Running 12/2 Wire in Parallel

Discussion in 'Landscape Lighting' started by INTEGRA Bespoke Lighting, Oct 26, 2007.

  1. INTEGRA Bespoke Lighting

    INTEGRA Bespoke Lighting LawnSite Platinum Member
    Messages: 4,102

    Well I have done some research....

    A while ago the idea of running 12/2 in parallel rather then using 8/2 cable was discussed here.

    I mentioned that I had done this in the past on long runs where I had voltage drop issues. It is much cheaper then using 8/2 and more convenient then keeping 2 types of cable on hand. (note voltage drop issues NOT current/load issues)

    It was then brought up that running cables in parallel contravened the NEC, thereby NOT something that we want to be doing.

    My research into the CEC (Canadian Electrical Code) found this section: (specifically the parts in red)

    Rule 12-108 Conductors in parallel
    When conductors are chosen to be installed in parallel, the load current must be equally divided between all the parallel conductors involved to avoid overheating of the conductors. Copper or aluminum conductors may be
    installed in parallel by conductively connecting both ends to form a single conductor.

    Subrule (1) requires the following:
    • their size must be No. 1/0 AWG and larger to prevent overheating;
    • conductors must not have splices between termination points;
    • all conductors must be the same size to keep the conductor material resistance the same;
    • all conductors must have the same type of insulation to prevent damage to insulation on one conductor due to lower temperature rating or different conditions of use;
    • all conductors must be the same length to keep the conductor material resistance the same; and
    • all conductors must be terminated in the same manner at the busbars of the supply and load end equipment to ensure equal sharing of current.

    When single-conductor cables are chosen for parallel installation, Subrule (2) requires that one of the illustrated configurations in the Note to Rule 12-108 in Appendix B or a configuration recommended by the manufacturer be
    used. Additional conductors in parallel may be arranged in repetitive configurations of those illustrated. These configurations must not result in unequal division of current in all the conductors used in each phase of the cable systems (see also Rule 4-008 for sheath currents).

    Conductors in sizes smaller than No. 1/0 AWG do not have the same factor of safety nor can they handle the same installation stresses as conductors No. 1/0 AWG and larger.

    Subrule (3) allows conductors to be run in parallel in sizes smaller than No. 1/0 AWG if
    • the conductors supply control power to specific devices;
    • all the conductors are run in one cable;
    • each conductor run in parallel can carry the total load; and
    • the overcurrent device is equal to or less than the ampacity of each conductor.

    Subrule (4) also allows an exception to the minimum No. 1/0 AWG size requirement of Subrule (1) when the conductor is a reduced neutral conductor, sized by Rule 4-022, and the conductors run in parallel meet the other requirements of Subrule (1).

    Now I am not a electrical engineer, nor am I a certified electrician. But I think that as this reads, we are okay to use the 12/2 cable in parallel based on the Subrule (3).

    I would be interested in an interpretation of this by a licensed electrician and I am wondering if the NEC has a similar subrule.

    Sorry for the long post, but this stuff is important.

    Have a great day.
  2. JoeyD

    JoeyD LawnSite Silver Member
    Messages: 2,933

    • all the conductors are run in one cable;

    I think this says it all. You are not running all conductors in one cable. Not sure if I am interpeting this correctly or not.
  3. Landscape Illuminating

    Landscape Illuminating LawnSite Member
    from Maine
    Messages: 84


    Here is the NEC version of that:

    Z. Section 310-4, entitled Conductors in Parallel, is hereby amended to read as follows:

    Aluminum, copper-clad aluminum, or copper conductors of size No. 1/0 and larger, comprising each phase, neutral, or grounded circuit conductor, shall be permitted to be connected in parallel (electrically joined at both ends to form a single conductor).

    Exception No. 1: As permitted in Section 620-12(a)(1).

    Exception No. 2: Conductors in sizes smaller than No. 1/0 shall be permitted to be run in parallel to supply control power to indicating instruments, contractors, relays, solenoids, and similar control devices provided:

    (a) They are contained within the same raceway or cable,

    (b) The ampacity of each individual conductor is sufficient to carry the entire load current shared by the parallel conductors, and

    (c) The overcurrent protection is such that the ampacity of each individual conductor will not be exceeded if one or more of the parallel conductors become inadvertently disconnected.

