I’m planning on using 25’ of #8ga wire to attach my remote , 120w/12v solar panel to my solar controller which is located at my battery box.

aluminum wire is lighter and less expensive. Any disadvantage to aluminum over copper? Any loss difference?

Aluminum has very good conductivity but less conductivity. You will find voltage loss charts for both copper and aluminum. Copper loses less voltage. It may not matter for you, but just look at the numbers and be aware. Also when you join aluminum and copper wires together it causes a chemical reaction and deterioration over time so use ox guard or similar product on any union.

More care must be taken to install aluminum wire to avoid fire hazards. Intermittent heating and cooling from conduction cycles can cause connections to become loose with aluminum wire and possibly spark. Larger gauge aluminum wires are required to conduct the same loads as copper - so if space is a concern when routing, copper wins. 

Rob

  rb, good question, here's my take:  I'm old enough to remember all the horror stories and fires caused by the improper or non maintained use of aluminum conductors way back in the day even though that was typically higher voltage and higher current residential applications. During my years as a power distribution engineer typically one place I saw it specified might have been from the Utility transformer to the service entrance (where properly installed by trained utility company professionals) but NEVER inside a home thereafter.

 Some of the reasons it was less favored by myself and other professionals was:

  It can be more brittle,,,,,,,,,, Typically less flexible,,,,,,,,,,,,Typically doesn't withstand frequent bending as well as fine copper,,,,,,,,,,,,,,,,Requires the use of anti oxidant in certain connectors,,,,,,,,,,,Some connectors are NOT approved for aluminum,,,,,,,May require more connection maintenance,,,,,,Being higher in resistance requires larger wire gauge for the same current,,,,,,,,,,,Doesn't mate well with dis similar metal such as copper (battery action and corrosion potential).

NOTE I'm NOT saying aluminum doesn't "work" and for sure its lighter, IM ONLY SAYING BASED ON MY TRAINING AND EXPERIENCE I WOULD NEVERRRRRRRRRRRRRRR use it in an RV application (even if any codes allowed it Yeah Right lol). I prefer fine stranded copper conductors as they are more flexible and can withstand RV road vibration and even Marine Grade if one chooses. However for the "good side"

PS in your earlier post where 8 Gauge wire was discussed, I was thinking Copper. If you were to use aluminum and 8 Gauge in copper was actually necessary ??? that would have to be increased BUT I STILL DONT LIKE IT for all the reasons cited above. FWIW USE FINE STRANDED COPPER IS MY ADVICE. On the "good side" however if the RV has an external plug and you're ONLY using aluminum for the exterior run from panel to the plug, its not near as hazardous or unsafe or as critical as all that I described above and sure would  "work" YOUR MONEY YOUR RV YOUR CHOICE      

Best wishes

John T  Long retired n rusty EE but still believe this to be true. Consult trained professionals where fire or life safety is an issue.

Edited October 26 by oldjohnt

Poor way to save 3 cents. 

Thanks, I ordered 25’of pure copper welding wire #8.

but for my own edification.....how about copper coated aluminum stranded wire?

Still prone to the same faults as pure Al wiring, minus the corrosion. 

  On 10/26/2019 at 5:12 AM, rbertalotto said:

Thanks, I ordered 25’of pure copper welding wire #8.

but for my own edification.....how about copper coated aluminum stranded wire?

1) That 8 Gauge pure copper welding wire should work fine at the distance and current you're dealing with CONGRATULATIONS

2) I would prefer copper coated aluminum over aluminum only given the proper use and circumstances but it (aluminum core) can still have some (even if less) of the problems I spoke of above.

   John T  

  On 10/26/2019 at 5:12 AM, rbertalotto said:

Thanks, I ordered 25’of pure copper welding wire #8.

but for my own edification.....how about copper coated aluminum stranded wire?

I find best price on welding cable  is at welding supplies. Just pickuped some #4 today for .885 per foot

Bought 50' of Made in USA #8 welding wire (25' red and 25' black) at amazon for $42 with free shipping. Seemed like a reasonable price

That is high for #8. But you did n't have to leave home to get it though.

rb, Wise choice to buy Welding Cable (even if higher then regular) as its typically fine stranded and designed for high flexibility and vibration tolerant plus it has good quality tough insulation. You done good and yes a reasonable price !!!!!!!!!!!!!!!!!

 John T

I have found welding cable to have poorer quality insulation. I'm sure some are better than others. Marine grade seems to be consistently high quality, plus has tinned plated wire strands for corrosion protection. 50 feet of 8 awg is 42.50 with shipping at Genuine Dealz . com for a few $ more they will make to your length with proper crimped lugs. I would not use marine or welding cable exposed on roof.

  On 10/26/2019 at 5:12 AM, rbertalotto said:

Thanks, I ordered 25’of pure copper welding wire #8.

but for my own edification.....how about copper coated aluminum stranded wire?

Most welding cable is no UL listed.  Without a UL there's no way of knowing what the % of copper is.  The UL must be printed on the wire. 

The UL for welding cable is UL1276 ....FYI...UL1276 welding cable is not NEC approved for fixed of portable applications

Tinned coated marine wire is UL1426.

Wire for the solar installations is UL4730

 What can make matters worse and maybe even more confusing is I've owned RV's for 49 years and in many (not saying all) typical cases if you go to an RV dealer to buy wire and start throwing UL terms and ratings and questions to them unfortunately you may get the "Deer in the Headlights" look LOL. 

    If I was using wire that was all outside and ran from a portable solar panel to a plug on the side/exterior of an RV, at the very MINIMUM (in addition to more specs where applicable) Id want it rated for outdoor use with suitable ultraviolet protection, fine stranded copper with good vibration resistance and flexibility with a good insulation and jacket, and, of course, sufficient ampacity so as to limit line voltage drop. I'm not familiar with all the UL or any NEC or RVIA or any other ratings or codes required for wire strictly OUTSIDE an RV from a solar panel to an external plug ?????????? The Solar providers can probably answer that better than an RV dealer. I've purchased my Solar equipment from Solar rather then RV suppliers as they seem to be more knowledgeable in that regard.  For sure rooftop solar panel wiring exposed to so much sunlight must be high quality and rated for ultraviolet !!!!   Id say such use (Outside wire from solar panel to external RV plug) would be different from pure RV INTERIOR  or Marine applications.

 Do your research and homework and consult trained professionals when selecting components and wiring DUH

 John T 

Edited October 27 by oldjohnt