# 2 circuits on a 3 wire



## vdotmatrix (Mar 30, 2009)

BACKGROUND:

    * (2) new 20 amp 12/2 circuits (each with own breaker of course), coming from the panel to the switch box in the bathroom.
    * New Bathroom exhaust ceiling unit with HEAT, LIGHT, NIGHT LIGHT, and FAN. ( Panasonic FV-11VHL2 )
    * (2) 12/3 wire coming from the ceiling unit to the switch box.

    * FAN, LIGHT and NIGHT light will share neutral wire from circuit (a) pigtailed in the ceiling unit and in the switch box.
    * 4-20A single pole switches in the box will each get their respective BLACK wires from the ceiling unit.

QUESTION:

   1. (1) 3-wire cable from ceiling unit back to the box, will control the light (black wire) and night lite(red wire) on circuit (a).
   2. the 2nd 3-wire from the ceiling unit will control the FAN (black wire and nuetral from circuit A) and Heat (red wire and neutral from circuit B).

So, if you can follow this narrative, my concern is:

Can I have 2 different circuits within the same 3-wire cable (#2)?

This is OK right?


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## kok328 (Mar 30, 2009)

Can I have 2 different circuits within the same 3-wire cable (#2)?  *YES*

This is OK right? *YES*


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## triple D (Mar 31, 2009)

If you would like you could scrap one of the twelve threes, and put in a twelve two. The whole unit will run on one circuit. You could have three switch legs for light on the twelve three if you color the white wire black with a sharpie marker. Then the twelve two could be black heater and white neutral. Just a thought, unless its too late......Good luck


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## KEITH (Mar 31, 2009)

I may be missing something but the way I read it you have no neutral for the lights.

Why worry about combining circuits? just have power (A) feed switch 1 &2 for the light (black) & night-light (red) and splice the whites. do same on 2nd pair of switches with power(B) for fan and heater


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## triple D (Apr 2, 2009)

The white wire spoke of in my reply is the neutral for all four switch legs. One power to all four switches and one neutral to fan/heat/lite/night lite.


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## vdotmatrix (Apr 2, 2009)

triple D said:


> If you would like you could scrap one of the twelve threes, and put in a twelve two. The whole unit will run on one circuit. You could have three switch legs for light on the twelve three if you color the white wire black with a sharpie marker. Then the twelve two could be black heater and white neutral. Just a thought, unless its too late......Good luck



Thanks for the reply. 
This is a bathroom exhaust with heat. Current NEC codes require dedicated 20A circuit for the heat portion. I ran 2 3-wires. Diagram to follow


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## vdotmatrix (Apr 2, 2009)

KEITH said:


> I may be missing something but the way I read it you have no neutral for the lights.
> 
> Why worry about combining circuits? just have power (A) feed switch 1 &2 for the light (black) & night-light (red) and splice the whites. do same on 2nd pair of switches with power(B) for fan and heater



Can't combine circuits. That is the exercise here and my question. diagram to follow thanks


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## vdotmatrix (Apr 2, 2009)

triple D said:


> The white wire spoke of in my reply is the neutral for all four switch legs. One power to all four switches and one neutral to fan/heat/lite/night lite.



The NEC requires an isolated dedicated 20A for the heat, I wanted to completely isolate the heat circuit all the way back to the panel ...I am not sure if this also means the neutral wire.


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## vdotmatrix (Apr 2, 2009)

KEITH said:


> I may be missing something but the way I read it you have no neutral for the lights.
> 
> Why worry about combining circuits? just have power (A) feed switch 1 &2 for the light (black) & night-light (red) and splice the whites. do same on 2nd pair of switches with power(B) for fan and heater


View attachment 3_wirePS.bmp


*Can't combine circuits.* That is the exercise here and my question; neutral wires are pigtailed in the switch box and in the ceiling for the fan,light and night light and are not shown for either circuit in this diagram as well as the ground wire(s).

The HEAT's 12/3 shares nothing with the other circuit except the yellow covering on the cable; the heat 's red and the neutral belong to that 'heat" circuit.

