Wire gauge question

[spiked]

Hello,

Just heading up to camp to install a 225 watt poly panel which I will be running to a 20a MPPT. I have a 40 foot run from panel to MPPT. Question is that I have 60 feet of Romex NMD90 14/2 household wire with a 300 watt rating at the camp. Can I use this to run from the panel to MPPT?

Couldn't get a definitive answer in the threads...........

Thanks again

[sensij]

No, NM cable is not suitable for use in a PV circuit, or outdoors.

[Sunking]

No you cannot use NM-B cable, well by code anyway. But a camp site is not under anyones jurisdiction and no one gives a crap if you burn it down or hurt yourself. At 40 foot I seriously doubt the wire is large enough. At 40 feet you will need 10 AWG copper.

[foo1bar]

No you cannot use NM-B cable, well by code anyway. But a camp site is not under anyones jurisdiction and no one gives a crap if you burn it down or hurt yourself. At 40 foot I seriously doubt the wire is large enough. At 40 feet you will need 10 AWG copper.

A spec I found for a 250W poly panel are 30V and 8.3A at MPP

8.3A would be a 2.1V drop for 40' of 14 AWG.
So instead of getting 250W, you'd get 230W to the inverter.
Certainly not ideal - but if there's enough hours of sunshine (and/or a small enough battery being charged/low enough use) I think it'd still function.

That said, as has been pointed out, NM cable isn't intended for outdoor use. And I wouldn't want to have to explain that setup if my campfire got out of it's ring & a fire crew had to come put out the fire.

[Sunking]

The issue with NM (non metalic sheath) is it is not rated for sunlight, or moist/damp/wet conditions which is exactly what you have at a camp site. After a couple of months of sunlight, th ecable insulation will crack and peel off the conductors and expose the conductors. First gust of wind or rain would cause a electrical short circuit setting you up for a fire.

[inetdog]

I think that some people, not active in the field, include UF and other specific types under the general category of "non metallic", not restricting that term to NM. It is true that UF does not have any metallic sheath either.

[foo1bar]

The issue with NM (non metalic sheath) is it is not rated for sunlight, or moist/damp/wet conditions which is exactly what you have at a camp site. After a couple of months of sunlight, th ecable insulation will crack and peel off the conductors and expose the conductors. First gust of wind or rain would cause a electrical short circuit setting you up for a fire.

I think it'd take more than a couple months of sunlight in the woods. (and I'm assuming in the woods - because otherwise, you wouldn't need 40')
It'd have to degrade both the inner and outer layers of plastic to the point where wire is exposed.
And the wires are physically separated by the bare wire - so it'd have to have each side short to the middle - or something that bridges between them across that ~1/8" space.
And I'm assuming that the camp is a short term thing (ie. 1-2 weeks for hunting or something) - so I'd would be more worried about the campfires. Those are very common ignition points for uncontrolled fires.

[Sunking]

I think it'd take more than a couple months of sunlight in the woods.

It is a camp site under no authority. I could care less what they do.

If it were me and it is not, I would use Triplex service wire which is made to do exactly what he want with messenger to support itself. But heck what do I know or care.

[Mike90250]

And the wires are physically separated by the bare wire - so it'd have to have each side short to the middle - or something that bridges between them across that ~1/8" space.

Woods, to city folk, is a quaint park where you see squirrels. But when you live there, every critter wants to chew and test every strange thing. Poly pipe, neoprene line with ozone, every elect cable not in metal conduit. And tree branches falling all the time on stuff.
I would not count on the bare ground wire helping the situation at all.

[inetdog]

When they first built the Bay Area Rapid Transit system (BART), they used a type of cable for their block signalling whose plastic sheath was incredibly tasty to gophers. The entire wiring system had to be replaced.
In the same time period they realized that their beyond-state-of-the-art block control system included what became known as the automatic train replacement algorithm.
When a train stopped for any reason there was a good chance that rust spots on the wheels and tracks would cause an open circuit on the 5VDC detection system that was clearly far superior to the old 24/48V stuff. When the train suddenly disappeared the control system cleared the next train to enter the now "empty" block of track.

The initial fix was to have the stationmasters call the stations on either side each time a train left so that they could clear the next train onto that section of track. Later they automated it to have the display sign computers do the phone calls.
Those were the good old days.