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Author Topic: Electrical wire size ??  (Read 3220 times)
Chaz
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« on: April 25, 2008, 09:38:32 AM »

Just a quicky question:
  Can I use 14 AWG cord (lamp cord) for my 24 volt lighting? (rope and single fixtures)

  Thanx,
     Chaz
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« Reply #1 on: April 25, 2008, 09:46:42 AM »

Propbably, but how much current do you intend to run through it?

Keep in mind that many RV fires are from the low voltage side, not the 120 volt side. 

I would be concerned about the quality and thickness of the insualtion.
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« Reply #2 on: April 25, 2008, 10:39:03 AM »

Chaz,

   My gut instinct was a probably depending on length and amps so I did some research.

 Quote from one of the engineering calc sites.
"In an electrical systems the conductors should not be sized with voltage drops exceeding 3%."

  Using a calculator from http://www.csgnetwork.com/voltagedropcalc.html
   for 24V dc 14 awg
   I came up with 20 feet @5 amp draw  2.5%drop
  Play around with the calculator

   YLMV    L=length Smiley

     Skip
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JackConrad
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« Reply #3 on: April 25, 2008, 10:55:09 AM »

Chaz,
   When we wired our bus, we used a minimum of 12 gauge wire.  Better safe than sorry. Also use fuses or circuit breakers of the appropriate amp rating to match the wire size.  Jack
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« Reply #4 on: April 25, 2008, 12:12:55 PM »

Thanx guys. Good info! I'm insulating and want to wire some stuff while I'm at it. I tend to overkill allot.  Roll Eyes  I'd much rather be safe that sorry.
 
I'll work with that calc, Skip. I guess I should decide which lights i will be using to be able to figure out the final figure. But I am dead set on using 100% LEDS on all the 24v stuff. I think that will help some.  Won't it?

Thanx again,
    Chaz
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« Reply #5 on: April 25, 2008, 12:37:03 PM »


 Chaz,

    It's all a numbers game............ # of lights and their draw.

   Generally
         LED least draw
         Fluorescent (IF they are not being turned on and off every 2 mins!) ARGGGGGGGGG
         Condecent easiest to find but biggest draw

 Skip
       
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« Reply #6 on: April 25, 2008, 01:17:28 PM »

I would not use lamp cord even though it is cheap.  It is not intended to be covered.  I have also seen old lamp cord with lots of cracks.

I did like Jack and used a minimum of 12 gauge no matter what amperage.  I used 10 gauge for a few circuits like the 12 volt jacks and lights in the bunks where I thought power draw could be high.

I used tinned marine wire that is UL listed mostly from skycraftsurplus.com.  If you don't see the right AWG and color on the web site call them as they have more not listed online.
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« Reply #7 on: April 25, 2008, 01:25:17 PM »

A most useful resource is the "Pocket Ref" by T.J. Glover.  A compact little black book of more than 500 pages.  I got mine at a hardware store.  A table of "Standard Lamp & Extension Cord Current Capacities" says 14 gauge cord is good for 18 amps should be protected by a 15 amp breaker.  The voltage rating of a wire specifies the maximum safe voltage.  Anything less than that makes no difference.  The book also says 1000 feet of 14ga presents a resistance of 2.58 Ohms from which you can calculate the voltage drops.  Keep in mind that when most things (lights, fans, radios, etc.) call for 12 or 24 volts that means 'about' and +/- 20% is a safe operating range.
-RickBrown in Reno NV
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« Reply #8 on: April 25, 2008, 02:51:56 PM »

"I would not use lamp cord even though it is cheap.  It is not intended to be covered.  I have also seen old lamp cord with lots of cracks."

I have seen some not so old lamp cord falling apart too.  Last thing I would use.  I strongly agree with Brian.

Don 4107
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« Reply #9 on: April 25, 2008, 03:23:27 PM »

Hi Chaz,

This link is available in "The Green Book" thread under Board Help Section on the front page.

It's a very easy table/chart for 12v dc wire sizing

http://www.engineeringtoolbox.com/amps-wire-gauge-d_730.html

Nick-
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« Reply #10 on: April 25, 2008, 03:55:02 PM »

Hey, thanx guys!!! I'll take your recommendations and run with it!!

  Chaz
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« Reply #11 on: April 26, 2008, 08:10:01 AM »

Not to hijack the thread and not directly on the subject, but while we're on "wire" I thought I'd post this photo of a little test I did a few years back for the BNO folks, regarding the use of solid vs stranded wire.
  I did a very informal test, took various wire styles and clamped them in my mill vise and a drill chuck, and bent them up and down all the same distance etc, until they failed.  Quite interesting, and to me says "For busses and where wire gets wiggled alot, use stranded, and the finer the strands the better".  Of course those in the electronics industry already know this, but the bus folks seem to argue it over and over and over. 
 The picture says a thousand words...



