Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Electrical question

ChrisJ
ChrisJ Member Posts: 12,827
I know, not necessarily the best forum to ask an electrical question but this is the forum I trust. 



I ran some 12\3 romex for an air conditioner a while back and don't need a 240V circuit.  I used the wire because hey, you never know not to mention it was free from a friend.



I want to add an outside outlet in and would like to do a multiwire branch circuit.  The outside outlet will of course be a GFCI in an outside approved enclosure.  This is in my home, not a commercial building and my panel is a Square D QO type.



My question is do I have to use a two pole (240V single handle) breaker on this, or can I use two standard 20A single pole breakers? I understand I MUST have each hot on a separate phase, I just want to make sure this is 100% to code. 



Thank you for your time.
Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment

Comments

  • MikeG
    MikeG Member Posts: 169
    A lot of controversy

    I'm not an electrician.  I've had some of these same questions, I asked our local building-electrical inspector and two electricians, and got three somewhat different answers and explanations.  My understanding is that you will need to use a 2 pole breaker, some say you can use 2 single pole with handle ties.  You have to mark that circuit so anyone at the point of origin knows it is a multiwire circuit.  If you use only single pole breakers and  shut off the AC to work on it and needed the outlet for tools etc the neutral could carry current and it would create a dangerous condition.  Both poles must be shut offf which renders the outlet useless in this case.  You also have to be carefull depneding how multiwire circuits are wired, if you remove a neutral you can potentially put 240V where you don't want it.  Code also requires a GFCI outdoors which may pose a problem on a multiwire.  Some jurisdictions are trying to get away from the multiwire circuit for safety reasons.  I have some in my shop and house with no issue, but someone not familiar with the system could run into a problem.  Eventually 12/3 or 14/3 etc will oly be used in 240V circuits or lighting circuits.  Have a pro guide you on this.  MIke
  • Paul48
    Paul48 Member Posts: 4,469
    edited May 2012
    Lost

    neutral, and why you shouldn't ground with plumbing. http://www.thecircuitdetective.com/mnpn.htm

    For the life of me, I couldn't see how dropping any neutral could be a big deal, until I saw that illustration.A very expensive , and possibly deadly problem for a plumber.
  • icesailor
    icesailor Member Posts: 7,265
    3-Wire:

    I'm not a licensed electrician. But I'm aware and I watch.

    It is my understanding, because I have seen it done often, to run three wire out of a panel making two citcuits. The red and black will be next to each other on separate circuits. You run the 3-wire to a accessible box where the black becomes one circuit and the red becomes the other circuit. The red becomes a black.  You may have 240 volts between the red and black but you could have 240 volts between any two blacks. It's the wire connection, not the color. All the white neutrals are tied together, making a common neutral.

    I've asked electricians about all this, and have been told repeatedly that it is acceptable. The upper tiered electricians will almost always run a single pair (Black, White and bare or green ground) out to a circuit. The only time I have seen the "The Wire Circuits) done is by the hot shots with the beater trucks all seemed to know something that the "other" guys with the new trucks, nice equipment, and seemed to smoothly do their jobs.
  • Ironman
    Ironman Member Posts: 6,868
    I Am A Licensed Electrician...

    And what MikeG told you is correct. I'll add one other important detail: the neutrals must be wire-nutted together and pig-tailed to any outlets, not carried through the screws and bridge of the outlet. The reason for this should be obvious: if the neutral was carried through the outlet and you had a loose connection, that would send 240 volts to everything in the circuit. There's also the personnel safety factor.



    Some locales are limiting the use of multi-wire branch circuits to appliances. I'm not sure if that's in the NEC as I seldom do house wiring any more.



    Multi-wire circuits are safe as long as a novice doesn't tamper with them, in fact, every house with a single phase service is is fed with a multi-wire from the pole!