So....I am sorry I didn't return to this forum earlier. I went to city hall and nailed down one of the electrical code enforcement folk and they said I was spot on with my wiring reasoning...I am no pro...

So if were to have pigtailed ALL the neutrals, for all four devices in the switchbox and in the ceiling, would this have been KOSHER?

I know the word neutral means neutral but wouldn't that be mixing stuff across circuits?  
ALL devices will have their separate switches.

thanks


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## kok328 (Apr 2, 2009)

Ok, here's a technique that is not commonly utilized in residential applications but, is still kosher.
You can share a neutral conductor between two individual circuits as long as they are from opposite phases in the load center (i.e.-slots 1&3 are on the same phase whereas, slots 1&2 are on opposite phases).  Therefore, being that these are dedicated circuits, it would be safe to use just one neutral out of your 2 12/3 runs, for the entire bathroom.
So depending where you put those (2) 20A breakers in the load center, will depend on whether or not all those neutrals bundled together will be OK or not.


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## vdotmatrix (Apr 2, 2009)

kok328 said:


> Ok, here's a technique that is not commonly utilized in residential applications but, is still kosher.
> You can share a neutral conductor between two individual circuits as long as they are from opposite phases in the load center (i.e.-slots 1&3 are on the same phase whereas, slots 1&2 are on opposite phases).  Therefore, being that these are dedicated circuits, it would be safe to use just one neutral out of your 2 12/3 runs, for the entire bathroom.
> So depending where you put those (2) 20A breakers in the load center, will depend on whether or not all those neutrals bundled together will be OK or not.



WOW! That is where being an electrician can save one a lot of time and cost down the road. Yeah, I put them both on the other side, bottom right in the panel... The heat circuit are the red and white to the right side..not neutrally pigtailed as you can see the others are! 
 I ran the 2 12/3 to keep the number of wires in to either boxes down to a minimum since after all, the switch box is only 34cu blue box and i may be approaching the limit of number of wires going into it...

OMG, I hope I haven't exceed the limit of wires going into this switch box


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## kok328 (Apr 3, 2009)

not even sure what I'm looking at in the second pic but, don't like what I'm looking at if I'm seeing it correctly.  And the first pic isn't close enough to read anything, it's just an exposed load center.
For all practical purposes, you could have pulled one 12/3 wire from load center to switch box.  Share the neutral (white), heater on the black from phase A (breaker #1) and light and fan on the red from phase B (breaker#2).


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## vdotmatrix (Apr 3, 2009)

kok328 said:


> not even sure what I'm looking at in the second pic but, don't like what I'm looking at if I'm seeing it correctly.  And the first pic isn't close enough to read anything, it's just an exposed load center.
> For all practical purposes, you could have pulled one 12/3 wire from load center to switch box.  Share the neutral (white), heater on the black from phase A (breaker #1) and light and fan on the red from phase B (breaker#2).



Don't know what you mean about what you don't like in the picture, but the diagram clearly shows what I have done in the previous post.  ...the other stuff about different phases and such may be beyond the scope of the average home owner doin his own work....I have kept things simple as far as I can.....Thanks for your response!


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## kok328 (Apr 3, 2009)

No worry, it's just a personal preference thing w/me.  I don't like to see wirenuts in a load center and I've never seen any diagram in any of your posts.  I'm always hesitant to redirect someone unless they are doing something wrong.  There are multiple ways to accomplish what you are doing and being that you understood your approach, I just went with it but, then later advised you of alternative approaches (of course my method would leave the average homeowner scratching their head).  You'll be just fine with either setup.


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## vdotmatrix (Apr 3, 2009)

KOK Man thanks for looking. I appreciate a place like this where people can come in and get help doing some of this stuff...Now I have learned a different aspect of wiring which I will read up about which is phasing in regard to wiring!!!! We save a lot of money doing a lot of this work ourselves..

I do like to caution people who do it yourselves with regard to plumbing and electrical work; HAVE THE WORK INSPECTED BY YOUR LOCAL CODE ENFORCEMENT PEOPLE and pull a permit.40 or 50 dollars is a small price to pay for expert advise on the work you do on your own home. After all, you don't want to endanger your family with work done that is not up to the latest code. The other reason to have stuff inspected , especially electrical , is that if you do have a fire, the Marshall will check at city hall to see if your work was approved, if not your insurance might not pay for damages......

