Replies

1. 
   1maddog | Jun 12, 2005 03:25am | #1

   As long as all wires are coming from the same panel, then only one neutral and one ground are required (you don't need to run another white and green wire). Where, I am at, there are no code requirements to specify different colored hot wires, but it does help to identify different circuits. Generally, black and red specify hot ( my house has some blue and yellow too). White is always neutral and green (or bare wire) is always the ground.
   Have you installed a new circuit before?

    

   (legal disclaimer: This information is not coming from a qualified, licensed electrician. Please consult your local authority having jurisdiction over these matters prior to completing any work, blah, blah, blah)

1. 
   WillGeorge | Jun 13, 2005 07:57pm | #8

   Just a question... I thought blue and yellow were only used for lighting and not power circuits.. Am I wrong?

2. 
   dukeone | Jun 12, 2005 04:28am | #2

   Use a different color or tape them for convenience, I don't think it is in the code. Don't share the neutral, that is code. The neutral can be overloaded if the two breakers are on the same phase and other problems, though rare, can occur. Two twenty amp circuits on the same phase could end up if they share a neutral with forty amps on the neutral. One ground however will do as long as it is rated for the largest breaker supplying the conduit.  Local inspectors have the final say on most everything though I've met some who where more knowledgeable on structure then electrical and were inspecting my work.

   KDM, electrician, retired

   Kenneth Duke Masters
   The Bill of Rights
   December 15 1791
   NRA Endowment Member
   LEAA Life Member
   CRPA Member
1. 
   nikkiwood | Jun 12, 2005 10:57am | #4

   Around here, a separate red and black wire is often used when you need to run two separate circuits through an EMT conduit.Tell me more about the potential problems with sharing a neutral.********************************************************
   "I tend to live in the past because most of my life is there."
   -- Herb Caen (1916-1997)

1. 
   dukeone | Jun 12, 2005 04:24pm | #5

   Nikkiwood: The most common problem would be if the two circuits are on the same phase or leg the current in the neutral would arithmetically add up. So if you happen to be using both circuits at high amperage the neutral wire would be overloaded. For example two twenty amp circuits with #12 wire type THHN. Pulling fifteen amps on each you would have thirty amps on the neutral. If the circuits were tapped from different phases and shared the neutral the current would be only .73 (or so, I don't exactly remember) times the phase current. Of course you might only be using one of the circuits at a time or only lightly loading them but the code takes two things into consideration; safety and longevity of installations. In the above example the neutral wire won't burn up today but would overheat causing the insulation to prematurely age and fail. Same deal with phase conductors. Another thing that can harm neutral wire are harmonics from large electronic devices (static phase converters or large computers) or big banks of fluorescent lights. One of the cures is to use a #10 or larger neutral on a twenty amp circuit (or #8 on a thirty amp etc.). By the way the size of a circuit is always the size of the breaker or fuse supplying it, not the size of the wire. In short (no pun intended) it is best to run separate neutrals all the time.

   KDMKenneth Duke Masters
   The Bill of Rights
   December 15 1791
   NRA Endowment Member
   LEAA Life Member
   CRPA Member

2. 
   maddog3 | Jun 12, 2005 04:35pm | #6

   Basically, if the shared neutral is opened at the wrong splice, 240 volts will be placed across the loads that neutral was serving. If those loads are not balanced, then damage will be done, and in a modern home full of electronic gizmos the $$$ can be very significant
   Sharing a neutral is not a big deal in homes, if done properly. It has, however become a real problem where three phase power is used.But that is another disscusion !

2. 
   user-231226 | Jun 12, 2005 10:02pm | #7

   Thanks to everyone for answering my question. Though apparently not required by code, I will, for my own reference and convenience for any future repairs, mark with colored tape the hot and neutral for the 2nd circuit. Also, besides the potential problem of overloading a shared neutral, I seem to remember that in the latest version of the code that circuits with a shared neutral require the breakers to be locked together so that when power is killed to one circuit, it killed to both. Since I do not want a situation where I have to kill power to the inside circuit just because I am doing work on the outside one, or visa versa, a separate neutral seems a good idea for yet another reason.

3. 
   WillGeorge | Jun 13, 2005 07:59pm | #9

   Just a question... I thought you could share the neutral if the gauge used would carry the combined current.  Am I wrong again?

   Gee.. I just saw...

   Basically, if the shared neutral is opened at the wrong splice, 240 volts will be placed across the loads that neutral was serving.

   Dang... I guess I have to change something in my shop.. Damn!.. Good thing I used 1 1/2 inch conduit for that run..

   Edited 6/13/2005 1:01 pm ET by Will George

1. 
   BarryO | Jun 14, 2005 12:05am | #10

   One more time:

   In the NEC, sharing a common "grounded conductor" (a.k.a., "neutral"), is called a "multiwire branch circuit":

   Branch Circuit, Multiwire. A branch circuit that conisists of two or more ungrounded conductors that have a potential difference between them, and a grounded conductor that has equal potential difference between it and each ungrounded conductor of the circuit and that is connected to the neutral or grounded conductor of the system.

   How this is breakers depends on the loads it serves, e.g. 120V-only, 240V-only, both, 120V on "split" receptacles.   Depending on this, can either use separate breakers, breakers with handle ties, or breakers with an internal common trip.

   Also, you must "pigtail" the neutral to all outlets; i.e., routing the neutral through a receptacle, so that the neutral would be broken if the receptacle is taken out of the system, is not allowed.

1. 
   WillGeorge | Jun 14, 2005 03:27am | #11

   so that the neutral would be broken if the receptacle is taken out of the system, is not allowed....

   Thank you...

   I did it that way so I think I'm OK then.. I'll double check my wiring..

3. 
   BarryO | Jun 12, 2005 10:29am | #3

   As was noted, you just need one green, sized for the largest of the two branch circuits.

   Hot colors are black, red, blue, yellow, brown, orange (I think that's the order, but don't hold me to it).

   Neutrals are white, and white with a secondary tracer color (anything but green).  I usually just hit it intermittantly with spots of blue spray paint, if there are cases where it is important to distinguish between the two.

   You can use one neutral for two circuits, if the two hots are on different legs in the breaker box.  That's called a "multiwire branch circuit" in the Code.  The regs' about how this needs to be breakered, depending on the type of load(s) being served, are a little involved.  Your safe bet is to run the two white wires, as you plan to do.

   
   

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   Edited 6/12/2005 3:30 am ET by BarryO