Question about appropriate wire gauge

I didn't write it well, but yes in the situation of a short. I approach it as you mentioned, fuse as a protective measure. The wire will allow more power than people believe though. People run 100w amps thru stock wires, those can see an excess of 20v at the typical 4ohms. The wires don't fail, they do be come too resistant to let the end device see all of the 100Ws though (but not by much). Stock wire is likely 20g or so, I know its not 18g. A stock wire that has 20V supplied at 4ohm resitance is going to see 5A. Even the typical 50w option that most do sees just over 3.5A on the stock 20 or 22g wire.

 

100w audio output is a bit different than the 100w input power. Input power is 12V but high current (8A+)while audio output is low current high voltage so the wire requirements differ. Wires are rated for primarily for current with an upper limit on voltage rather than a specific wattage. Squabbles seem to arise often because of misunderstandings or looking at different aspects while thinking the same one is being discussed. I try to be clear but was never an english major, any corrections I may make of other's statements are solely directed at trying to clarify things that I think are unclear or incorrectly worded. It doesn't mean I'm immune from being wrong or writing poorly or simply misunderstanding someone else.

We're here on the net helping others with stuff that done wrong could have serious consequences, nitpicking on clarity should be the norm. The occasional food fight is another story.

 

And back to this project. If you recall this thread, is this wire suitable:

https://skycraftsurplus.com/122-unshielded-nickel-plated-ptfe-jacket-m27500-12re2u06-rp7110.html ?

 

In my opinion, yeah, that wire would work, but why run two conductors rather than one?

 

So if I am re-reading right.
Plan is about 10 amps on about 30 ft round trip. I assume you are looking at running power and ground with the 12/2 wire. (I dont remember the exact numbers if you gave them)

Fuse it about 15 amps, will be fine for short circuit conditions with the 12 gauge.

Range of recommended gauges would be 14-10 gauge depending on acceptable voltage drop (power loss)

For items running off alternator, 12 gauge would certainly be fine. If this is running off battery you may want to consider going to 10 gauge instead of 12 gauge just to reduce power loss (and slight voltage drop).

With 12 gauge, 30 ft of wire is about 0.06 ohms which will eat about 6 watts (just in wire) in addition to the ~120 watts in the fridge. So that is 5% of power lost. Going to 10 gauge will help a little dropping it to about 3.8 watts. I dont know if that is worth it to you but its something to consider.

One other point. That nickle plated wire is good stuff, but solders VERY POORLY. Nickle plated is great for corrosion and high temp, but horrible for soldering. If you are doing good crimps it will be good, but its not worth trying if you think you may want to solder it.

(For soldering, go with tin plated (ok) or silver plated (better) wire)

 

I don’t know. Should I ground to the frame?

 

I didn’t know about the soldering - thanks. I’ll probably crimp this together but that little bit of info was enough to just tip the scale in favor of running a 50 amp circuit to a fuse box in the bed instead.

Going with this:
https://skycraftsurplus.com/wire/mil-spec-aircraft.html?p=5

As @twolane and others have mentioned, should I just ground the sub fuse box for this install to the frame?

 

Personally, Id run a dedicated NEG wire back. Just for peace of mind. You know that it is rated for the current you plan to push through it, and if you ever have issues you know exactly where to look

 

If you don't want to run a bunch of ground wires back to the battery you could run a single heavy cable and tie your grounds to that with a buss bar, only the hot wires need to be separate and fused separately for wire size. As long as the ground cable can handle the total current you're fine.

 

You don't ground the fuse box, you ground the neg side of each accessory, either to the frame, a return wire to the battery, or to a common buss bar next to your fuse box with a cable to the battery same size as the auxilary fuse box cable.

 

I think long term, you will be happier with a larger sub box, so it's probably worth it to do it more expensive up front.

That 6 gauge wire should be good. I would fuse/breaker it at the battery at 50 - 70 amps or something like that. That tin plated wire will be good corrosion resistance and solderable if needed, and 150C rating is more than ample. It will have good minimum voltage drop for 20 amps or so, so you dont waste battery power heating wires for your fridge, and still carry much more amps if needed, especially with a bit of acceptable voltage drop for short term loads.

Make sure terminals and bend radiuses will be able to handle your intentions, that is some thicker cable and it is almost all copper so even as heavily stranded, it wont super like to bend.

I would personally run a separate ground wire, but it should be acceptable to use frame if you do a good job to protect the ground connection from corrosion long term.

I would personally run the wires in a piece of tubing where you can, to provide some added protection, and allow you to remove the wire easily. Rather than that corrugated crap, I like to use smooth wall polyethylene tubing, or black irrigation tubing, something like that. Much easier to add new wires I think. PEX might work well too, never tried it...

By no means required, just my suggestions.

 

Alot of blue sea fuse boxes include a ground bar in the same molded assembly. I assume that is what OP is thinking of when he asked about grounding the fuse box.

 

Good deal. Thanks again.

 

Yep

 

Don't do this. If you do, each wire must have its own fuse rated for the wires current capacity. If you run wires in parallel from a single fuse rated for the total current and one wire breaks or becomes disconnected somehow, the second wire is carrying 2x what it is rated for.

 

For your ground- you want it to be as short as possible- less risk of failure and truly, the shortest path to earth.