    Again, as mentioned, make sure the hot wires are connected to opposite phases or the neutral will be overloaded. The neutral only carries the imbalance of current between the phases in the circuit when connected to opposite phases (if phase A is carrying 16amps and phase B is carrying 14amps, then the neutral is only carrying the imbalance of 2amps); but if the hots are connected to the same phase, the the neutral is carrying the sum of both phases. In this example that would be 30amps (16 + 14 = 30). This is another reason for using a 2 pole breaker: it assures the hots are on separate phases.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Zman
    Zman Member Posts: 7,330
    Thanks Bob

    Bob,

    Thanks for the explanation. I knew the how but not the why.

    Multi branch will soon be a thing of the past since it is incompatible with arc fault breakers which are required on most circuits.

    Carl
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • SWEI
    SWEI Member Posts: 7,356
    Another licensed sparkie says

    If I'm reading this correctly, you have a 120V air conditioner already powered through the 12/3 cable.  If so, then yes, you can power the other hot from the opposite phase and create a multiwire branch circuit.  You can use a two-pole breaker, though a handle tie on two single poles or a two pole non-common-trip breaker would be best.  These prevent a short on one circuit from taking both down, but comply with the NEC requirements for a single handle that disconnects both circuits.  There are a number of recent additions to MWBC requirements in both the 2008 and 2011 editions of the NEC.



    See http://ecmweb.com/nec/code-basics/branch-circuit-requirements-20110101/ for an overview.
  • icesailor
    icesailor Member Posts: 7,265
    Connections:

    I'm not the brightest bulb on the tree but I don't understand the reasoning when EACH AND EVERY NEUTRAL (WHITE) AND GROUND/EARTH WIRE IS ATTACHED TO THE NEUTRAL BAR IN THE PANEL! Or as it was explained to me that every "V" that leaves the generating facility has to go back through the earth or through the neutral system, That's why lost neutrals are so dangerous. And I've seen my share of them.

    The only place I have ever seen something approaching what you describe is in a building I work in where it is 208 3 Phase. There are  6 Taco 112 circulators, all 110 volt single phase. The electrician used a 3 phase breaker to feed three circulators and a common ground to the three single phase motors. There are disconnects on the wall. The first time I changed a motor by turning off the switch on the wall, there was current in the white, neutral wire. Because current from the other running motors were sending back current to the neutral bar while running. Now, I shut off the 3 phase breakers to stop the zap. 

    In the wires systems I mentioned in another post, ALL whites(neutrals) are wire nutted together.

    But I don't know. I'm just commenting. It seems to me that if all the white Neutrals are all connected to the neutral bar in the panel, you can't get back-feeding. Because the neutral-grounding system is so robust.

    Where I work, I see very quality wiring. I've only seen a few of the "3-wire out of the panel" and it was always done by out of State (Massachusetts) electricians. Usually they were from New York or New Jersey. The local electricians grouse about it but all say it is legal but a practice they don't do because it is a PITA and they consider it poor practice.

    In no way am I defending it. But I've also never seen the breakers tied together with a wire like I see when someone needs a 220 double pole breaker and they only have single pole ones. Then, out comes the piece of bare wire and the switches are tied together.
  • ChrisJ
    ChrisJ Member Posts: 12,827
    edited May 2012
    lost neutral

    I'm an electronic technition not an electrician so I'm not really good when ti comes to whats code and whats not code.



    My understanding is you have a neutral from the pole as well as two hots (in most houses).  The neutral is also tied to ground via a rod or water pipe in older houses and the whole reason for this is to keep neutral ( also ground)  at the same potential as earth and everything else in your house that may conduct.  If you didn't tie it to a ground rod the neutral would be floating and very very dangerous.  A lost neutral would cause the opposite problem, you are now using earth as a return and its a very poor conductor causing your neutral to again, be at a high potential relative to other things around you, for example a metal fence, a water pipe, concrete floor and so on.  Everything is relative, and when it comes to your neutral / ground you want it to be 0 relative to earth around your home.