« Last Edit: April 26, 2008, 08:15:05 AM by boogiethecat » Logged

1962 Crown
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« Reply #12 on: April 26, 2008, 05:52:12 PM »

No arguement from me! Wink

Great test.

I have always used stranded in everything but a house. It takes a lot more abuse, vibration etc. Really, it is just logical if you think about it. Also securing it ends up with a better result for the long term. Still need to check the terminal connections at least once a year, make sure they are good and tight. Gotta keep the smoke in.

Thanks for sharing that.

Paul
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Blacksheep
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« Reply #13 on: April 26, 2008, 06:43:13 PM »

Not to dispute anything everyone has said but there is a stranded wire that looks like lamp cord but isn't. It's actually used fro outdoor lighting like around gardens and sidewalks. To me, it looks like lamp cord but I think it is better than that! I have used it for my 12 volt water pump and it hasn't failed me yet and doesn't show any signs of failure either.
Just another consideration other than lamp cord!

BS
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« Reply #14 on: April 27, 2008, 05:42:47 AM »

When I bought Noma outdoor lights, the wire that looked like lamp cord had quite a thick insulation but was low voltage wire (not for 120 vac).
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Blacksheep
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« Reply #15 on: April 27, 2008, 06:00:07 AM »

Stan I thought he mentioned he wanted to use it for 12v! I would never use it for 120

BS
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Chaz
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« Reply #16 on: April 27, 2008, 07:49:43 AM »

Actually, 24 Volts.
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« Reply #17 on: April 27, 2008, 10:59:29 AM »

SORRY, but even so I think it would work ok!


BS
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Barn Owl
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« Reply #18 on: April 27, 2008, 11:06:06 AM »

I found this interesting:

http://users.cwnet.com/~thall/fredhobe.htm

Way to save money on wiring by Fred Hobe:

     I buy 100 foot extension cord when they're on sale number, 12/3 conductor wire size. I can get them for as little as $15.00 and they come in different colors. I get several different colors and use yellow for air conditioners, orange for lights, black for wall plugs (120 volt) and green for 12 volt. They are UL approved and very flexible. You need to tin the ends when you hook them up to your main and on other connections use High lugs. Use an indent sqeezer to make good connections. You can buy 100 ft. cords with plugs on them cheaper than you can buy the wire by the foot. I use about 500 ft. of wire on a coach.


This shows how wires are run in the roof. Run them were they will come down the wall to the fuse panel.
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« Reply #19 on: April 27, 2008, 12:48:12 PM »

     I buy 100 foot extension cord when they're on sale number, 12/3 conductor wire size. I can get them for as little as $15.00 and they come in different colors. I get several different colors and use yellow for air conditioners, orange for lights, black for wall plugs (120 volt) and green for 12 volt. They are UL approved and very flexible. You need to tin the ends when you hook them up to your main and on other connections use High lugs. Use an indent sqeezer to make good connections. You can buy 100 ft. cords with plugs on them cheaper than you can buy the wire by the foot. I use about 500 ft. of wire on a coach.
...
This shows how wires are run in the roof. Run them were they will come down the wall to the fuse panel.


Fred's a nice guy, but someday he's going to kill somebody with this.  I've taken him to task for this before, and I wish he would take this deadly advice off his site.  (He's also got air brake advice on there that is similarly dangerous and illegal.)

For the record:  Using extension cords this way is dangerous and also illegal.

Saying that extension cords are "UL Approved" might mislead someone into thinking that makes them safe to use as Fred advises.  In reality,
  • Any UL listing immediately disappears once you modify something, such as cutting the molded ends off an extension cord.
  • Cords are not "approved" they are "listed" for a specific use.  Usage of extension cords is well defined in the listing standards, and these specify that the cords must not be covered in any way, such as installing them within walls, under carpets, etc.
  • The manufacturer's rating for the cord and choice of insulation materials assumes that the cord will be used in the open, not covered.

I've written extensively on this board and even in BCM about why doing this is a fire waiting to happen.  If you care about yourself and your passengers/loved ones, you won't use them.

(Low voltage use, which the NEC defines as below 30 volts, is a different subject.)

-Sean
http://OurOdyssey.BlogSpot.com
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« Reply #20 on: April 27, 2008, 01:08:30 PM »

I was hoping to get the skinny on that, I have always wondered what the reaction would be. For some reason I have not seen other postings on it, it must have been before my time.