Cheers and thanks to everyone!


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## vdotmatrix (Apr 4, 2009)

kok328 said:


> No worry, it's just a personal preference thing w/me.  I don't like to see wirenuts in a load center and I've never seen any diagram in any of your posts.  I'm always hesitant to redirect someone unless they are doing something wrong.  There are multiple ways to accomplish what you are doing and being that you understood your approach, I just went with it but, then later advised you of alternative approaches (of course my method would leave the average homeowner scratching their head).  You'll be just fine with either setup.



MAn I was making Waffles for breakfast this morning and i was thinking about "wirenuts in the load center" and was trying to figure what your were talking about. LOAD Center, load center....OH, he means the electrical panel!!!!!!!!!!!!!!

Of course!!!!!!

Okay...I don't like it either but you have to have some background. The contractor that put in our new addition 5-6 years ago ended up with a few circuits that went NOWHERE at all. But they were attached to a breaker....

I needed a slot on that side of the , a-hemmm, LOAD CENTER, for a welding circuit for the garage and saw that one....I pulled out the wire and secured everything out of the way and capped everything with wire nuts until I can go in and trace this perfectly good 12/2 20A circuit to nowhere through the basement ceiling and so on....

That is why yuo see the blue wire nut!!! GOOD EYE DUDE!!!!!!!!!!!!


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## kok328 (Apr 4, 2009)

Correction to my previous post where I stated:
_"You can share a neutral conductor between two individual circuits as long as they are from opposite phases in the load center (i.e.-slots 1&3 are on the same phase whereas, slots 1&2 are on opposite phases). "_

Slots 1&2 are on the same phase & slots 1&3 are on opposite phase.


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## vdotmatrix (Apr 4, 2009)

kok328 said:


> Correction to my previous post where I stated:
> _"You can share a neutral conductor between two individual circuits as long as they are from opposite phases in the load center (i.e.-slots 1&3 are on the same phase whereas, slots 1&2 are on opposite phases). "_
> 
> Slots 1&2 are on the same phase & slots 1&3 are on opposite phase.



Well there ya go! I would have failed the inspection ( not because of you), if I would have located the breakers on the wrong side of the LOAD CENTER. 

This is a way advanced electrical concept/technique, which would have made the Inspector otherwise, not have to examine the load center for this premise; but this could have saved wire if you didn't have enough room in the box due to wire volume calculation limit and would have been clever!

Wow what a mess, to have to have gone back in and rewire the load center for opposite phases for these 2 circuits....uggg.

Alright Poindexter, now I have to know...from the picture of my 40 slot load center, the 2 "new" breakers for this project are located on the right hand, "even" side, #36 and #38.

Are these circuits phased equally or opposed?


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## kok328 (Apr 4, 2009)

36 & 38 are on opposite/adjacent phases.

However, if they were not, you don't have to rewire anything, just move the circuit breakers.


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## vdotmatrix (Apr 13, 2009)

My project passed both electrical and mechanical final inspections this morning!!!

Thanks to everyone for their interest!!!


cheers


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## triple D (Apr 13, 2009)

I have never heard of running a dedicated circuit to heat section of fan. Can you direct me to that code? So I can educate myself And by the way, with two seperate circuits landing in the same switch, I think you need to put both those circuits on the same breaker. This requires a two pull breaker, (240v) wich means you can tie your two breakers together, or trade out for a two pull. I cant believe the inspector missed that one. Oh well, I guessed he passed ya off. Good work on your project.


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## vdotmatrix (Apr 13, 2009)

LOL

*"I have never heard of running a dedicated circuit to heat section of fan. Can you direct me to that code? So I can educate myself."*

Sorry that you haven't! 

2008 NEC: Bathrooms are required to have 20A circuits. 

The specific code is probably not as important, but more the principal involved, so pull up a seat  

This particular heat element for the PANASONIC FV-11VHL2 draws 1425Watts. A 15A circuit has a total capacity of 1800watts but the safe capacity is 1440watts. A 20A circuit has a total capacity of 2400watts with a safe capacity of 1920watts. The manufacturer recommends 20A circuits.

