Noob camper system build, help :)

[robbob2112]

Me too.

Of course it is. An 0 is 53.5mm^2 and 4/0 (0000) is 107mm^2 cross section area

 

[justinm001]

Of course it is. An 0 is 53.5mm^2 and 4/0 (0000) is 107mm^2 cross section area

So the real question. Why is it 4/0 not 4 times as big as 0?

 

[robbob2112]

So the real question. Why is it 4/0 not 4 times as big as 0?

4/0 means awg 0000.... not a multiplier

 

[SoggyShoes]

So the real question. Why is it 4/0 not 4 times as big as 0?

In the AWG wire sizing system every 6 sizes is double the diameter and, more importantly, every 3 wire sizes is double the cross sectional area.

If you want to know why or a little history on it read below. ↓ (warning contains math)

The AWG numbering system is based on the number of draw dyes wire makers had pull the wire through to get to the desired size. So #1 wire was pulled through one dye (just to make it round) where #36 wire meant that it was pulled through 36 dyes. This process is believed to have been done since the time of the Romans.
Over the centuries it was figured out that reducing the diameter of the wire by about 11% per pass by pulling the wire through the draw dyes was the maximum amount to safely reduce the wire size without risk of breaking the wire. This amount is the basis for the AWG wire size used today. The diameter of each higher AWG wire number is (rounded) to 11% smaller than the previous larger wire size (but smaller wire number). So number #36 is 11% smaller than #35 which is 11% smaller than #34 and so on.
This makes wire sizing an exponential function. A shrink (or decay) rate of 11% means the decay factor is 1-0.11=0.89. Then the doubling size (gauge), g, is 2=0.89^g ⟹ g=ln(2)/ln(0.89)≈-5.95≈-6 gauges. So every 6 wire sizes (down in AWG number) have twice diameter.
Unfortunately, with the exception of fitting a wire in a terminal, we don't really care about wire diameter. What we care about is the wire's cross sectional area (given the same wire material and insulation). Area of a circle is A=π*r² where the radius, r, is half the diameter, d, so A=π*(d/2)². Solving the equation representing the number of wire sizes to go up to double the cross sectional area of the wire means with the square in the area formula turns into half when using logarithms to solve. So half of 6 or every 3 wire sizes up, doubles the cross sectional area of the wire. Thus, as @ericfx1984 pointed out, AWG 0000 or 0/4 wire has twice the cross sectional area as AWG 0 wire

Whats the deal with the 0000 wire or "ought" wire numbering?
Well here you go....
With the rise of the modern electric motor (and the telegraph and industrial revolution) there was a need for bigger wire (which was not the case when wire was mostly used for jewelry and and some construction). The rise of the electric motor and the industrial revolution also increased the capacity to make wire bigger than size #1. The wire manufactures decided if #36 was the smallest wire (at the time) and #1 was the biggest wire, the next wire bigger than #1 should be #0. Soon, wire bigger than #0 was needed. It would have been better mathematically to make that next size bigger -1, but the wire makers chose to follow the grain milling numbers and use 00 called "double ought" for double zero. This pattern continued until wire size 0000 or "ought-four" for four zeros. Somehow the notation 0/4 came into play for 0000 representing how many zeros or "oughts" represented the wire gauge size.
This was all formalized in 1857 when it was decided by 8 of the major US wire manufactures to adopt the current AWG (or American Wire Gauge) wire sizing. Where wire size would be determined by the exponential function where AWG 0000 (or mathematically -3 wire) would be 0.46 inches in diameter and AWG 39 wire would be 0.005 inches in diameter.

 

[ericfx1984]

I thought 4/0 was shorthand for 0000

It is

 

[ericfx1984]

Me too.

It is... I wasn't suggesting otherwise

 

[HarryN]

deleted

 

[drumguy]

Thanks for the discussion, I'm learning a lot. I been swamped with work and life so haven't stayed current but here is a little more info.
Camper is an 17' 1980s era Shasta tandem axle trailer. While it has a battery charger in it, it is ancient and (I'm assuming) is not going to be up for the task of charging the LiFePO4 batteries without damaging them. The A/C will be run as sparingly as possible. While I can understand the advantages of going 48V, I feel like this build is not the one. My system should be similar to corn18s with short large wire runs.

 

[sunshine_eggo]

Your batteries could power a typical RV rooftop A/C for about 3 hours from full to empty.

Battery voltage is about loads, not the size of the trailer. If you might run 3000-4000W of loads simultaneously, 48V is very viable.

48V has the typical benefits of using lower gauge wires AND you only need to buy half the MPPT output you need at 24V.