Sean, I am always amazed at your depth of knowledge on so many topics. I greatly value your contribution to this conversion community. I also think you have one of the best blogs going. For those who haven’t been there, check it out:

http://ourodyssey.blogspot.com/

Love the videos!


Thanks,

Laryn
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« Reply #21 on: April 27, 2008, 02:17:38 PM »

I was at Home Depot today buying caulk and I looked at the landscape wire.  It 39 cents a foot for 100 feet of 12 AWG.  It would certainly work, but I would still do the marine wire even at 60 cents per foot.  Far less expensive to do it with marine wire for $20 additional per 100 feet than to spend a lot more later trying to find a short or an open, or god forbid having a fire due to bad wiring.
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« Reply #22 on: April 27, 2008, 04:08:35 PM »

Hi Folks,

If this doesn't tell you that Sean is telling you the truth, nothing will!

http://www.magnet.fsu.edu/usershub/safety/documents/extensioncord.pdf

Nick-

P.S. page 4 lays it all out for you...

Disallowed Uses Of Extension Cords
The following uses of extension cords are not permitted at the NHMFL:
• Extension cords may not be used in place of permanent facility wiring. Cords shall not be attached to building surfaces or structural members. They shall not be permanently concealed in walls, ceilings, or under floors - including raised computer floors.
• Do not run cords through moisture, tied to over-head pipes, across traveled roads, under carpets, or across areas of high foot traffic.
• Extension cords may not be run through doors, ceilings, windows, holes in walls, or through hinged door openings in enclosures. This is to prevent “pinch” damage to the cord. If it is absolutely necessary to run an extension cord through a doorway or open window for short-term use, the cord must be protected from damage should the door or window slam shut; it must be removed immediately when no longer in use; and must not be a trip hazard.
• Do not use extension cords that are frayed, cut, or damaged such that inner conductors show, or that have outer sheaths which have pulled loose from their molded plugs exposing the inner conductors. In particular, do not use a cord that has a bare conductor exposed.
• Detachable multi-tap adapters may not be used on extension cords nor on receptacles.
• Cords may not be repaired with electrical tape, nor may tape be used for other purposes on a cord. It may conceal damage, and it does not provide the integrity of the original jacket.
• Do not use extension cords in which the third prong (grounding prong) has been removed from the plug


Other Considerations For Extension Cord Use
Cord overload and overheating:
In addition to the total electrical load, the conditions of use affect extension cord safety. Rated capacity for an extension cord assumes it will be used in an open-air and straight configuration.
As electric current passes through a wire, electrical resistance causes some voltage drop and heating of the wire. Coiling or winding excess cord length can concentrate this heat and overheat the cord. Similarly, covering a cord with a rug or rag can trap heat and overheat the cord. This trapped heat can damage the cord and lead to a fire. Tying a knot in a cord can have a similar outcome.
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« Reply #23 on: April 27, 2008, 05:19:42 PM »

If you don't understand the spirit of the codes or laws, or what they are trying to prevent, you will miss the fact that some things have multiple uses.

Many times an items usefulness is not noted or allowed because another method is preferred or required, and is the code.

Electrical is very much this way.

Lots of good information on this board from many knowledgeable folks.

Read and verify everything for yourself.

Cliff



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« Reply #24 on: April 27, 2008, 08:19:37 PM »

While we're on the topic of wire, in pricing I found 10ga to not be much more expensive than 12. Can to big a wire be bad ? My plan is to use the 10 for everything...
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Sean
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« Reply #25 on: April 27, 2008, 08:44:37 PM »

... Can to big a wire be bad ? My plan is to use the 10 for everything...


Yes, actually.

Oversized wire can certainly be better in many ways -- there will be less voltage drop, for example, and therefore less current draw for induction motors.  Also, it's easier to change circuits out for larger ones, if you need to later.

BUT, there are strict limits on how many wires of each size can go in a conduit or a junction box, and how many connections of each size can be made in a junction box.  Also, devices are rated for connections in a certain size range, which can not be exceeded.

When you use #10 where, for instance, only #14 is required, you will find yourself needing to go to the next larger conduit size in many cases, say 3/4" vs. 1/2".  Or having to use extra-capacity boxes.  And many common household devices such as receptacles and switches are rated for wire no larger than #12, meaning you'll have to pigtail the outlets and make connections, which will again impact the required size of the box.  You may not be able to wire a normal outlet in a normal size single-gang outlet box if you run #10.

HTH,

-Sean
http://OurOdyssey.BlogSpot.com
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