Question about appropriate wire gauge

I sort of posted about this before but wanted to start a clean thread about it.

I’m hoping to clean up and finish installing wiring to pos and neg distribution blocks, and an aux fuse box, all under the hood, and running 12v power to the bed to a second aux fuse box to which I’ll be connecting my fridge which pulls ~9 amps. I’m not sure what else I’ll be connecting to the fuse box located in the bed, but I’m thinking air at some point and figure I may as well leave room to grow.

What gauge wire should I use to run power from the battery to the dust blocks and on to the bed mounted fuse box? LMK if more info is needed.

 

8 gauge, same as the battery cables works for me.

 

what is the distance of the run ? that makes a difference I beleive

 

Size the wire you are coming from(fuse box), then run the same to your new box. You will be able to handle what ever you like at the new box. Larger wire is always better and safer. Found this if you are interested.

https://www.altestore.com/howto/wire-sizing-tool-for-12-24-and-48-volt-dc-systems-a106/

 

It’s always fine to go bigger, but it’s never fine to go smaller.

It depends on length of the run but for most applications on a truck, that length factor is overall pretty small in scheme of amp ratings.

It also depends on how many accessories you plan to run but mainly depends on the amp rating of your aux fuse block. For example if it’s a Bussman and rated at 80a max, id probably run 4awg.

So we all understand it straight, it sounds like you want a single wire going to a distro block and then 2 wires coming off that, 1 going to the engine bay aux panel and one to the rear. Is that right?

 

Not sure which cables you're talking about, but the factory ones coming off the batter are 2 ga iirc

Yes, distance matters a little bit. As does surge (or startup) amperage

As JdevTac said, always better to go too big.
See the chart below for some better info
http://www.offroaders.com/technical/12-volt-wiring-tech-gauge-to-amps/

 

Good point. I forgot to mention I got the limousine option...

 

Thanks that’s what I needed

 

Thanks that’s helpful too

 

This doesn't directly answer your specific question, but just want to remind that there a few items that go into it:

Aviation guy here, so all my wiring is based on AC 43.13 using 100degC MIL-W-22759 wire...
See Chapter 11, Section 5 (also Section 4),
http://rgl.faa.gov/Regulatory_and_G...9baac81b86256b4500596c4e/$FILE/Chapter 11.pdf

All examples below are based on good (not rubbery shit) wiring insulation

Normally sizing wire requires
Sufficient mechanical strength (use #20 AWG or larger wire, and for smaller wires or wire bundles support more often and shield, use fine stranded wire and be especially careful at solder joints).
Sufficient current carrying capacity for the circuit protection device.
Sufficient wire size to keep voltage drop at acceptable levels.

So normally 2 separate checks are required:
if the wire shorts to ground we want to make sure the fuse blows before the wire gets too hot, melts the insulation and lights the vehicle on fire. The wire will get kinda 'hot' for an instant before the fuse blows, we just need it to not self-destruct.
we want to make sure that the device hooked to the wire will operate correctly without excessive voltage drop in the wire, and the wire getting too hot.

Example, the fancy LED only pulls 1 amp, which requires a tiny wire. But the wire is hooked into a 5 amp fuse which powers a bunch of separate LEDs. The voltage drop check will not be critical for this wire, only the circuit protection check for 5 amps without damage (22 awg aviation wire can handle this theoretically).

For separate example, assume that a 4amp led on a 5 amp fuse. The same fuse condition applies giving 22 awg minimum, but now the voltage drop check at 15 ft long requires 18 awg. (Remember full current path length is critical, although a good ground to frame has pretty low resistance for smaller currents.)

As already stated, larger wire is always acceptable, provided it is mechanically acceptable (with acceptable insulation, strands, etc).

 

Wow this got technical, first reply was good though. The wire needs be large enough to meet your current (power flow, not tense) demands. If its too long or too small it will be too resistant to provide enough power to whats in the bed. If its already mentioned good, if not, make sure you chose an appropriate in line fuse for the items you use and make sure to place it nearer to the battery than the bed.

 

Where space is at a premium, you can pair up 2 smaller wire AWG of the same size to accommodate an overall larger current capacity. The assumption is that both wires sharing a load are connected at the same place at each end, and are equal length.

 

Ok I’m back to this thread after being down for the count for the last week. Never been sick more since having a kid...

So, yes - your last paragraph is what I had in mind. Although now that I’ve thought more about it, would it be better (or at least more organized ) to skip the distribution blocks under the hood and run a sub-fuse box off a circuit from the under hood aux fuse box to dist blocks in the bed?

 

This is great info but it’s making my brain hurt. I’ll have to reread it about a dozen times.

A lot of people have recommend welder cable for it’s flexibility and oil and heat resistance. Any thoughts on that?

 

I personally run a blue sea safety hub 100 like this:

https://www.bluesea.com/products/7725/SafetyHub_100_Fuse_Block

But something like what I’ve got linked below is super simple and just as easy and enables you to fuse directly at the battery which is max safety and also super easy, only issue is sourcing these fuses if one blows, you’d have to buy online probably:
https://www.bluesea.com/products/2151/Dual_MRBF_Terminal_Fuse_Block_-_30_to_300A

You can do this in a variety of configurations with different types of fuse blocks or fuse holders though. Main thing is the fuse/holder is properly rated.

Edit: also welding cable is fine, it’s what I have running to my panels.

 

I ran 6 Gauge Welding cable to the back from the 2nd battery in my dual battery setup. I put in a Low Voltage disconnect to not drain the 2nd battery dead if i forget to unplug fridge or not drive the truck for a long period of time.

 

Connect the battery + to a high amp circuit breaker, then on to distribution with each separate fuse box having it's own main breaker. Anything between the battery and first breaker is unprotected so you want that breaker as close to the battery as possible. Breakers also serve as quick disconnects so you can work on de-energize circuits without disconnecting the battery from other systems.

 

I was thinking of implementing the fuses in your second link. No biggie on sourcing the fuses. I’d just order extras to carry.

 

That’s a good idea. Which low voltage protector did you go with?