DC or AC wires in the same conduit with phone & cable tv

pascar
pascar Registered Users Posts: 1
in PV Installers Forum - NEC, Wiring, Installation #1
I have a project that im looking at where the PV array will be installed on a detached cottage with its own electrical service, the solar system will be interconnected to the main house with its own electrical service (ie. 2 electrical services on the property) The cottage has a (1 1/2") underground conduit from the main house to the cottage for phone/cable, Has anyone ever heard of problems running the array dc wires in the same conduit with the phone/cable tv wires?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,639 admin
    #2
    Re: DC or AC wires in the same conduit with phone & cable tv

    NEC usually does not like that... Basically, at a minimum, the "other wiring" would have to meet the same thermal/temperature specifications as the rest of the cable in the conduit (600 VAC, XXoC, etc.).

    Usually, you are better off just adding another run of conduit (or two) since you already have the trench open (and put in pull wire/rope too) so you can add stuff later.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • 2manytoyz
    2manytoyz Solar Expert Posts: 373 ✭✭✭
    #3
    Re: DC or AC wires in the same conduit with phone & cable tv

    As a general rule, I never put AC wiring near DC wiring. Very easy to induce noise onto the DC wiring. If they must cross, make them cross at 90 degrees.

    I've also found that the wiring from my PWM charge controllers also can induce noise on video lines. In this case, a security camera by my front door being monitored on a computer. Hard to see in the video, but there are horizontal lines of noise on the video display.

    Here's a sample video of the problem and solution I encountered:

    [video=youtube_share;ffXBcXPQ9gc]http://youtu.be/ffXBcXPQ9gc[/video]

    Consequently, I don't put any of my solar wiring near other wiring now. The ferrite beads did help, but didn't eliminate the noise completely.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #4
    Re: DC or AC wires in the same conduit with phone & cable tv
    pascar wrote: »
    I have a project that im looking at where the PV array will be installed on a detached cottage with its own electrical service, the solar system will be interconnected to the main house with its own electrical service (ie. 2 electrical services on the property) The cottage has a (1 1/2") underground conduit from the main house to the cottage for phone/cable, Has anyone ever heard of problems running the array dc wires in the same conduit with the phone/cable tv wires?
    Technically, I don't see an issue. The AC voltage on the TV and phone lines is very low and DC lines won't interfere with them. I don't know about code, though.

    The subject line mentions AC wiring, though. You can't combine AC and data lines in the same conduit.
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #5
    Re: DC or AC wires in the same conduit with phone & cable tv

    Agree that it is quite possible to induce HUM and unwanted signals in low level cables (phone and CATV) from even DC wiring of PV arrays. Medium and large charge controllers use switching techniques to control voltage and currents.

    On the Midnite Forum, this link was posted regarding 600 V rated Cat 5 cables made by Belden and perhaps others by now:
    http://midnitesolar.com/smf_forum/index.php?topic=122.0

    Am no code guru, the voltage rating is 600V, but I would, at the very least make entry and exit from the 1.5 inch conduit mentioned before any AC panel, so an electrician unfamiliar with this configuration would not be confused. However, in the case of these Belden cables, the max temp rating is only 75 degrees C, so could possibly not be compatible with the temp rating of the AC wiring in the conduit. Would think that an AHJ could generally have constitutional issues with this configuration.

    IF the trench was open, I would certainly just run an additional conduit for these other functions. Plastic conduit is inexpensive. But, there could still be some induced noise between each set of cables.

    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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  • peakbagger
    peakbagger Solar Expert Posts: 341 ✭✭✭
    #6
    Re: DC or AC wires in the same conduit with phone & cable tv

    I had a code guru goign over a 50 hour code update and he found a specifc reference that PV circuits could not be run in a conduit with any other voltages. His initial review indicated it was allowed but then he ran into the exception. I dont have the article number but, he is pretty good so I trusted him.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #7
    Re: DC or AC wires in the same conduit with phone & cable tv
    peakbagger wrote: »
    I had a code guru goign over a 50 hour code update and he found a specifc reference that PV circuits could not be run in a conduit with any other voltages. His initial review indicated it was allowed but then he ran into the exception. I dont have the article number but, he is pretty good so I trusted him.
    I would be interested to see that article/exception. My understanding is that you may run AC and DC in the same raceway if it is for the same system.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #8
    Re: DC or AC wires in the same conduit with phone & cable tv

    My code guy had a fit about phone, cable, cat5 in the AC conduit. Separated completely was required. It was just as well anyway cause with the 2 inch I ran was all I could do to get the conductors in for the 125 AMP sub.
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