A couple years back when lots of us were beating this wire thing up in a fairly serious fashion on BNO, I decided to do a test just for grins.
I made a jig that held a piece of wire and wiggled it... granted quite a lot... and then I counted how many wiggles it took to kill various types of wire.
It was a completely non-scientific test compared to how scientific one could probably get, but it illustrated the main point, that regardless if solid wire will work, it sucks as a choice for RV's when more robust wire types are readily available.
Here's a copy of the post: (Note, fast Fred sent me some boat wire to test and it arrived after I'd done it. I tested it later on and it performed about as well as the UL1015 wire I tried) Anyway:
Masochist that I am, I went down to my machine shop this morning, and set my milling machine up with a 1.5" stroke on the quill.
I then took a piece of #14 THHN solid wire, chucked it up in a drill chuck and the mill vice, and by moving the the quill handle up and down repeatedly, started bending the wire by an exact amount, over and over to see how many bends it took to fail the wire.
IT TOOK 11 BENDS on the SOLID THHN and it broke. I tried it again, and the second time, 11. Quite consistant!!
Then I put an ever-so tiny nick in the middle of a third piece, to simulate a sloppy strip job, and tried again.
This time it failed in 7 bends, not surprisingly right at the nick.
NEXT, 14 ga STRANDED THHN (14 strands)
This wire took only 12 bends and the first strand failed. At 60 bends, more than half had falied, and the whole thing broke at 98 bends.
OK, now for some UL1015 stranded (42 strands)
Two strands failed at 110 bends.
By 300 bends there a total of four failures
Total failure finally occured at 460 bends
FINALLY, Contractors cord:
For my last test, I found the CHEAPEST 14 ga contractors cord I could lay my hands on (like a $9.99/100' special at Home depot, that is now 10 years old and well used), and it had 28 strands. I stuck it in the gauntlet, and by 500 bends, not one strand had broken yet. I gave up. I also got so "in to it" that I forgot to take photos of it.
My arm is very sore now, thank you.
Here's the photo so you can see for yourself:http://www.heartmagic.com/00WIREstory.JPG
So here are my conclusions, no longer an "opinion"...
(1) IF you tie everything down and there are absolutely NO vibration or resonant points at ANY of your wiring terminations, you can probably use THHN wire of either type and get away with it. But "getting away with it" is exactly what you'll be doing...
(2) In an indentical installation, solid THHN will fail a lot earlier than stranded THHN.
(3) ANY USE of THHN will fail a LOT earlier than an installation that uses good quality stranded wire.
(4) The "Contractor's cord arguement" can now be reduced to "quality of insulation", and I won't go there....
(5) I'm glad I used UL 1015 wire in my bus
(6) It will all fail eventually....