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Author Topic: 12v wiring  (Read 3585 times)
Devin & Amy
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« on: July 12, 2006, 08:12:26 PM »

Hi all,

O.K. tomorrow is the 12v wiring day. mostly finished the 120v today. Mr Meyers has been a great help, but I have a couple other questions.

Do I have to keep the physical location of the chases 120/12v completely seperate, a couple of inches apart, or can I run them in the same conduit?

I have a big spool of neoprene 12-2 +G  extension cord wire that i picked up cheap. Can I use this for 12v also? or should I use 12AWG lampwire?

Longest run will be about 30 ft. but will only have 3 lights on it, What size do you think?

Thanks for your help.
Devin
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« Reply #1 on: July 12, 2006, 11:21:05 PM »

Devin, while it's probably fine to run AC and DC in the same conduit (AFAIK), you would want to make it obvious what's DC and what's AC. Not just obvious to you, but to anyone that works on your rig in the future.

Truth is, extension cord wire isn't rated to be enclosed in conduit... for either DC or AC service. It's meant for temprorary, exterior-type applications where the jacket is exposed to free air.  Plus, the ground wire would make most folks think it's an AC circuit. THHN or similar would be applicable. CHeck you lamp cord, becasue it might not be, either.

Also check your voltage drops for whatever loads you're placing on them (remember to do a "round trip" calc. for DC). Here's a nice one online: http://www.nooutage.com/vdrop.htm

For minor loads, 12AWG is sufficient. No sense going much below that, IMHO, because even moderate loads will suffer some voltage drop.

Wire is cheap in the grand scheme of converting. Fires and/or electrical woes... are not.

My $0.02,
Brian Brown
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Brian Brown
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Nick Badame Refrig/ACC
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« Reply #2 on: July 13, 2006, 02:25:19 AM »

Devin,

Quote from Brian:
Truth is, extension cord wire isn't rated to be enclosed in conduit... for either DC or AC service. It's meant for temprorary, exterior-type applications where the jacket is exposed to free air.  Plus, the ground wire would make most folks think it's an AC circuit. THHN or similar would be applicable. CHeck you lamp cord, becasue it might not be, either.

This is the truth, Service extention cords eat up current too. I have a space heater that draws 13.2 amps plugged into the wall. When I used a 30' service cord with that same heater, it drew 14.9 amps and the cord was heating up...

My 4 cents [inflation]
Nick-
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« Reply #3 on: July 13, 2006, 04:24:03 AM »

Nick, I wonder if you did the same test using some other type cord or cable of the same guage and length, plugged into the same outlet? Did you test the current of the heater with it plugged directly into the same outlet?

You indicate that the cord was getting warm. This is an indication that there is enough  resistance in the cord to cause the heating. This is  typically caused by the conductors being too small a guage for the current being conducted. 

In all the electrical training I have had, added resistance in a series circuit will decrease the total current, not increase it, all other things being equal. Inquiring minds want to know. LOL
Richard


Devin,
This is the truth, Service extention cords eat up current too. I have a space heater that draws 13.2 amps plugged into the wall. When I used a 30' service cord with that same heater, it drew 14.9 amps and the cord was heating up...

My 4 cents [inflation]
Nick-
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JackConrad
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« Reply #4 on: July 13, 2006, 04:27:14 AM »

Devin, while it's probably fine to run AC and DC in the same conduit (AFAIK), you would want to make it obvious what's DC and what's AC. Not just obvious to you, but to anyone that works on your rig in the future

It is my understanding that it is OK the run high and low violtage wire in the same conduit as long as all the wire meets the standards for the highest voltage present and as mentioned the wires should be well labeled.  Jack
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« Reply #5 on: July 13, 2006, 04:43:07 AM »

Richard,

Quote:In all the electrical training I have had, added resistance in a series circuit will decrease the total current, not increase it, all other things being equal. Inquiring minds want to know. LOL
Richard


If the cord is stealing resistence, How would that decrease amp drawl at the panel???
Yes Richard, The heater it'self doesn't have a meter in it, LOL   so I took my readings from the panel. I think you have your Amps and Current mixed up. LOL

Nick-
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« Reply #6 on: July 13, 2006, 04:47:19 AM »

Exactly the opposite Nick. The cord is adding resistance in a series circuit. The cord is one resistance and the heater is the other. When you put two resisters in series it decreases the overall current. Conversely if you put two resistors in parallel it increases the overall current.
Richard


Richard,
If the cord is stealing resistence, How would that decrease drawl at the panel???

Nick-
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« Reply #7 on: July 13, 2006, 05:28:32 AM »

I don't know what the code says about running AC and DC wires together in the same conduit, but I was under the impression it was not allowed, and personally, I don't think it's a good idea, anyway. DC doesn't need to be in conduit.

For AC, use stranded THHN or TFFN from HD or Menard's.
For DC, use stranded primary automobile wire.

Suggest you get a copy of Waytek's catalog (www.waytek.com). They're located here in Chanhassan and have good selection, prices, and service.

craig


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Kristinsgrandpa
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« Reply #8 on: July 13, 2006, 08:21:03 AM »

  The new (2005) National electric code doesn't cover low voltage(12V). Low voltage is covered by a separate publication and I don't have a copy. The previous NEC 2002 edition said it had to be separated by .5" (1/2') from high voltage unless crossing it at 90 Deg. angle.

Article 400.8 (6) forbids installing extension cord material in a raceway (conduit).

The trouble with extension cord material is twofold, one it is insulated so thick that it doesn't dissipate heat and the other is that eventually the rubber covering gets brittle and cracks open.

Some of the new insulations are great and don't show signs of cracking.   I've had the rubber covering completely fall off, leaving the three conductors in my hand. I'm sure glad they were insulated individually.
I've installed extension cord material in conduit at work but only for short distances for physical protection, and only when told to do so by superiors.

I wouldn't put 12 V and house cables close together for long distances, especilly signal ckts, like wiring to guages on the dash etc.  The DC will have very little effect on the 110V ckt. but the 100 V will probably affect the DC.

HTH, Ed.
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« Reply #9 on: July 13, 2006, 08:29:40 AM »

The best I found was at home depot. They call it speaker installation wire. grey jacket with 2 inside separate insulated wire.  1 blk 1 red easy coded. 14 0r 16 ga. I used 10 ga single wire to feed from source then tapped the 14ga to run to light or application. grounding one side to bus I ran 3 10 ga or 30 amp circuits that provide plenty of power. You probally won't have over 90 amps ligts or 12v stuff.You can also use brake  or trailer wire 2 individual wires in grey jacket. A little larger. The stranded 14ga works good in either.
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DrivingMissLazy
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« Reply #10 on: July 13, 2006, 09:51:12 AM »

I recommend SO cord which is available at any electrical supply house. As many conductors as you need and any guage wire. Individual conductors are insulated separately and the overall cable is jacketed in Neoprene, I think ,and looks similar to heavy duty extension cord, but is rated for most all applications.

I definitely would not recommend plain zip cord without external insulation as is used for speaker applications for example. There really needs to be an outside covering to protect the conductors reom nicks or any other things that might damage it.
Richard

The best I found was at home depot. They call it speaker installation wire. grey jacket with 2 inside separate insulated wire.  1 blk 1 red easy coded. 14 0r 16 ga. I used 10 ga single wire to feed from source then tapped the 14ga to run to light or application. grounding one side to bus I ran 3 10 ga or 30 amp circuits that provide plenty of power. You probally won't have over 90 amps ligts or 12v stuff.You can also use brake  or trailer wire 2 individual wires in grey jacket. A little larger. The stranded 14ga works good in either.
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« Reply #11 on: July 13, 2006, 10:43:44 AM »

The NEC requires that AC  and  DC be in seperate 'raceways'.  The DC wiring really doesn't need conduit but the flex wrap makes the bundels neater.  I used ENT flex conduit to contain the THNN wires for the AC circuits.  I also used THNN for the DC but in split flex tubing from an auto parts store.
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Jerry 4107 1120
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« Reply #12 on: July 13, 2006, 01:31:25 PM »

Jerry, I do not have a NEC handbook so maybe you could look something up for me.
I used to manufacture power conditioners and converters for the large Uninterruptible Power Supply users as well as manufacturers of electronic and electrical equipment. These units were shipped world wide and I was required to have UL listing on all of them.

Back then, UL did not have any requirements for DC voltage below 50 volts. I believe that the lower voltage was not considered life threatening, so I could do the low voltage circuits any way I preferred.

The question is that since UL guidelines are governed by the NEC as well as a couple of other agencies is there any thing in the NEC that addresses low voltage DC. That is voltage below 50 volts.
Richard

The NEC requires that AC  and  DC be in seperate 'raceways'.  The DC wiring really doesn't need conduit but the flex wrap makes the bundels neater.  I used ENT flex conduit to contain the THNN wires for the AC circuits.  I also used THNN for the DC but in split flex tubing from an auto parts store.
Regards
Jerry 4107 1120
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Moof
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« Reply #13 on: July 13, 2006, 03:04:38 PM »

12v and 120v have to be seperated.  I have purchased J-Box's that are rated for low and high voltage, i.e. 110v and phone. (Expensive)  The design of the box provides a near absolute seperation.  The bottom line is they need to be seperated.  I would think this even more important with the vibrations that the bus electrical systems are subjected to.  Over time you could find 110v  finding its way to your 12v.

Good luck.
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« Reply #14 on: July 13, 2006, 04:24:10 PM »

 as I remember from when I was youge!!
if you pass a copper wire through a magnetic field you make elec. in the wire. if you run elec. through a copper wire you make a magnetic field around the wire. so if you run AC and DC together the DC will affict the AC !
as I remember
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« Reply #15 on: July 13, 2006, 06:43:55 PM »

I don't remember where it came from but I know you are not supposed to run low voltage in a conduit with 120 volt wires.  Maybe a city inspector tagged me for that when we had a sprinkler control wire running in a conduit with the outside yard lites but I know you are supposed to keep em separate. If the 120 is in metal you can use plastic for the low voltage or vice versa but you can't run them both in plastic parallel next to each other. Also watch your cross section fill ratios and conductor count in each conduit.  I always seem to want to add something and don't have a large enough conduit ( to dissipate heat ) or already have too many conductors in the conduit ( neutrals don't count ). Just my thoughts.

Melbo
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« Reply #16 on: July 25, 2006, 11:22:12 AM »

Hi all..new here and new to the building process...I understand that it is correct to use stranded wire instead of romex in conversions, I was just wondering the reasons for this...

So much to learn...
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« Reply #17 on: July 25, 2006, 12:52:22 PM »

Stranded is way more tolerent to the flexing that will take place in a moving vehicle.

Stranded is standard in planes, boats, cars and trucks.

Many have reported using romex and securing it well with no problems.

I'm just one of those guys that doesn't like to push my luck, so I used THHN or SOOJ.

Cliff
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« Reply #18 on: July 25, 2006, 08:56:53 PM »

Besides, it's very easy to make a good crimp connection with stranded wire, but not so with solid.

For what it's worth.

Tom Caffrey
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