Running Romex 14/3 with red wire as 12+ - Fiberglass RV


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Old 11-30-2015, 09:11 PM   #1
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Running Romex 14/3 with red wire as 12+

So I had this crazy idea, just wanted to put it out there and see what people thought and how reasonable/safe this sounds...

From what I could glean both the 110v and 12v system are grounded to the frame in a standard rv electrical set-up.

If I was to run new wire I could use 12/3 or 14/3 with copper ground the - for the 12v system though the frame and the red wire as the positive. The 110v would run black and white as normal
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Old 11-30-2015, 09:18 PM   #2
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I was originally hesitant to use solid copper wire like romex in the trailer, but it turns out that is what is run for the 110 as it is. I don't understand why 12v would be any more prone to damage by vibration
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Old 11-30-2015, 09:36 PM   #3
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I am pretty sure you shouldn't ground the AC 120 v to the frame, a serious accident that could be fatal waiting to happen.


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Old 11-30-2015, 10:20 PM   #4
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Originally Posted by mmeyer View Post
I am pretty sure you shouldn't ground the AC 120 v to the frame, a serious accident that could be fatal waiting to happen.


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Old 12-01-2015, 09:17 AM   #5
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This sure is one interesting idea. Unless I am completely off my rocker, ground is ground. The house AC wiring ground is connected to a big copper stake in the ground. It used to be connected to the water piping before the advent of the plastic piping. The trailer frame is connected to the ground by stabilizers, although that is not a very reliable connection. Floating trailer ground is not good I experienced it once and recently posted about using a two conductor extension cord - a nono.

I suspect that mixing 12V and 115V in one cable might violate some codes, if they are applicable to the travel trailers. Some other people might know better.

Another thought is that the proximity of those systems might induce 60Hz ripple on the DC, which might be undesirable.
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Old 12-01-2015, 09:26 AM   #6
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I will have to go check, but I think my AC is grounded to the frame of my trailer, by the factory.
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Old 12-01-2015, 09:45 AM   #7
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Definitely an invitation for 60 cycle hum on anything 12 volt. Short to neutral or ground wire trips a breaker as a safety. Short to 12 volt lights up your 12 volt with 120 volts with danger of fire or electrocution. Not a good idea at all.
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Old 12-01-2015, 09:50 AM   #8
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On some trailers the 12V ground is established through the trailer frame , on others the ground is established through the white wire throughout.
The 120V ground is always established through the supply line. The trailer frame is never a reliable ground and can be deadly.
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Old 12-01-2015, 10:01 AM   #9
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Hi, 12volt D.C.travels on the surface,therefor multi strand wire.AC. travels (electrons) through the whole wire,therefore solid wire.You'll loose some 12volt when using hose wire.Cheers to all m
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Old 12-01-2015, 10:04 AM   #10
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On-board Energy Management Systems won't allow power to flow to the trailer when using a standalone generator unless a bonding wire is present between the trailer and the generator frame bonding bolt, which establishes a common electrical ground voltage level. The AC ground is the frame on Escape trailers, which have to meet the US and Canadian electrical codes.
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Old 12-01-2015, 10:27 AM   #11
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You cannot mix voltages or systems in the same cable or raceway. If the conductors are damaged or shorted you could end up with 120 VAC impressed on the 12 VDC system.
What you are suggesting is a violation of the NEC , unsafe and a good way to get someone killed. If your only goal is to save money ,have at it. Why do you think RV manufacturers do not do what you are suggesting, especially if it would cut costs???
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Old 12-01-2015, 10:43 AM   #12
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Originally Posted by steve dunham View Post
You cannot mix voltages or systems in the same cable or raceway. If the conductors are damaged or shorted you could end up with 120 VAC impressed on the 12 VDC system.
What you are suggesting is a violation of the NEC , unsafe and a good way to get someone killed. If your only goal is to save money ,have at it. Why do you think RV manufacturers do not do what you are suggesting, especially if it would cut costs???
Unless all of the conductors are insulated for the highest voltage present, I believe.
NEC code [300.3(C)(1)].
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Old 12-01-2015, 11:07 AM   #13
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Unless all of the conductors are insulated for the highest voltage present, I believe.
Years ago that was true but not now. We used to put the 12 volt controls for central air conditioners in with the power wires for the A/C by using 600 volt wires for the control wires .
That is no longer legal . Plus the bare wire in a romex is an equipment ground not a current carrying conductor. There are so may code violations and unsafe things in what the OP is suggesting that it would take days to list them all. Bonding and grounding are not synonymous and its obvious that many do not understand the difference . Endangering lives to save a few cents is a poor bargain IMHO
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Old 12-01-2015, 12:23 PM   #14
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Low voltage is NEVER allowed in the same conduit as high voltage. Even an accidental short could really reek havoc and blow stuff up. When you use shore power the camper is grounded to earth by your power cord. Look inside your converter sometime and you will see that is it all separate. They use a common ground on the case but the "HOT" wires are totally isolated so they may never touch each other.
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Old 12-01-2015, 12:27 PM   #15
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Originally Posted by tractors1 View Post
On-board Energy Management Systems won't allow power to flow to the trailer when using a standalone generator unless a bonding wire is present between the trailer and the generator frame bonding bolt, which establishes a common electrical ground voltage level. The AC ground is the frame on Escape trailers, which have to meet the US and Canadian electrical codes.
A ground is supplied to the frame of the trailer in case a hot wire contacts the trailer frame it is not THE ground , the ground remains the supply line .
In the case of a generator a GFI comes into play .
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Old 12-01-2015, 12:39 PM   #16
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Originally Posted by cmartin748 View Post
Low voltage is NEVER allowed in the same conduit as high voltage. Even an accidental short could really reek havoc and blow stuff up. When you use shore power the camper is grounded to earth by your power cord. Look inside your converter sometime and you will see that is it all separate. They use a common ground on the case but the "HOT" wires are totally isolated so they may never touch each other.
All wiring must be of the category CAT 1, 2, 3, etc. as the highest voltage in the raceway or conduit.
Personally I ran separate wiring for all of my new installation from the converter more for future troubleshooting than anything else.
However there is no code violation in doing so as long as the above is taken into account.
You will find that with A/C wiring the thermostat wiring is CAT 2 and the power is CAT 1 so they cannot be run together and meet code.
Usually in A/C equipment the wiring from the thermostat wires to the contactor after the terminal strip is insulated for 600 volts and is not cat 2.
I would not consider running the 120 volt AC with the 12 volt in Romex more for keeping the system simpler to troubleshooting and those pesky solid copper wires from breaking.
The separate wiring should (in fiberglass and most other trailers) have a separate ground wire run along with the feed wiring again for easire troubleshooting.
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Old 12-01-2015, 12:53 PM   #17
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Running Romex 14/3 with red wire as 12+

