Resistance of Cu tube per foot?

[madlabs]

Hi All,

Got my battery bank set up and charged! My two little solar panels are connected too.

So, I need 12V in my trailer, which is located about 50' from my battery bank. I have 2 options:

1. : I can use the built in 12V system and connect 2 batteries to it. Pro: Easy. Con: I will have to charge it seperately, either dragging my lawnmower/alternator rig over or running my AC generator and using the built in trailer charger. It seems that the trailer batteries will take a greater beating like this.
   
2. : Run 50' of heavy wire. Pro: Even battery wear, easier to charge. Con: Wire is freaking expensive!
   
   

So, I have been trying to figger out if it is cheaper for me to buy wire or use copper tubing to carry the current load I need. I could live with 50 amps max load. The idea is to be able to run a few things that I can on 12V, like phone chargers, my nixie clock and suchlike.

The only resistance table I see for copper tube is for 1/2", Alloy C10200. This is an expensive alloy, I'm sure. What I can't find is a resistance table for regular old home despot type tube. Looking at wire tables, 1/0 AWG is the minimum I could use, with a .505 voltage drop, 4.21% loss. Looking at cable, I see > $2 US a foot. I can get copper pipe for about $1.11 a foot. I'll need conduit for either since I will be burying it, so that cost is the same.

Thanks!

Jonathan

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[ghurd]

Have you considered aluminum USE wire?

Cheaper.  Needs no conduit.  Less effort. Cheaper.

I am not quite convinced it needs to handle 50A with low line losses.

The remote bank will have a bit of lag at high currents, but the high currents will not last very long.  Lower currents mean less voltage differences.

Maybe not be 'perfect on paper' but close enough. Did I mention cheaper?

G-

[Ungrounded Lightning Rod]

There is romex (and equivalents from other brands) that is rated for being buried without a conduit.  The versions I've seen (as of a few years ago) had the outer "armor" layer colored gray and came in a number of gauges and conductor counts.  There is very little premium on the price vs. indoor romex.

(Note that the color may be different now - there has been a move to color code at least indoor romex to indicate its gauge at a glance and that may have been extended to underground rated stuff, too.)

You'll probably want to - and may be required by code to - have a short section of conduit where it enters/leaves the ground.  But that's also good to protect it from trouble, such as weed whips, UV from sunlight, and moisture infiltration at the end where the outer layer is open.  A little hunk of treated 4x4 post with a couple feet of conduit and an outdoor box fastened to it, next to your trailer parking space, seems like a small cost.  You'll want to put the "wires leaving the end of a conduit" cap on the underground end to avoid abrasion against the cut end of the conduit and (if convenient) have a 90 degree bend to start the romex in the right direction for its run.  There are also outlet box covers available that are weather rated even when a cable is plugged in.  You'll want one of those, too.

I don't recommend using buried copper pipe as a conductor.  You'd have to insulate it - especially with it carrying DC - or you'd get KING HELL corrosion on the positive pipe from currents through the ground between the pipes.  The cost of both wire and pipe is mainly the metal.  By the time you got your pipes and their associated stuff installed, buried, and hooked up, you'd be out far more money than if you used underground-rated romex in the first place.

If you do find aluminum wire for your run, be sure to use the proper aluminum-to-copper joints at the ends.  Aluminum wire is a fire hazard (due to the joints becoming resistive with age) and the heating at bad joints is an issue with CURRENT, not voltage, so the fact that you're running less than 120V makes it worse, not better.  A fire in a trailer is more dangerous than one in a house, too.  (On the other hand, a properly terminated aluminum wire run could save a bunch of bux without degrading the instalation's performance or appreciably increasing the fire risk.)

[terry5732]

Why didn't you put your battery bank next to where it would be used?

[ghurd]

Good call.

The proper AL/CU rated connectors were $5 each at one Big-Box store, $5 a pair at the other(Home Depot?).  I think the connectors were rated down to 1 strand of #10.

Maybe $4 for some Ox-Guard.

I figure connectors for CU only would cost about the same.

Lowe's does not have the smaller (1/0) AL around here.

Largest common common direct-bury UV-resistant Romex here is #10.  Costs darn near the same as AL USE-2 #1/0 in 50' quantities.

G-

[ghurd]

BTW, resistance per cubic foot is the same as how long is an acre.

G-

[madlabs]

Well, serendipty stepped in....

My nieghbor had 200+ feet of 1AWG that he GAVE me!! He said he'd had it for years and would never use it. So, problem solved! I'll have to put it in conduit, as it does not appear to be direct burial, but that's cheap!

I didn't put the batteries next to the traler for a couple of reasons. One is security, the batteries are safer in the locakbale container. Another is all the solar panels will go on the roof of the container, so I woul have had to pipe that over eventually as well. Another is sound from the generator, the container makes a good sound break.

CAn you get direct burial romex in large gauges? The largest I have seen is about 10AWG. I guess you can, but I'm sure it ain't cheap, and cheap is my first name these days.

The 1AWG is 7 conductor Cu. I can just use a tinned lug, right? My inclination is to solder it as well, what do y'all think of that?

Such fun stuff. Can't wait to start living there now!

Jonathan

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[bob g]

you might look into getting a "hammer" crimping tool and some eyelets to fit your

cable size.

hammer crimps work very well and generally don't need soldering provided you seal them up with shrink tube to keep the water out.

good score on the cable

what are you going to use for conduit?

if it were me i would consider coil black plastic tubing,such as used for water lines, its pretty tough and waterproof and will require no joints underground.

bob g

[hiker]

try some garden hose--cheap-cheap........

should last for years buried underground..

[frackers]

Irrigation pipe - I've just run 80m of 240volt cable up a 16mm pipe ready for burial. Its on the surface at present (ground still too dry for trenching) but it will go 3' under sometime over the winter. UV proof 'lateral' pipe (thin wall) is cheap (or it is here!!) but then the 3km of it I've installed so far means I buy in bulk :-)