# Quick question size wire?



## budgetprepp-n (Apr 7, 2013)

Hi,
I'm gathering up everything I need to install second solar set up that I'm going to tie in with the working
set up that I have now,, But I do have a question this system will have a max of 470 watts 235 ea
For wire that goes from the panels to the controller do you think 12 awg will be OK

I'm going to wire the panels in parallel.


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## paraquack (Mar 1, 2013)

I assume the 35 is volts. So that would be 470 divide by 35 = 13.43 amps. 12 gauge wire (20 amps) should do fine if the length of the run is short. Personally I'd go with something larger, at least 10 Ga.


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## alterego (Jan 27, 2013)

I Am Surprised There Would Not Be A Chart Available For Reference. The Big Thing Would Be The Total Length Of The Run. I Am Not Sure That Would Show Up. It Is Always Best To Go Up A Size But Ten Gauge Is A Pain In The Add To Work With.


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## paraquack (Mar 1, 2013)

Use stranded, THHN. very easy to handle. I've used it for years. Pulls so easy thru conduit, it's a dream. Has a nylon outer jacket to make it soooo slick.

Low voltage is a pain "pushing" the power thru wire, too much voltage drop can really play havoc with a system. IMHO, anything close to 25 feet, I'd go 10 Ga. * According* to the chart at the website (page 8), for 48 VDC allowing a 3% voltage drop you'd be able to use 14 Ga. wire for a 19 foot long run. 10 Ga. lets you have a 24 foot run. Working with low voltage is a lot different than working with 120 VAC to 480 VAC. You need to really measure the length of the run. The wire size will really feak you out.

http://www.zetatalk.com/energy/tengy10s.pdf


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## alterego (Jan 27, 2013)

Thanks For The Chart Post parQuack Very Helpful.


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## Prepadoodle (May 28, 2013)

Power loss in watts is equal to the current squared times the resistance, or P=I^2R

Since the current (in amps) is squared, doubling the current means you will lose 4 times the power in any given conductor.

Conversely, if you cut the current in half, you will lose only 1/4 the power in that same wire.

Power (in watts) is equal to the current times the voltage, or P=IE. It's usually better to wire your panels in series, which will result in a higher voltage, lower current setup that will have less power losses in the wiring.


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## 1skrewsloose (Jun 3, 2013)

Most home improvement stores sell DIY guides for this stuff. Most likely they can walk you through step by step. Ditto on, whatever size they recommend, go heavier if you can. Better to be safe than sorry, and you may want to add on at a later time.


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## budgetprepp-n (Apr 7, 2013)

This is what I will be working with. Two of these I'm hopping that the 12 awg wire will be OK I have a 100 ft roll That I got trading
These will be in parallel 
The controller will only be about 25 feet away 


I was looking at some of the kits and they use the 12 awg on the 400 watt set ups 
I'll see if I can find a 500 watt set up and see what they use


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## HuntingHawk (Dec 16, 2012)

I recommend 8 gauge. Its 29V you will be working with, not 37.


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## Prepadoodle (May 28, 2013)

Putting 2 of these in parallel, you will get a rated max of roughly 29 volts and 18 amps. The theoretical power would thus be 522 watts, but since there are internal losses, the rated wattage is 470 watts for the pair.

12 gauge wire is about .159 ohms per 100', so your line loss would be 18 * 18 * .159 = 51.5 watts per 100" of wire, which is about a 10% loss.

8 gauge wire is about .065 ohms per 100', so your line loss would be 18 * 18 * .065 = 21.0 watts per 100" of wire, which is about a 5% loss.

Running these in parallel, you get the same wattage, but would see 58 volts and 9 amps.

12 gauge wire is about .159 ohms per 100', so your line loss would be 9 * 9 * .159 = 12.9 watts per 100" of wire, which is less than 2.5% loss

Note that these calculations are based on a 100' run. Obviously, shorter runs would lose less power, and longer runs would lose more.


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## budgetprepp-n (Apr 7, 2013)

Prepadoodle said:


> Putting 2 of these in parallel, you will get a rated max of roughly 29 volts and 18 amps. The theoretical power would thus be 522 watts, but since there are internal losses, the rated wattage is 470 watts for the pair.
> 
> 12 gauge wire is about .159 ohms per 100', so your line loss would be 18 * 18 * .159 = 51.5 watts per 100" of wire, which is about a 10% loss.
> 
> ...


Ok do so these look like decent panels? And I only got to go about 25 - 30 feet to the controller. 
So at 50feet or less with 12 awg I might get a 5% loss? What size controller would you get for just these two panels?


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## PaulS (Mar 11, 2013)

budgetprepp-n said:


> Ok do so these look like decent panels? And I only got to go about 25 - 30 feet to the controller.
> So at 50feet or less with 12 awg I might get a 5% loss? What size controller would you get for just these two panels?


The standard is 3% loss - in the industrial truck industry it is under .5 volt drop! you would need a lot bigger wire to meet that spec. 
The 3% loss does not just vanish - it turns to heat and too much heat will destroy your wiring and components.
I second the advice to always go to the next bigger wire (lower gauge number).


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## budgetprepp-n (Apr 7, 2013)

PaulS said:


> The standard is 3% loss - in the industrial truck industry it is under .5 volt drop! you would need a lot bigger wire to meet that spec.
> The 3% loss does not just vanish - it turns to heat and too much heat will destroy your wiring and components.
> I second the advice to always go to the next bigger wire (lower gauge number).


Ok in redneckanez are you saying that using the 12awg wire is way to small I might burn something up? 
And do these look like good panels? PaulS you really need to get out more


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## PaulS (Mar 11, 2013)

I was out in the sun for over seven hours! I don't need to get out more I just need to stop volunteering to help!

I would say the smallest wire I would use would be 10 gauge and if the amp draw was more than 30 I would opt for 8.


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## Prepadoodle (May 28, 2013)

budgetprepp-n said:


> Ok do so these look like decent panels?


Sure.



budgetprepp-n said:


> So at 50feet or less with 12 awg I might get a 5% loss?


Correct. Keep in mind that the 5% is at max output. Your average loss will be less since, on average, you will be handling less than max amperage.



budgetprepp-n said:


> What size controller would you get for just these two panels?


For a small system, I would always opt for a MPPT type controller, which will squeeze max performance from the system. I would wire them in series and use a controller such as the Morningstar SunSaver 15 Amp MPPT Solar Charge Controller. ($225)

The MPPT controller will handle a wide range of input voltages and convert whatever it gets into what your 12 or 24 volt batteries require.

If you insist on wiring them in parallel, you will double your current and need at least a 20 amp controller (30 would be better). If that's what you wanna do, I would go with the Morningstar TriStar 30 amp MPPT Solar Charge Controller. ($355) Note that this controller would allow you to add 1 more panel at some point in the future.


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## Prepadoodle (May 28, 2013)

Run the panels in series and you will see less than 1.5% loss over your 50 foot run and only be dealing with 9 amps, which your #12 wire can handle. You save money on wire and on the controller.

By the way, 12 gauge wire is rated at 9.3 amps in a power transmission application. 10 gauge is rated for 15 amps, and 8 gauge is rated at 24 amps. (American Wire Gauge Table)

This means that #10 wire is undersized if you insist on running your panels in parallel. Have I mentioned that I would run them in series? LOL


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## budgetprepp-n (Apr 7, 2013)

Prepadoodle said:


> Sure.
> 
> Correct. Keep in mind that the 5% is at max output. Your average loss will be less since, on average, you will be handling less than max amperage.
> 
> ...


 OK,, this might sound a little nuts but I pick up a little shade certain times of the year. I was messing around with the 3 panels experimenting. 
When they were wired in series it seemed like when I got a little shade on just one of them it pulled down the power from all of them.
This happens a lot in the early fall.

But when I wired them in parallel I didn't get as much power but the shade didn't seem to affect it so much.

And yes I'm going to use a 30amp MMPT like the one I'm using now on the excising system. 
Lower cost unit but it seems to work well

The controller I'm using is like the one on the right. 30A


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## Prepadoodle (May 28, 2013)

If you are running them in parallel, you will need AWG 8 wire because your system will put out a max of 18 amps.

For a 50' run of #8 wire, your losses would be: 18 * 18 * .031 = 10 watts, which is roughly 2.1%


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## 1skrewsloose (Jun 3, 2013)

Interesting this came up, I work maintenance in a 50 yr. old manufacturing facility. #12 is all over the place running 30 amps, now code calls for #10. We always know when we run into old wire cause its solid, not stranded, and a sob to pull through conduit to replace. I keep a reference book "ugly's" to get close, but they change the regs so often it doesn't pay to try to keep tabs on them, we farm a lot of work out, liability concerns.


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## BullseyePrecision (Jun 10, 2014)

Code is 10 but 12 would work


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## 1skrewsloose (Jun 3, 2013)

BullseyePrecision said:


> Code is 10 but 12 would work


So true, for all those years no problems, go figure


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## budgetprepp-n (Apr 7, 2013)

My #12 is fine wires is this good or bad?


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## 1skrewsloose (Jun 3, 2013)

Myself, I wouldn't loose any sleep over it, use breakers or fuses and you'll be good to go. my .02. