For 100 w lights. The cheap lights I bought didn't come with wire. Can I use speaker wire (like 14awg), or should I use solid wire? Which size should I use. Can anyone point me to a good reference site? Thanks

 

You probably want to use stranded wire. It is typically more expensive, but solid core wire is very brittle. Bend it back and forth a few times and it can break. It takes a lot more to break the filaments of a stranded wire.

As for size, current carrying capacity is determined by ambient temperature, insulation, current through the wire and length of the wire run (and probably a couple other things I haven't remembered). For two 100-watt bulbs operating at 12 volts (more realistically 14 volts), the current draw is 16.67 amps (and at 14 volts I'm not certain because it depends what the resistance of the light bulb filaments does as they cool/heat). And, assuming about ten feet of wire, I'd say that you'd be safe with 18 GA, but would build in a safety factor to 16 GA (but, if you have a kit from the mfg with smaller wire, I'd stick with it since they would have properly engineered for all variables, including resistance of the insulation to temperature change).

As for speaker wire: That's typically designed for a home environment. I'd be concerned with the quality of the insulation--will it melt if the wire is lodged against the radiator, for example? I'd stick with automotive hook-up wire with a high quality insulation--and I'd still route it to avoid contact with hot surfaces. Check at your local auto parts store.

 

DO NOT USE SOLID WIRE!

You should stick to either automotive or marine wire. If you want a real easy install you can purchase a complete wireing harness with fuse, relay, and dash switch from a company like KC.

 

For lights you want to use a wire with as many strands as possible because the current is carried on the outside of each strand. The more strands the more power you can get to your lights.

 

For any automotive lighting, use stranded wire. As for the size, Mark pretty well covered it. Let me add since you will be using one feed for both lights, then you will have a total of 200W. The ampicity you will be drawing at 200W at 12 VDC will be about 16.7 if you use the chart for a DC circuit.
(granted the nominal voltage from a good battery with the engine running is anywhere from 12.9 to 13.9, but for practicality a DC circuit at 12 volts will draw a bit more amps then for 12.9-13.9)


COPPER CONDUCTOR AMPACITIES, IN FREE AIR AT 30 DEGREES C
================================================== ======
INSULATION RUW, T THW, THWN FEP, FEPB
TYPE: TW RUH THHN, XHHW
================================================== ======
Size Current Rating Current Rating Current Rating
AWG @ 60 degrees C @ 75 degrees C @ 90 degrees C
================================================== ======
20 -------- *9 ----------------------------- *12.5
18 -------- *13 ------------------------------ 18
16 -------- *18 ------------------------------ 24
14 --------- 25 ------------- 30 ------------- 35
12 --------- 30 ------------- 35 ------------- 40
10 --------- 40 ------------- 50 ------------- 55
8 ---------- 60 ------------- 70 ------------- 80
6 ---------- 80 ------------- 95 ------------ 105
4 --------- 105 ------------ 125 ------------ 140
2 --------- 140 ------------ 170 ------------ 190
1 --------- 165 ------------ 195 ------------ 220
1/0 ------- 195 ------------ 230 ------------ 260
2/0 ------- 225 ------------ 265 ------------ 300
3/0 ------- 260 ------------ 310 ------------ 350
4/0 ------- 300 ------------ 360 ------------ 405




* = estimated values; normally, these small wire sizes
are not manufactured with these insulation types

There is meaning in the letter sequences used to identify conductor types, and these letters usually refer to properties of the conductor's insulating layer(s). Some of these letters symbolize individual properties of the wire while others are simply abbreviations. For example, the letter "T" by itself means "thermoplastic" as an insulation material, as in "TW" or "THHN." However, the three-letter combination "MTW" is an abbreviation for Machine Tool Wire, a type of wire whose insulation is made to be flexible for use in machines experiencing significant motion or vibration.


You can see on the chart that although 16 gauge will most likely cover the amprage draw, the insulation may not be of the type reguired.
For my aux lights of 100W each, for a total of 200W, I use and would reccomend 14 gauge THHN or MTW. This will insure that when you fuse the circuit up to 20 amps, the fuse will blow before the wiring has a chance to melt.
In addition I do not reccomend using a switch for the power, but rather for the control circuit to a relay with contacts capable of handling the ampicity the lights will be drawing.

 

Solid THHN wire is for use only in commercial and residential structures, not automotive purposes. Leave teh solid wire in your house, and use stranded AUTOMOTIVE wire froma reputable auto supplier.
There is a big difference in the insulation of the auto wiring, which contains more rubberized compounds to tolerate more extreme temperatures, vibrations and current draws.
Stranded wire can actually handle marginally more current (amps) than a stranded wire because the electrons actually flow across the surface area of the copper, not through the core.
In a past life I was a licensed and insured Master Electrician. 6 cardioversions and a surgery later, I'm still here.

 

Make sure you throw a fuse in line too ;-)