    Exception No. 3: Conductors in sizes smaller than No. 1/0 shall be permitted to be run in parallel for frequencies of 360 Hz and higher where conditions (a), (b), and (c) of Exception No. 2 are met.

    Exception No. 4: Under engineering supervision, grounded neutral conductors in sizes No. 2 and larger shall be permitted to be run in parallel for existing installations.

    FPN: Exception No. 4 can be utilized to alleviate overheating of neutral conductors in existing installations due to high content of triplen harmonic currents.

    The paralleled conductors in each phase, neutral, or grounded circuit conductor shall:

    (1) Be the same length,

    (2) Have the same conductor material,

    (3) Be the same size in circular mil area,

    (4) Have the same insulation type, and

    (5) Be terminated in the same manner.

    Where run in separate raceways or cables, the raceways or cables shall have the same physical characteristics. Conductors of one phase, neutral, or grounded circuit conductor shall be required to have the same physical characteristics as those of another phase, neutral, or grounded circuit conductor to achieve balance.

    FPN: Differences in inductive reactance and unequal division of current can be minimized by choice of materials, methods of construction, and orientation of conductors.

    Where equipment grounding conductors are used with conductors in parallel, they shall comply with the requirements of this section except that they shall be sized in accordance with Section 250-122.

    Where conductors are used in parallel, space in enclosures shall be given consideration (see Articles 370 and 373).

    Conductors installed in parallel shall comply with the provisions of Section 310-15(b)(2)(a).

    AA. Section 310-15(b)(6), entitled 120/240-Volt, 3-Wire, Single-Phase Dwelling Services and Feeders, is hereby amended by amending the first paragraph to read as follows and adding an exception after said first paragraph as follows:

    For dwelling units, conductors, as listed in Table 310-15(b)(6), shall be permitted as 120/240-Volt, 3-wire, single-phase service-entrance conductors, service lateral conductors, and feeder conductors that serve as the main power feeder to a dwelling unit and are installed in raceway or cable with or without an equipment grounding conductor. For application of this section, the main power feeder shall be the feeder(s) between the main disconnect and the lighting and appliance branch-circuit panelboard(s), and the feeder conductors to a dwelling unit shall not be required to be larger than their service-entrance conductors. The grounded conductor shall not be permitted to be smaller than the ungrounded conductors, provided the requirements of Sections 215-2, 220-22, and 230-42 are met.

    Exception: Manufactured U.L. Listed Cables, and Listed Cable Assemblies with reduced grounded conductors shall be acceptable in residential applications only.

    This was the only version I could find online. One of the stipulations that we appear to have compared to yours is that the use of smaller wires is for controls; contactors, relays, solenoids and so on.

    Hope that helps,

  4. JoeyD

    JoeyD LawnSite Silver Member
    Messages: 2,933

    Nate told me that if you do this you are definitly violating code. He whipped out the NEC book and started rattling off everything. I bassicly said instead of wiriting this in the frum, if you want to hear his reasoning for this not being OK then you can call him directly on his cell at 760-580-4980.
  5. NightScenes

    NightScenes LawnSite Silver Member
    Male, from Kingsland, Texas
    Messages: 2,214

    I would agree with you Joey, all conductors must be in one cable and therefore, would not be allowed.

    Just MO
  6. irrig8r

    irrig8r LawnSite Platinum Member
    Messages: 4,553

    That's what I was thinking.... so if true, 12/3 would be OK then?

    Edit: Looking further at the post following Joey (#3), exceptions 2b and 2c would seem to disallow 12/3.
  7. pete scalia

    pete scalia LawnSite Senior Member
    Messages: 960

    Can someone explain the reasoning why, if the wire is in different jackets, would this be no good if polarity is maintained and the amperage rating of the single cable is not exceeded ?
  8. ChampionLS

    ChampionLS LawnSite Bronze Member
    Messages: 1,066

    Because UL has designated provisions for underground circuit cable as outlined under section 1838, revision 3. - Primarily the insulation factor as being stranded copper, sunlight resistant, wet location and direct burial.

    Anything outside of this provision is not suitable and would require conduit.
  9. pete scalia

    pete scalia LawnSite Senior Member
    Messages: 960

    I think you misunderstood my post. I was responding to running 12-2 in parallel. Both cables are direct bury low voltage cables.
  10. ChampionLS

    ChampionLS LawnSite Bronze Member
    Messages: 1,066

    I don't see a problem with that. You could even use 10/3 LUMA cable, which share a common conductor.

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