    The devices you plug in, whether its an air conditioner, or a microwave or a light bulb don't care about the difference between neutral and earth, all they care about is the difference between hot and neutral. 



    Again, I may be wrong but this is my understanding.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • SWEI
    SWEI Member Posts: 7,356
    edited May 2012
    floating neutral

    Remember that a neutral is the midpoint between two or more hots (ungrounded current-carrying conductors in NEC-speak.)  On a single-phase service, it is connected to the center tap of the secondary of the transformer supplying the service.  This means that if the voltage on one of leg goes down then the voltage on the other leg goes up, and by the same amount (since the sum of the two must be 240V.)  When the neutral is lifted (or has resistance between it and the center tap of the supplying transformer) the midpoint between those legs "moves around" or floats based on the balance of loads between the phases.  The net effect is that a 120V circuit anywhere on that service downstream of the problem can see wildly varying voltages as other loads turn on and off.  It's not uncommon to read 170V in situations like this -- and the results are usually bad.
  • ChrisJ
    ChrisJ Member Posts: 12,827
    edited May 2012
    floating neutral

    You know that is something I never really thought about before.



    I have to assume if Leg A has some low resistance devices on it which draw a lot of currently normally and Leg B has some low draw devices on it then Leg A is going to see lower than normal voltage and B will be higher. No?
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • Paul48
    Paul48 Member Posts: 4,469
    Ice

    I took the example of how dropping the neutral on a branch circuit could apply 240 volts where you don't want it, to extreme. There's millions of homes that have their electrical service grounded through the plumbing. If a plumber was to crack a union before that ground, while holding a pipe wrench with 1 hand, and the pipe with the other, he becomes ground for all live circuits on that service.If he's lucky enough to not be holding the pipe with his free hand,every light in the house will start getting bright then dim. The bulbs may start popping, and most, if not all appliances and electronics will fry. I had a discussion with an electrician I work with and said that there was no voltage on the neutral . He set up a demonstration to show me how wrong I was with that thinking.
  • Tim P._3
    Tim P._3 Member Posts: 50
    It can be done..

    The text that supports the excellent advice you have received:



     "In multiwire branch circuits, the continuity of a grounded conductor shall not depend on device connections such as lampholders, receptacles, and so forth, where the removal of such devices would interrupt the continuity."



    "Each multiwire branch circuit shall be provided with a means that will simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates."



    Lastly, your outdoor receptacle needs to not only be GFCI, but tamper resistant (TR) and weather resistant (WR).
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,221
    My inspector is very emphatic

    that each circuit has a has it's own neutral. In a 120v circuit the neutral carries the same load as it's hot partener. 2 hot parteners could be like 2 wives. 2 much to handle, and the neutral starts to get a little hot under the collar. When you flip a light switch the little green men go scrambling off through wire through the light bulb and whatever else until they see the first neutral. They take that path because it leads home. But first they come to the panel box where all the neutrals and the equipment grounds are connected. They could run off through the equipment ground but they choose not to because it is so much easier to scoot up the main ground wire to the transformer. Occassionally the main ground wire might already be full of little green men and they have to run through the equipment ground and wade there way through the earth until they reach home base. If they are traveling through the ground they will jump up into buildings and such, anything to make there journey a little easier. STRAY VOLTAGE! It is not until they have finally reached home base and the line is full, that the light bulb will turn on. The equipment ground is primarily for protection. The one place that it actively serves as a function is in flouresent lights. The bulbs have to be within 1/2" of a grounded sheild. This creates an ionization which lets the plasma gas ignite. But it's primary function is if there is a fault somewhere in a piece of equipment to return the electrons to ground and cause the fuse to blow. The equipment ground and the neutral must be seperated from the first disconnect on. That is a whole other subject for discussion though and I need some shut eye.



