Thanks again, you guys rock!!!
 
  #27  
Old 06-06-06, 07:23 AM
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Arc fault breakers also provide some GFCI protection. This is not the level required for GFCI protection for code required locations (bathroom, kitchen, outside, garage, etc.), but it is some. As such the neutral current must equal the hot side current or the breaker will trip.

Bottom line. To use 14-3 from the panel and have AFCI protection, the panel breaker must be a 240 volt AFCI breaker. The alternative is to use two runs of 14-2 or a single run of 14-2-2 and use two separate 120 volt AFCI breakers.
 
  #28  
Old 06-06-06, 07:31 AM
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O wait - just to be clear these 2 circuits are for a bedroom and a bathroom. The bedroom requires the AFCI, and it will have it. The bathroom will simply use a typical breaker but will have a GFCI plug for the outlet within (apparently my light and fan need not be branched with GFCI protection). Since they're gonna most likely use seperate 14/2 wiring, they're unrelated, and i need not use 2 AFCI breakers.... please correct me if i'm wrong.

Thanks again!
 
  #29  
Old 06-06-06, 07:55 AM
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I am not familiar with the CEC. If AFCI is not needed for the bathroom (it's not in the US) then you definitely don't want to use 14-3.

My advice is to keep the circuit comp[letely separate, useing two runs of 14-2 (or whatever is required in Canada for the circuits).
 
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