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Thread: Low and high voltage in the same conduit

  1. #16
    Licensed Electrical Contractor Speedy Petey's Avatar
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    Quote Originally Posted by ked View Post
    Communications wiring, (under 60 volts) shall also be separate. NEC 800-52
    I assume you mean 800.53 since there is no 800.52 .

    Also, this does NOT apply. 800.53 in in section "II. Wires and Cables Outside and Entering Buildings" of Art. 800.

    You are looking for 800.133(A)(1)(c), but this applies to communication conductors. I believe the OP is asking about control circuits.

  2. #17

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    The reason to keep comm circuits and control circuits and other circuits below 60 v. away from high voltage is that the high voltage wires create EMF that interferes with the comm wires. The insulation on the comm wires could be 25,000 v. insulation--same problem. Also there is the possibility of short circuit or error that will destroy sensitive equipment. Do not put a 24 v. system in a conduit with a 120v or 480 v. system.

  3. #18
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    I have a 200A whole-house transfer switch (Generac RTS) inside the garage. Installation instructions for the switch specifically prohibit running the control system interconnection leads in the same conduit as the AC power wires. Generac tech support did say, however, that for lower-power installations (my generator is only 16KW) it would be OK. It's mainly an EMF interference issue, as ked pointed out.
    Last edited by Mikey; 11-06-2007 at 05:59 AM.

  4. #19

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    Do not put a 24 v. system in a conduit with a 120v or 480 v. system.
    It's done every day with motor control wiring.

  5. #20

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    We do not put a circuit 50 volts or less in the same conduit with single phase 120 volts to ground (240 volts phase to phase).Also we do not mix 120/240 with 277/480 in the same conduit.

  6. #21

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    My advice is still: do not mix the voltage groups I mentioned above in the same conduit. I also think it is good practice to not mix 240 with 480 in the same conduit, even though it is Code legal. Our job is to create safe, efficient, Code legal installations. You can spend time trying to interpret the Code to let you do what you want, but can you convince an inspector to pass your job?

  7. #22
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by ked View Post
    My advice is still: do not mix the voltage groups I mentioned above in the same conduit. I also think it is good practice to not mix 240 with 480 in the same conduit, even though it is Code legal. Our job is to create safe, efficient, Code legal installations. You can spend time trying to interpret the Code to let you do what you want, but can you convince an inspector to pass your job?
    I am confused about this post.
    Quote Originally Posted by ked View Post
    even though it is Code legal…… but can you convince an inspector to pass your job
    If it is code legal would not the inspector have to accept?

  8. #23
    Licensed Electrical Contractor Speedy Petey's Avatar
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    Quote Originally Posted by ked View Post
    You can spend time trying to interpret the Code to let you do what you want, but can you convince an inspector to pass your job?
    Yeah. I don't get your point either.
    Inspectors do NOT write or make up the code. They ENFORCE it. That means no making things up as they go depending on their own moods and opinions.
    They may not agree with a certain code but they have NO grounds to deny a "to-code" installation.



    I spend LOTS of time interpreting the code to let me do what is CODE LEGAL and SAFE. Nothing else.

  9. #24
    criminallawyer
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    Default Low and high voltage in the same conduit

    Is there any safe and effective way to run RG-6/RG-59 cable and romex wire (power cable) through the same piece of conduit. Is there some kind of device I can purchase to restore any disturbed signal? Also, what about CAT-5 and romex wire in the same piece of conduit? Finally, if I do have to run either of these in separate pieces of conduit, would it be okay to put them in the same trench?

  10. #25
    Licensed Electrical Contractor Speedy Petey's Avatar
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    NO, you cannot run them in the same conduit. A sleeve for protection is less clear but still not advised.

    If you are talking about an underground conduit you CANNOT run romex anyway.
    Answers based on the 2008 & 2011 NEC. If you're on the '14 already I feel sorry for you.

  11. #26
    Like an engineer alternety's Avatar
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    A couple of additional points. You can get direct burial coax. It would be safer for the cable if you put it in something. If you just bury it, make sure you bed and fill around it with something that is not full of stones and sharp pieces.

    Don't use RG 59 for anything. RG 6 is much better for signal loss properties. If you are going to run phone, put it in with the coax and use cat 5. If you are going to run Ethernet, add another cat 5. You can also get direct burial phone wire.

    Keep the coax as far away from the power as is convenient. A foot or two would help. The coax does not have to be as deep as code requires for power. But you don't want to dig it up by accident either.

    As pointed out above, you must use individual power wires in conduit.

  12. #27
    DIY scratch-pad engineer leejosepho's Avatar
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    What about the wiring in a piece of machinery?

    This turning beam will ultimately have a 480v 3-phase motor fed by a cord reel passing power on down to the hook, and we will likely use a transformer to get a little 110 for the hydraulic controls that are part of the balancing system that is pressurized by a 12-volt hydraulic pump. All considered, is it acceptable to have 12-volt DC and 110-volt AC wires running together in the pendant cord, or do we need to use contactors in a box on the beam and have a single control voltage? For fabrication and testing purposes, I presently send power up through the pendant cord.
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  13. #28
    Licensed Electrical Contractor Speedy Petey's Avatar
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    Wow. A lot of different tangents in this old thread.

    It's the voltage rating of the conductors that matters, not the voltage running through them. If all the conductors in the cable are rated for at least the highest voltage present then it is fine.
    Answers based on the 2008 & 2011 NEC. If you're on the '14 already I feel sorry for you.

  14. #29
    DIY scratch-pad engineer leejosepho's Avatar
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    A few weeks ago, I was surprised to learn a 12v DC ground and a 120v AC ground together on the beam would not explode the hydraulic pump's supply battery!

    An electrical engineer is laying out a control system to propose, and the ultimate decision about that will be made in relation to overall safety. Personally, I do not like the idea of 110 volts in the control pendant, and having two voltages there together could lead to confusion and trouble during future maintenance such as when replacing a bad switch. But, maybe all we really need to add to what we already have is the contactor for the 3-phase motor.
    Last edited by leejosepho; 04-15-2009 at 06:14 PM.

  15. #30
    Licensed Electrical Contractor Speedy Petey's Avatar
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    Quote Originally Posted by leejosepho View Post
    Personally, I do not like the idea of 110 volts in the control pendant, and having two voltages there together could lead to confusion and trouble during future maintenance such as when replacing a bad switch.
    This is why only qualified experienced people should be working on stuff like this.
    Answers based on the 2008 & 2011 NEC. If you're on the '14 already I feel sorry for you.

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