    But you can do it and get away with it.....perhaps! Minimum code is not always the best giudeline to follow.
  • icesailor
    icesailor Member Posts: 7,265
    Bad Ideas:

    Hey, understand. The first time I ever saw it, I thought it was a bad idea. I was plumbing a house in Massachusetts where I work and the house was being wired by an electrician from New York. I asked around and was assured it was OK. I have only seen it done a few times and knowledgeable electricians always said it was code but something THEY wouldn't do.

    As far as "floating" or "Missing " neutrals, back in the day of Copper water services, if the ground or earth ground was clamped to a copper water pipe, and the copper was continuious from tha ground clamp to the outside, you could loose a neutral and not know it because the current had a way back. Now, ALL water services are plastic. You get a 10' driven ground or earth rod.

    I have personally seen/experienced and heard of copper water services being cut by plumbers in a trench and getting "lifted". I heard once (possibly here) that a guy was "hooked up" and couldn't let go. But he could tell his helper to go kill the main breaker in the house to stop the flow.

    Tick Tracers are a handy tool for telling if there is current there. I have two. I use them often.
  • Ironman
    Ironman Member Posts: 6,868
    edited May 2012
    Staying Up Late on the Computer

    Harvey,

    you shouldn't stay up so late on the computer; you're seeing "little green men" everywhere. :)



    As stated earlier, the only way you can overload the neutral on a multi-wire (or Edison, as they were once known) circuit is to connect the hots to the same phase. This is forbidden by code and would only be done by a novice that has no business doing any electrical work. With the hots properly connected to separate phases, the neutral only carries the imbalance of current between the phases as I illustrated above. Hence, the neutral will actually run cooler under most circumstances on a multi-wire, but it can never carrier more than what one phase is carrying.



    As far as the "little green men" finding a different path back to the transformer from the panel, that could happen regardless of whether it originated from a multi-wire circuit or not since the service connection is multi-wire between the pole and the panel.



    To me, the whole issue of using or prohibiting multi-wire branch circuits centers around the fact that we have people who call themselves electricians and Harry Home Owners who don't know what they're doing possibly doing damage or getting hurt because they're attempting to work on something they shouldn't. So we regulate it away to protect amateurs. Any seasoned electrician understands the circuit as well as every lineman.



    I have to reject Ice's statement about "the better electricians" not using multi-wire circuits. Any commercial electrician knows that if he has to pull several single phase circuits in a single conduit, he can do it with less wires, smaller conduit, less de-rating and with less cost if he uses a shared neutral. One neutral, properly sized, can carry three single phase circuits on a three phase system. What's the benefit of pulling two more neutrals in this case? None! It would actually be a liability as all three would be carrying current equal to each hot wire instead of one carrying the imbalance of all hots together. And, the PoCo engineers certainly understand the circuit since they use it on every service that has a neutral.



    If we keep going the route of making everything safe for the amateur in electrical work,

    we'll end up the same place that we've come to in hydronics: none of the new guys will be able to work on the older stuff and will insist that it be ripped out because they don't understand it.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • icesailor
    icesailor Member Posts: 7,265
    No Disagreements:

    Bob,

    Where I work, it is all residential and light commercial. An electrical plan is just a plan showing where the light fixtures are and where the switches are. So, the electrician mounts all the fixtures, ties them all together and does a "Home Run". They run backwards not forwards.
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,221
    edited May 2012
    Yes, you are right.

    It can be done. But it should only be done by someone who totaly understands what is going on. One of the hardest parts being, properly sizing the ciruit protection.

    Two-pole independent-trip breakers and single-pole breakers with handle ties that are rated 120/240 V ac have been investigated for use in line-to-line single-phase circuits or line-to-line branch circuits connected to 3-phase, 4-wire systems, provided the systems have a grounded neutral and the voltage to ground does not exceed 120 V. In other words, make sure you do not use a common trip 240/v double pole breaker. Otherwise you will cause thermal damage to equipment before the breaker trips.

    But you are correct in that we can't take all the options off the table to protect those who don't understand. With that being said I retract the "absolutely not" which was my first impulse to the question.



    The little green men are laid to rest :)
This discussion has been closed.