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edbenedict
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# Posted: 12 Jul 2020 07:17pm - Edited by: edbenedict
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I am wiring our 450 square foot cabin for 12 volt DC to power lights, stereo, usb ports and etcetera. Our 12 volt batteries are housed in a shed about 25 feet away from the cabin.
I have already installed six 3/4 inch direct burial flexible PVC conduits underground between the cabin and the shed to run wire. Three of the conduits are METALLIC clad in PVC. The other three conduits are non metallic PVC. One of the METALLIC clad PVC conduits has already been used for my 120 volt AC needs.
The 3 non metallic PVC conduits are being used for other low voltage needs such as coax cable., speaker wire and etcetera.
In October 2019 I pulled one 4 AWG wire into each of the two remaining METALLIC clad PVC conduits, one conduit for the hot wire and the other conduit for the ground wire. Due to several 90 degree bends, I could not pull both of the 4 AWG wires into one conduit because they are too thick to pull together, even when using wire pull lubricant. But, after my wire install into separate metallic clad conduits, I learned a hard lesson about putting hot and neutral wires in separate metal flex conduits thus burning out some LED lighting I had installed in my garage. These were 120 volt AC lights, not 12 volt DC, and with 120 volt AC, the hot and neutral wires must be in the same metal conduit to prevent inductive heating and magnetism.
Now in the Summer 2020, I will be finishing my 12 volt cabin wiring. I am concerned that I have made a mistake by putting the 12 volt DC hot and ground wires into separate METALLIC clad PVC conduits. Is this even an issue with 12 volt DC wiring as it is with 120 volt AC wiring? It doesn't seem to be a problem when wiring a 12 volt DC vehicle, as many of the 12 volt DC loads are grounded to the vehicle frame or engine block, thereby returning current to the negative stud of the battery without a separate dedicated ground wire from each load.
I Google searched my concerns but could not find an answer about whether my 120 volt AC problem could be an issue in 12 volt DC wiring. I don't want to fix this "problem" unless I do in fact have a problem.
If in fact the wires in separate conduits does present a problem, can I fix it by installing the wires into two of the non metallic PVC conduits? All six of the conduits are installed in one ditch underground no more than 4 to 6 inches apart. I am thinking that whatever potential 12 volt DC magnetic flux is being generated would not be an issue if the metal cladding wasn't interfering with their transmission between the hot and ground wire. Of course, I don't want to go to the hassle of pulling out and re running the wires if I don't need to.
Any feedback would be highly appreciated.
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LittleDummerBoy
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# Posted: 12 Jul 2020 07:33pm
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You'll have no trouble.
In fact, separating them makes the circuit less vulnerable to inductive 'noise.'
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ICC
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# Posted: 12 Jul 2020 08:27pm
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I don't know all the reasons or all the potential problems that might be encountered, but the NEC states all conductors of a circuit, including grounding conductors must be run in the same raceway (or conduit). IRC states the same thing. Both NEC and IRC do not differentiate between AC and DC wiring. FWIW.
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toyota_mdt_tech
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# Posted: 12 Jul 2020 09:06pm - Edited by: toyota_mdt_tech
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OK, old electrician told me years ago, do not use a single 90', but use 2 45' bends, for this reason. Let me ask you this. I assume the bend is at the end of the runs, can you dig up just the ends, and replace the 90 with 4 45's instead and get all your 4AWG in one conduit? Or downsize to 6AWG?What size conduit did you use, 1.5"???
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Brettny
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# Posted: 13 Jul 2020 08:33am
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I would put them in the non metallic if you can. By useing two separate metallic conduits you may be making a magnet.
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Aklogcabin
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# Posted: 13 Jul 2020 10:46am
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I don’t that you will have that many amps in the wire especially with the dc power. To be concerned about the shielding on each wire to not be able to control any magnetic flux. You’re just not dealing with that much power. I believe that stereo wires have to have a metalic insulator is because they would pick up other radio waves in the air. 3/4†flexible conduit would have had to be put into the ground pretty darn flat to get a 4 ga wire in anyway I think. Pulling wires aint that easy.
Trying to think through your system. Batteries positive and negative wires hooked into your junction box. Did the wire the red to one buss bar and black to the other buss bar ? Or red to buss bad black to ground ? If red one buss and black to the other I think it should be ok. Hook it up and use a volt meter to check it out first whether it’s dc or ac. Or dc test light put clip on the brass side of the socket and the lights point on the center pin. Don’t let em touch.
