THHN Wire information

[Toytaco2]

I have been trying to read all the threads concerning wire type and am in a state of information overload. Lots of info, but cannot figure out yet what it all means. I need to pull the wires for my build this weekend and have yet to decide what wire is right. Any help will be appreciated.

I will only have 12 volt fixtures wired into my TD consisting of 2 porch lights, 2 fluorescent cabin lights, a fantastic fan and a single fluorescent light in the galley. All of the wiring will be run in the ceiling (or hatch) and no conduit used. I will be using a combination of circuit breaker protected extension cord and GFCI cord for any 110 volt needs (such as my CTEK battery charger).

I just got back from Lowes and see they sell stranded THHN wire in the appropriate gauges and the prices seem OK. What is the difference between this THHN wire and the same gauge wire I get from the auto parts store (I think its usually called "primary wire")? Which is the better choice for my build OR should I use something else entirely? Also, is 14ga wire adaquate for these fixtures or should I go with 12ga.

[Toytaco2]

Maybe I need to simplify my question: Is the stranded THHN wire sold at the big box stores a good choice for 12 volt wiring or is the automotive type wire a better choice?

[mikeschn]

I don't know what stranded THHN wire is... got a good close up picture of the end of the wire?

I used some really heavy automotive wire to get from the battery to the fuse block.

From the fuse block to the lights, etc, I used a reasonable wire I found at Home depot... I think it was called sound and security wire. It looked like the top wire in this picture.



Mike...

[Ken A Hood]

I think it's "tinned" stranded wire. It's commonly used in marine applications, where moisture/corrosion is a concern.

[TPMcGinty]

I found this about THHN wire:

THHN: Thermoplastic Insulation (usually PVC), High Heat Resistant (90°C rating), dry locations only, Nylon jacket

[tinksdad]

I found this about THHN wire:

THHN: Thermoplastic Insulation (usually PVC), High Heat Resistant (90°C rating), dry locations only, Nylon jacket

DANG NAB IT!!!!! Just got done today running all my wiring with surplus off the spools in the store room at work. Better check it before I close up the roof to see if it needs to be replaced!!!

[TPMcGinty]

I found this about THHN wire:

THHN: Thermoplastic Insulation (usually PVC), High Heat Resistant (90°C rating), dry locations only, Nylon jacket

DANG NAB IT!!!!! Just got done today running all my wiring with surplus off the spools in the store room at work. Better check it before I close up the roof to see if it needs to be replaced!!!

If you seal the Tear right, it should be dry. Right?

I used wire that they threw away at work. Mine was Gasoline Resistant so I thought it should work.

[tinksdad]

Mine is stamped Gasoline and Oil Resistant.... so I should be fine!!! It's amazing what they throw away at work and don't even realize they are throwing it away!!!!!

[Sparksalot]

I just got back from Lowes and see they sell stranded THHN wire in the appropriate gauges and the prices seem OK. What is the difference between this THHN wire and the same gauge wire I get from the auto parts store (I think its usually called "primary wire")? Which is the better choice for my build OR should I use something else entirely? Also, is 14ga wire adaquate for these fixtures or should I go with 12ga.

The big difference between the THHN and the parts store wire is the insulation. THHN is good to 600 volts, the parts store wire probably isn't. They are both acceptable for a tear.

For size, 14 AWG THHN is good for 15 amps of load, #12 for 20 amps. Both are probably overkill for a few lights on 12 volt circuits.

Something to consider here is the flexibility of the wire, especially if any is loosely routed and subject to vibration over time and travel. The automotive hookup wire will be better suited for this.

BTW, my 12 volt system is using S-video cable, which will give two complete circuits for a given length of cable. It's very flexible with fine stranding. If memory serves, it is 18 gauge conductors. I was able to find a 100foot spool of the stuff for $39.

[davefullmer]

Another good source for wire is your local industrial supply stores. These stores sell wire, etc for use in manufacturing plants and other industrial uses. I just checked prices yesterday on some wire I needed and found 3 different prices for the same thing. On 12 ga THHN the local suppliers ranged from $60 to $85 per 500 ft roll at 3 places. So it pays to shop around.

I buy a lot of THHN wire and also MTW wire for use in machine wiring. AS mentioned in an above post, the THHN and the MTW is a quick description for the insulation. There are slight differences in temperature ratings and also how stiff the wire may be. I like to use MTW in the machines because it is much more flexible and doesn't retain the coiling. It just lays straighter in the machine and is easier to make a neat layout.

Regarding the requirement for use in a Dry Location, my opinion is that any wiring that might be used in Wet locations needs to be routed in weather proof conduit and enclosures. For all practical purposes any wiring done on a tear drop would be in a dry location. I would not recommend leaving any wire exposed underneath the chasis.

Dave