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    • What type of wire in conduit?

    Registered Users Posts: 107 ✭✭
    in Construction #1
    I need to run wire from my main panel in my powerhouse to a sub panel in my cabin.  It will be a 50 amp breaker, so I'm going to use 6/2.  What kind of wire should I use?  I'm getting a lot of conflicting information online, and NEC doesn't seem to be clear on this topic.  I'd like to use NM-B since it's the cheapest.  It will be in 2" PVC conduit 24" underground and will be the only wire in it.  Is that ok?  Would UF be better?  Or do I need to run individual THHN wire$?  Thanks in advance.  Great forum you guys have here.
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    • Registered Users Posts: 248 ✭✭✭
      #2
      My electrician gurus have always said individual wires inside conduit.  
      Off-Grid in Terlingua, TX
      5,000 watt array - 14 CS 370 watt modules. HZLA horizontal tracker. Schneider: XW6048NA+, Mini PDP, MPPT 80-600, SCP. 390ah LiFeP04 battery bank - 3 Discover AES 42-48-6650 48 volt 130ah LiFePO4 batteries
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    • Registered Users Posts: 6 ✭✭
      #3
      my vote  THHN.,.,just bought some today at Home D...for .56 cents per foot...8 awg
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    • Super Moderators, Administrators Posts: 33,664 admin
      #4
      The NM-B is going to be a pain to pull--If you have a longer run and/or some corners. THHN is going to be much easier to pull.

      If you don't get colored wire (black/red/white/green)--At least buy some colored electrician tape so you can wrap the last 6 inches (or whatever code is) with the correct colors.

      -Bill
      Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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    • Solar Expert Posts: 3,854 ✭✭✭✭✭✭
      #5
      NMB is not permitted to be installed in conduit 
      1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
      Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
      5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
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    • Solar Expert Posts: 795 ✭✭✭✭
      edited September 2020 #6
      Looks like 6/2UF-B direct burial is slightly more $ than the three THHN wires needed but will save the expense and installation of the PVC. 

      https://www.wireandcableyourway.com/copper-building-wire/uf-b-cable/6-2-uf-b-wire-w-ground.html
      4480W PV, MNE175DR-TR, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 360AH nominal LiFePO4, Kohler Pro 5.2E genset.
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    • Solar Expert Posts: 1,485 ✭✭✭✭
      #7
      THHN if inside conduit.  It's all about heat dissipation for given power loss per foot due to wire resistance..  NEC for 14-10 gauge is in range of 2 watts per foot of heating for gauge current limit ratings.  The more blankets of insulation the lower the current has to be to keep the temp rise down.  The more current carrying wires in a given conduit the lower the max current needs to be to keep the total heat generated per foot down within the confines of the conduit..

      Thick SOOH cord used for portable generator hookup cords is a good example of current rating reduction required for given gauge size. SOOH has a lot of multiple layers of insulation blankets that reduces heat dissipation to outside surface of cable

      Heat degrades the insulation integity over time, making it brittle and prone to cracking.  THHN has 90 degsC insulation rating.  THWN is a bit cheaper but only 75 degC insulation temp rating.  They will have corresponding max amperage rating based on maximum insulation temp rating.   Most all you can buy these days is 90 degs C rated insulation as better insulation is not as expensive as thicker copper to keep temp down.

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    • Registered Users Posts: 107 ✭✭
      #8
      Many thanks for all of the detailed responses.  It clarified a lot for me.  I'll go ahead and use individual strands of THHN.
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    • Registered Users Posts: 5 ✭
      #9
      Pretty sure to be in compliance with code, you still need to run a ground wire in the conduit beside your L1 and L2 wires.
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    • Registered Users Posts: 107 ✭✭
      #10
      Yes, but if I interpret the code correctly,  the sub panel must also have its own ground rod.
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    • Registered Users Posts: 5 ✭
      #11
      Correct.
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    • Registered Users Posts: 107 ✭✭
      #12
      Thanks for the clarification Dennis 👍
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