So, now a days, it makes more electrical sense to put high wattage devices on their own dedicated circuits: microwaves, dishwashers, particle accelerators, stoves, radiant floor heat, bathroom heat because in many cases, the appliance approaches the safe capacity of the device. 

Besides, this product has HEAT, LIGHT, NIGHT LIGHT AND the FAN in the same unit and it just draws too much juice for one circuit-one 20A circuit; but more importantly, and i knew this, the inspectors at City Hall made this a requirement on my plans, before they approved them and I began the work.

Also, the branch circuit that supplies the fan and light, also supplies the GFCI outlet over the sink and the vanity light. If EVERYTHING were on a 20A circuit, including the HEAT and someone plugs in a hair dryer-THE LIGHTS AND EVERYTHING are going OUT !!! lol  

*"And by the way, with two seperate circuits landing in the same switch, I think you need to put both those circuits on the same breaker. This requires a two pull breaker, (240v) wich means you can tie your two breakers together, or trade out for a two pull."*

Absolutely NOT! For one thing, in my simple residential bathroom project, the separate circuits are exactly that-SEPARATE; Separate romex, Separate Breakers and Separate Switches! 20A separate switches-as a matter of fact! 

I used the Pass & Seymour PS81120I 20A combination switch which has this nifty (re-usable) tab to split the circuit; I  used the BIG switch for the heat and the 2 top switches for the light and night lite. I have them installed with the big switch on the bottom  It is detailed in my wiring diagram in a previous post

The fan (29watts) is controlled by a Lutron MA-t51-IV timer. The 2 decora styled controllers fit nicely in a 2 gang box. The 3 switch in the one gang was a life saver otherwise I'd have to put in a 3-gang monstrosity to house a fan timer, light and night light and a separate switch for a separate circuit; most triple switches that i found at Home depot or Lowes were all on the same circuit.

Dude, The Code Enforcement Division of any municipality would never just "PASS ya OFF" on an electrical matter where the main purpose of an electrical inspection is to save lives through fire protection. These guys know their ****, unlike me 

If you are interested in Online Access to NFPA 70®: National Electrical Code® (NEC®) Softbound, 2008 Edition you can visit the NFPA website, create a free account and pour through the 2008 NEC for the specific code.

Another excellent reference is wiring simplified, 42nd edition.

and lastly, this is so very helpful for me...Black and Decker: Complete Guide to home wiring

Thanks for being interested ! This is a great forum!

Cheers


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## kok328 (Apr 14, 2009)

Good Job!  I just wish the licensed electricians that wired up the bathrooms in my home were able to realize what you have.


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## vdotmatrix (Apr 14, 2009)

kok328 said:


> Good Job!  I just wish the licensed electricians that wired up the bathrooms in my home were able to realize what you have.



Aw Shucks! I installed another panasonic product downstairs bathroom but without the ceiling heat cuz i had installed floor heat (nice). The biggest reason for going panasonic was that it is sooooooooooo quiet!   

I used the heat part this morning for the first time during a shower and it was awesome!!!

cheers!

BTW, with this and other forums:  YOU CAN DO IT ALL YOURSELF!!!!!!!!!!!!


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## triple D (Apr 14, 2009)

Look, in my reply, I said (I think). Now what had me concerned was this talk of phasing wires and sharing neutrals. It is not a code issue to have two seperate circuits from seperate wires in the same box on seperate breakers like I (thought) it was. However at no point along those circuits can the neutrals touch. I and others like me volunteer ourselves to assist people in a safe way. I am simply trying to do that for you. Are your neutrals touching? And no code exists, or ever has, that requires a dedicated circuit for your fan/heater. My idea for you was one any electrician would have had. One 12-2 for the entire fan/heat/lite. And of course a dedicated 12-2 for the gfi plug, and vanity light. This was just a suggestion that may have made things a little easier for you. I did not intend to offend you, I was genuinely interested in a code reference because I would have learned a new one. Today I checked and there is not one for that. And you would be amazed at what some other people have done that these inspectors that I have been dealing with for over ten years have passed off before. I sorry to be offensive, Dan


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## kok328 (Apr 14, 2009)

Wish I had a 20A/12AWG circuit in my bathroom to accomodate all that plus a hairdryer and a heated towel bar.  15A/14AWG just won't cut it.


