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Damsel in Distress, Needs 12v DC LED lighting help... Answered


I am converting a 20' shipping container into a cabin. I have an electrical panel that houses both
AC and DC. http://www.progressivedyn.com/all_in_one_pd4000.html
What I need to know is what gauge wire to use for the DC lights. (plugs will be AC)
I am using 12V DC lights:
I understand the basics  of wiring but need to know the type and gauge of the wire to use. The longest run of wire will be max 25 feet.
I believe I would use red and black wire as that is what is wired into the lights and transformers.



2 years ago

How many lights are you of the 12V DC lights are you putting in the cabin ?

Hello, thanks for your email.
I will have 8 LED puck lights 3w SMD5050
one 2w LED wall light
one 3w corn light pendant lamp
a lighted mirror with 4 2.5 corn LED light bulbs and
a 5M 50LEDs DC12 copper wire string light
to be exact!
I have had different opinions on what kind of wire to use.
I have been told 14/2 would work and also 18 gauge black and red.
If you could clarify that would be very helpful.

So the puck lights 12v version are 8x3 = 24W

A 12v wall light and corn light ........ 2+3 = 5W

Four mirror corn lights .............. 4x2.5 = 10W

Even though the 50LEDs are 12v they run off of an 110v adapter.


Worst case you have 39 Watts at 12 volts means 39/12 = 3.25 amperes

If you use 14/2 gauge two wire o.005 ohms per foot x 25' = o.125 ohms

Worst-Case Voltage drop o.125 x 3.25 = o.41 volts if everything is turned on at the end of your 25' wire. This Is Acceptable as the lights are distributed along the line and I assume the LEDs will rarely all be on at the same time.

Go for it with 14/2 :-)

BTW if you really wanted to pay for the heavy 12/2 wire you would only save o.15 volts worst case.


Thanks, I actually bought both 12/2 and 14/2 with the intention of doing 14/2 for the shorter runs and 12/2 for the the runs to the opposite side of the container. Then I started to get different opinions. If there is more than one way yo skin the cat, I will likely stay with my original plan as I already have the materials.

Thanks again

Good for you, ......... Anyway I saw the start of Romax cabling.

You may want to consider putting nail stops to avoid worry about putting a sheetrock nail through a wire :-)

Click the pic to see it all.


AWG wire sizes are confusing (to me) because they are based on a peculiar
kind of mathematical voodoo. For this reason, a table, like this one,


is helpful for turning AWG numbers into honest physical parameters, like diameter, and electrical resistance per unit length.

I think the
first step is the realization that long wires look like resistors
. For
example, a wire that goes 25 feet, then comes back the same distance,
has a total length of 50 feet. Supposing this wire is size 22 AWG, (per DU35m's suggestion) its
resistance per unit length, from the table linked above, is 16 milliohm
per foot, times 50 feet, equals 800 milliohm, or 0.8 ohm; i.e. R = 16
mohm/ft)*(50 ft) = 800 mohm = 0.8 ohm

Next, consider the
amount of current flowing through this long wire. I would guess LED
strip lights want maybe around 1 ampere. So the voltage drop across the
long wire is V = I*R = (1 ampere)*(0.8 ohm) = 0.8 volts.

reason you care about that voltage drop is because it is reducing the
voltage seen at the load, which, in this case, is now only 12.0 - 0.8 = 11.2 volts,
rather than the full 12.0.

So the game with long wires, is
basically to design them so they only eat a small fraction of the total
supply voltage, in this case 0.8 volts, out of 12.0.

Generally speaking, the other part of
the game is considering the actual heat (in watts) generated by the long
wire, I^2*R (eye-squared arrrr...), in this case (1A)*(1A)*(0.8 ohm) =
0.8 W. However that heat is distributed over this long skinny thing,
about 8 meters long, and that is 0.8 W/ 8m = 0.1 W/m = 10^-3 W/cm ...
Well, actually, I should probably be thinking in terms of power per
surface area, e.g. units of W/cm^2. I dunno. I don't think the wire is going
to get noticeably warmer, which is what those ratings for ampacity,


are all about.

Thank you,

I had found this chart:


I think I prefer the table in the Wikipedia article for "AWG". It has more numbers in it.

Anyway, after reading over everybody's suggestions for your 12 volt wiring, I think I'm going to recommend 18 AWG, 2-conductor, lampcord, for your LED lighting, and other loads that draw less than 5 amperes or so.

The kind that is colored red and black looks pretty, or at least it makes it easy to get the polarity right. I saw some here,

and I found that link via a Google(r) search for "18/2 lamp cord" .

Regarding the ends of stranded copper wire, like typical lamp cord or speaker wire, if you solder just the end, like the last 1cm, this is a trick to make it solid, just at the end, and this is convenient for connecting it to some things. For example, a straight (exclamation point shaped) end is good for connecting into wire nuts. A hook (question mark shaped) end is good for putting underneath a screw.

Of course you can put bare, stranded, copper wire into a wire nut, or under a screw terminal, but it tends to get kind of shredded if you have to take the connection apart and put it back together more than a few times. Although, if you can get everything right the first time, maybe there'd be no need to take it apart later.

Soldering wire to make it solid is a very bad idea. Solder creeps, especially the new stuff. You can solder solid for temporary work, but its a serious no-no for real work. Major fire hazard

Awww, but tinned copper looks so pretty! So what should I be using for making the ends of stranded copper become more solid? Like crimpy lugs, or what?

Yes, crimps are the way to go for stranded conductors, or screw terminals, or Wago clamps, but not wire nuts...

I won't be hooking up the wires I will just be putting them in place, I will have someone who knows what they are doing connect them. Doing the container is not as straight forward as 'normal' construction as it is more like piecework, as I don't want to be calling them every 5 minutes to come and put another wire in place! Thanks.

For those short distances and DC normal speaker wire should do the trick.
22AWG should be plenty and being flexible it makes installation easy.
It comes cheaper than dedicated ligthing cable and is easier to handle as those lighting cables are mostly for outdoor use.
I use the stuff for all my DC needs unless I have a demand for real amps like on a fridge or car amplifier.

Thanks for your input,

What kinds of things are you running when you wire for DC? I will be using just LED lights. 22awg seems a bit small...

Where are you?

I live in Ontario Canada.

Where I live at over 108 square feet and not on wheels it will need to pass code even for a cabin or a gazebo, in fact you need a building permit. So at the back you should put in a window or door for ventilation and a fire escape, if you put in a window it should be large enough for a person to get out through it in an emergency.

Hooked up to service on wheels or not must pass code where I live. Under 24 volts is outside code jurisdiction where I live so I would use #16 braided wire however if you must pass code #14 is minimum in most places. # 14 is larger than #16.

I live in BC, as long as the structure is portable I get around all the by-laws. If they come and say you need to move that, and we can, no worries...

Big difference here no wheels pay taxes and if it has wheels must be in a trailer park even if you only live in it on weekends or hunting trips.