I would not run 14/3 wire, then use red as DC and black as AC. I think that the AC runs one place and the DC runs another place.

Here are some simple things to think about though.

The frame is a good thing to use as a bonding point for ground or negative of the battery. Problem with these fiberglass units, you will have to go in and out through the fiberglass. For all of your items inside, I would use a terminal strip with a heavier wire and attach it to the frame rail bolt.

DC is simple - negative is used as the ground reference, and the positive is the feed to the equipment. You can switch on either side using the positive or the negative.

AC is where you have to be very careful, electrocution is possible if not done correctly.
  1. in the AC panel the neutral is NOT to be connected anywhere to ground.
  2. the ground wire is to be connected to the metallic case and then to the main metallic part of the coach - the frame.
  3. If you are running a generator, you have to make sure that the neutral and ground is connected AT the generator.
When making the AC connections, one has to be careful that the ground and the neutral is not making contact in any of the receptacles. If you do not have a meter, it is best to get one. There should not be any continuity between the neutral and ground when checking at the plug end of the system, that is if nothing is plugged in.


The code states that you are allowed to only have one GROUND point. In steps 1 and 2, the ground point is the post/grid at the building where the power is coming from. In step 3, the ground point is at the GENERATOR.
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Old 12-01-2015, 03:19 PM   #18
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All boats, airplanes, cars, trucks, campers, etc. should have stranded wire for both 12V and 110ac, unless you want to deal with eventual fatigue of the solid wire. I know, the RVIA approves solid wiring (CHEAPER) in building the cheap (but pretty) stickies for their short life. Many have not had issues, but I would rather spend a bit more and do it right. Others were also right about not running low and high voltage together.
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Old 12-01-2015, 03:42 PM   #19
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As large a problem is the insulation over time. If SO cable is used with it's stranded wire the larger problem might be insulation breakdown.
If the romex is used then the proper clamping in the bos should be used. With the length of unsupported wire short there would be little vibration and thus breakage.
I have seen a lot of poor wiring where the things look like a true rat's nest of loose wires.
Here is a picture of the loose 12 volt wiring in my Scamp.



All of the wiring needs to be laced up to limit flexing.
While I am using the converter and it's power distribution system for the 12 volt systems I have a breaker box installed in the left kitchen cabinet with ground fault breakers. All of the 120 VAC wiring in my trailer is romex with the proper mounting boxes and clamping to stabilize the wire.
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Old 12-01-2015, 03:51 PM   #20
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