Bundling DC cabling together through plastic electrical conduit

Hairfarm
Hairfarm Solar Expert Posts: 225 ✭✭✭
in Off Grid Solar & Battery Systems #1
Is it ok for wire carrying dc current to be bundled together though plastic conduit? The wire sizes are two 4/0, six 10AWG, and two 2AWG wires. 10 wires in all. Obviously all of the wire is insulated, not bare. Those wires all have to be fed through a common point through 2 inch plastic conduit into my utility closet.

I know that AC and DC wire must cross at a 90 degree angle, but is it ok for DC wiring to touch each other as it runs through the conduit as evidenced in the attached image. The wires will be carrying different current/s.

Attachment not found.

thanks,
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  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    #2
    Re: Bundling DC cabling together through plastic electrical conduit

    Its ok for dc cables to touch, however the issue is fill factor. Under the NEC how many cables you have in a single conduit dictates the ampacity of the conductors. Which is about heat disapation really. What i do know is that if the conduit is really short, like inches, fill factor doestn apply as it vents. Someone more familiar with US code will be able to say more clearly.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
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  • SkiDoo55
    SkiDoo55 Solar Expert Posts: 414 ✭✭✭
    #3
    Re: Bundling DC cabling together through plastic electrical conduit

    If that picture is actual example of what you were going to use, it won't meet US NEC code. Need to go to the fill charts or you can find on line. http://www.electrician2.com/calculators/rf_calculator.html.
    GT3.8 w/4600W Trina 230W, TX5000 w/5000W ET-250W, XW4024 w/1500W ET-250W, 4 L16, 5500W Gen. (never had to use) Yet!!
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #4
    Re: Bundling DC cabling together through plastic electrical conduit

    Hi Hair,

    Looks like this is a 12 V system, so probably it will not be inspected ...

    But, as a technicality, the 4/0 cable has to be Fine-Stranded, and will be somewhat larger in diameter than the usual cables speced in the tables and calculators. Do your best to select the exact cable that you are running in the conduit, for the best result.

    Also, with ten current carrying conductors in that conduit, the Ampacity ratings should be checked, as again technically, the ratings for ampacity should be reduced to 50% of what is shown due to the combined heating effects of all of the conductors together in the conduit.

    Some of your cable sizes probably have been selected, based on voltage drop, not just due the current flowing, and probably the #10 cables are from PV, which may not be near the max Ampacity rating ... but an inspector might not go along, if this was to be inspected.

    Several conduits will help reduce the fill, and the number of conductors as well.

    Have fun with the installation, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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  • Hairfarm
    Hairfarm Solar Expert Posts: 225 ✭✭✭
    #5
    Re: Bundling DC cabling together through plastic electrical conduit

    The raceway calculator results state that my minimum raceway opening should be 2 inches (?) If I'm interpreting the results correctly, then it seems like my 2 inch conduit should be ok for my 10 cables.
    Looks like this is a 12 V system, so probably it will not be inspected ...

    But, as a technicality, the 4/0 cable has to be Fine-Stranded, and will be somewhat larger in diameter than the usual cables speced in the tables and calculators. Do your best to select the exact cable that you are running in the conduit, for the best result.

    You are correct Vic. It's an off-grid 12V install that will likely never be inspected.

    I was mainly more concerned with a problem with some sort of voltage interference problem with all of the DC cable touching each other as they go through the 2 inch race and not so much with an inspector. Hope that makes sense.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,617 admin
    #6
    Re: Bundling DC cabling together through plastic electrical conduit

    AC Cable pairs expecially, and it is good for DC cable pairs too--Pairs should be together in the same raceway/conduit/bundled together.

    For AC cables, they create magnetic fields that can create interference or even cause heating in sheet metal boxes if the Hot and Return cables go through different holes (causes circulating currents in the metal box).

    With DC (and AC) cables in pairs, it reduces any radio frequency radiation and it reduces the chances of picking up interference (like a near by lightning strike) because the paired cables make a poor antenna.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    #7
    Re: Bundling DC cabling together through plastic electrical conduit

    BTW if the 4/0 are battery cables, and unfused as far as the disconnect, then I always put them in their own conduit, actually i put each cable in its own conduit. Call it paranoia, but you can never be too careful with batterys.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


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