Good luck man!
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edbenedict
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# Posted: 13 Jul 2020 04:21pm
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Thank you Aklogcabin....the wire pull was not that difficult with lube. I will protect the wire run with a 25 or 30 amp fuse. 25 foot red from battery positive to fuse junction. 25 foot black from buss bar back to battery negative. Are you saying that the amp flow won't be high enough to cause any magnetic or heating issues?
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edbenedict
Member
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# Posted: 13 Jul 2020 04:23pm
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Thanks for your input Bretney.
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edbenedict
Member
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# Posted: 13 Jul 2020 05:27pm
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ICC member, thank you for your response . I am a layman when it comes to electricity but I would assume that the ICC and NEC chapters you are referring to deals with AC or DC voltages high enough to harm or kill you which also requires grounding. Of course, grounding isn't needed with 12 volt DC.
In vehicles, 12 volt line power needs to be insulated wire but it doesn't need to be in a conduit. After going through the load the spent current goes back to the battery any way you want...wire, vehicle frame, exposed buss bar, engine block or any combination of these. I mention this because positive line power isn't necessarily routed adjacent to the returning negative current back to the battery. The returning current follows any path of least resistance back to the negative battery terminal. This leads me to believe that because it is low voltage or maybe because it is DC, magnetic or inductive heating issues don't apply even though the distance between the outgoing positive current and returning negative current could be 5 or 10 feet apart. When dealing with 120 volt AC, the hot line wires and neutral wires need to be as close together as possible to prevent inductive heating and magnetism. Any feedback would be appreciated as I don't want to R & R my work unless necessary.
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LittleDummerBoy
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# Posted: 13 Jul 2020 08:24pm
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I'm a 12v DC expert. You'll have no trouble.
With DC, instead of a two-way street for electrons you have two one-way streets.
With DC, 'Ground' is a design standard, not an electrical thing. I worked on Positive ground and Negative ground Jaguars. The only functional difference is which voltmeter lead you clip to the chassis. You save a lot of copper by using the chassis as the electrical return path. You could use a metal conduit as your 'chassis'. The AC won't know 12v DC is there.
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ICC
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# Posted: 13 Jul 2020 08:36pm - Edited by: ICC
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The actual NEC section (article 300) wording is "All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray..." The noted "where used" would seem to only indicate that a particular DC pair could be or could not be grounded, but the conductor wires must be contrained in the same conduit. That can be open to interpretation I suppose.
But as I stated, I don't know all the details and am not an electrician. I also know the NEC can be frustrating at times as it is not written as a DIY guide. It is just a rule book and has many references to other sections and exceptions.
I believe the NEC does mandate that grounds MUST be included when the voltage is over 50 volts. That is only addressing the ground though, not whether or not positive and negative conductors must be in the same conduit when part of the same circuit.
As for magnetics and 12 volts.... I have made some great electromagnets using even lower voltages.
Cars and trucks are cars and trucks and not houses or cabins and not covered by the NEC. What may be great for vehicles may not be great for houses and cabins. Maybe it makes a difference, maybe it does not. Apples and oranges. I don't know but question if that is a fair comparison.
Your original concern...Quoting: edbenedict I am concerned that I have made a mistake by putting the 12 volt DC hot and ground wires into separate METALLIC clad PVC conduits.
I believe the NEC does not cover the use of DC power within the structure, as for lighting, etc. If the structure is insured, and IF there was a fire that could be traced back to a DC wiring fault, the insurance company could refuse the claim. This has happened. Many off grid cabins are not insured so it doesn't matter one way or the other. However, if the structure is insured any sort of code violation can give the insurance company a legal basis for claim refusal, even if you have been faithfully paying premiums for years.
There may be no problems. You asked for feedback.
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NorthRick
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# Posted: 14 Jul 2020 04:06pm - Edited by: NorthRick
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Quoting: ICC The actual NEC section (article 300) wording is "All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray..."
My guess is that requirement is there for safety. I just makes sense keeping the conductors for a circuit together so when you are working on it you can tell what is what. It avoids sitting there scratching you're head trying to remember or figure out which conduit the other wire is in.
However, with a 12v circuit I wouldn't be overly concerned.
To create a magnet or cause inductive heating you need to create an electromagnetic field. You do that by changing the current passing through a wire. AC is changing the current 60 times a second (in the US). In a DC circuit it happens when you flip the light switch and then the current is steady until you flip the switch off. Those brief moments of changing current aren't going to cause problems.
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