Solid Romex versus stranded wire for panel to MPPT run

[searat]

I am trying to work out my wiring for a small solar system for my camp.  I have (2) 94W, 24 v panels and a MPPT charge controller.  I intend to run a separate wire to each panel and then combine them back at the box.  Most documentation you read says use all stranded wire. I purposely got the 24v panels and the MPPT controller for line losses between the panels and the controller at about 40 ft.  My question is can I (or should I) use 10-2, exterior grade Romex to run to the box and then switch to stranded wire?  It sure is a lot easier (and cheaper) to get exterior Romex rather than stranded wire.

[ghurd]

I use 'outdoor' romex all the time. UF-B.

With the 2 panels wired 40 feet seperate back to the box, 10-2 for each panel is way more than is really needed.  12-2 UF-B would be plenty, a lot less expensive, and still allow for expansion later.  Outdoor strain relief romex connectors are available for 12-2 much easier than 10-2.

Wire sizing chart.

http://www.windsun.com/Hardware/Wire_Table.htm

two cents,

G-

[drdongle]

IMHO stranded is far easer to work with but Romex will do the job. Just use wire rated for out door/UV.

[Ungrounded Lightning Rod]

For carrying current in a non-flexing environment, solid and stranded of the same number are equivalent.  (That's the point of giving the stranded wires a guage number.)

There may be an issue with flexing if your panel tracks, and there may be an issue with how well the wire connects to the particular type of connector you find on the back of your panel, especially under thermal stress.

For the run I'd use whatever is cheaper and more convenient to run - probably outdoor/underground rated (U) Romex (which I'll assume IS the cheaper one for the rest of this post).

If there's an issue with the connection to the panel (because you're using solid and they're using barrier terminal strips) I'd put spade lugs on the end of the Romex.  Crimp-ons should be fine but solder them if you're feeling paranoid.

If the panel is tracking I'd run solid Romex to a weatherproof electrical box mounted near the pivot, join it to stranded there (using electrician's twist-on splices) for the run past the pivot to the panel, strain-relieve both properly where they enter the junction box, and fasten the rest of the stranded run to the panel so the flexing occurs only in the part where it's intended.  If non-tracking (even if it's adjusted manually a few times a year for the season) I'd run solid all the way.

[ghurd]

I have no luck getting crimp-ons to stay on solid 12ga. so they all get soldered.

And I have better results soldering the "Blue" 14-16ga crimp-ons to 12ga wire, than the "Yellow".

Wire is up in cost right now and 12-2 w/G UF-B is just under US$50 for 250' roll here.

G-

[PEdoubleNIZZLE]

As far as what wire to use, if it's outside, you must use UF, if it's inside, you can use UF or NM-B (a.k.a. Romex). If you want to use stranded wire, it must be THHN/THWN/THW (usually you can buy THHN wire that is rated for all 3... the W means wet, as in outside) and must be in a conduit/liquid tght flexible (for outside). As for the colors, the bare/green is the ground, all grounds should interconnect with the ground from the main service (correct me if im wrong please, I don;t have my code book handy). The white wire has to be neutral... that its, it must be connected to the grounding system at some point... positive or negative ground, it's up to you. The black is the hot. Also, you can use any color except green, white, or a wire with 3 white stripes as a hot. Also, keep in mind that:

#14 is rated 15 amps

#12 is rated 20 amps

#10 is rated 30 Amps

_For romex

#8 - 40 Amps

#6 - 55 Amps

__For THHN_

#8 - 55 amps

#6 - 75 amps?

[ghurd]

With UF-B, I use the black for negative,

white for positive and color it red with red heat shrink or red perm. marker.

G-