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## DaveyDIY (Apr 14, 2009)

A 15a 1800w circuit has a safe rating of 1800 watts
A 20a 2400w circuit has a safe rating of 2400 watts
 = in both cases provided it is not something that is a continous load
Actually there is a lot of leeway in what the wiring can handle
The breaker will almost always kick off before the wiring has a problem so long as the correct gauge/breakers are used
There isn't an 80% rule for loading, unless it is something with a motor - AC etc or something that will be a continous load - more then "x" hours
I load all of my light circuits to the full rating of the breaker

Under NEC 2008 a multi-wire circuit is required to have a double breaker so that both hots shut off. This is the preferred method as it automatically puts the 2 hots on opposite sides - "out of phase"

12-3 = 2 hots & a neutral & a ground
If fed out of phase the load blances against each other on the neutral
IE 15a on one, 10a on the other - neutral carries 5a

If on the same phase the loads ADD for the neutral
IE 15a + 15A = 30a on the neutral - TOO MUCH!!

The other option is to have 2 single breakers & they must have a tie bar - so both shut off

The dedicated 20a bathroom circuit can be shared among bathrooms
So long as it feeds only outlets in the bathrooms & only the bathrooms
I don't recommend it
Running a dedicated circuit to high use appliances is an excellent choice
In many cases the Mfg requires it
There is wording the NEC requiring fixtures to be installed per Mfg instructions
Unfortunately some Mfg's have no clue, some lean very much towards extreme safety - afraid of legal problems - lawsuits


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## vdotmatrix (Apr 14, 2009)

triple D said:


> Look, in my reply, I said (I think). Now what had me concerned was this talk of phasing wires and sharing neutrals. It is not a code issue to have two seperate circuits from seperate wires in the same box on seperate breakers like I (thought) it was. However at no point along those circuits can the neutrals touch. I and others like me volunteer ourselves to assist people in a safe way. I am simply trying to do that for you. Are your neutrals touching? And no code exists, or ever has, that requires a dedicated circuit for your fan/heater. My idea for you was one any electrician would have had. One 12-2 for the entire fan/heat/lite. And of course a dedicated 12-2 for the gfi plug, and vanity light. This was just a suggestion that may have made things a little easier for you. I did not intend to offend you, I was genuinely interested in a code reference because I would have learned a new one. Today I checked and there is not one for that. And you would be amazed at what some other people have done that these inspectors that I have been dealing with for over ten years have passed off before. I sorry to be offensive, Dan



My goodness. Please don't feel like you were being offensive, My tone is a little stilted in my writting style. Excuse me 

The different circuits do not share neutrals.

The only code i could possibly think of would be not to over load a circuit to capacity which is something like not exceed the wattage capacity for a given rated circuit....now I am interested on what NEC codes apply to my project. 

Now I have another project 

cheers!


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## vdotmatrix (Apr 15, 2009)

DaveyDIY said:


> The dedicated 20a bathroom circuit can be shared among bathrooms
> So long as it feeds only outlets in the bathrooms & only the bathrooms
> I don't recommend it



Lemme See, I came across this situation when planning this 20A circuit and whether or not this circuit could supply the outlet, the small vanity lights on one branch, and the Light(s) and fan in the ceiling.

Again, I had to plan the projected wattages for this circuit. 

A dedicated 20A circuit is required for all bathroom receptacles, unless the circuit ( which still must serve only bathroom loads) supplies only one bathroom. In this case,  the 20A circuit may serve the lighting outlets as well as the receptacle within the one bathrrom Thus, you may supply any or all bathroom receptacles ( in however many bathrooms) on a 20 a circuit, or all the load, but in only a single bathroom, on a similar circuit.


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## kok328 (Apr 15, 2009)

Ok, I'm lost now (not really) but, you see my point.

*DaveDIY says:*
_"12-3 = 2 hots & a neutral & a ground
If fed out of phase the load blances against each other on the neutral
IE 15a on one, 10a on the other - neutral carries 5a
If on the same phase the loads ADD for the neutral
IE 15a + 15A = 30a on the neutral - TOO MUCH!!"_

*TripleD says:*
_"However at no point along those circuits can the neutrals touch. I and others like me volunteer ourselves to assist people in a safe way. I am simply trying to do that for you. Are your neutrals touching?"_


Also, I'm curious, DaveDIY, why would you want to nusiance trip a non-offending circuit w/a two pole breaker?

Why would you run a 240V circuit when the destination is not 240V?
_"Under NEC 2008 a multi-wire circuit is required to have a double breaker so that both hots shut off. This is the preferred method as it automatically puts the 2 hots on opposite sides - "out of phase""_

I'm not totally sure what you mean by a "multi-wire circuit" but, I don't believe what vdotmatrix is doing, constitutes a multi-wire circuit or were you referring to my input on sharing a neutral.  This still does not constitute a "multi-wire circuit".

Again, I'm curious and would like to be enlightened because if what your saying is true, I've got a ton of wiring problems in at least 4 out of 5 plants I work in.


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## DaveyDIY (Apr 15, 2009)

kok328 said:


> Ok, I'm lost now (not really) but, you see my point.
> 
> *DaveDIY says:*
> _"12-3 = 2 hots & a neutral & a ground
> ...



It s a new change in NEC 2008
When you are running a multiwire circuit you are sharing the neutral between the 2 circuits. You do not have to go back & fix pre-existing wiring. In 2005 only the connected bar was required between the breakers. 
But 2 problems were identified:
#1 People were not installing the bar, or it was removed
As a result the breakers couild end up on the same phase & the power doubles on the shared neutral from the 2 circuits
#2 One breaker could be shut off, the other left live
Since this is a shared neutral power could flow on the circvuits that is shut off via the shared neutral

A 240v breaker is now required to prevent this
You are not supplying 240v, you are supplying 120v to 2 different circuits & using a shared neutral

As long as you have 2 circuits & seperate neutrals you are fine
This is only for Multi-wire circuits that share a neutral
Neutrals from 2 different circuits in the same box should not touch
All of the grounds are supposed to be tied together in the box

Hope that clears it up?

I have 3 setups using multiwire circuits
Each one is fed w/a 20a 240v breaker, power goes to a 40a dual 120v timer
After the timer there is a seperate run of 12-2 (GFCI protected) to outlets in my front garden & around the house
My multiwire circuit is only 12" long as the timers are connected to my panel  
I knew of the upcoming change for 2008 so I used the 240v breakers
It makes sense, if the breaker is shut off then I know all power in the timer is off

The code is always changing - updated every 3 years
The wording can be very hard to understand
I've been in discussions with electricians, Inspectors & others on certain aspects of the code. In some cases each one has a different view of what the code actually is saying

By code you can run a 20a 120v circuit - UF wire - 12" deep without conduit. So long as it is GFCI protected befor eit goes in the trench. I wanted to run 2 circuits in the trench (6" wide), both 20a GFCI protected. Everyone I ran it by said that was perfectly acceptable
My Inspector did not fully agree, he said I needed 12" between the circuits in the trench. So I ended up running conduit


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## speedy petey (Apr 15, 2009)

kok328 said:


> I'm not totally sure what you mean by a "multi-wire circuit" but, I don't believe what vdotmatrix is doing, constitutes a multi-wire circuit or were you referring to my input on sharing a neutral.  This still does not constitute a "multi-wire circuit".


A "multi-wire branch circuit" is the correct term for a shared neutral circuit.
This is two (or three in the case of a 3-phase MWBC) hots sharing one neutral where the line conductors are placed on different "legs" of the panel as Dave described.


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## kok328 (Apr 15, 2009)

Thanks Dave, now I understand.
So I guess the gist of it is, do not create a multi-wire circuit where you can not tolerate one circuit tripping the other.

Thanks Again.


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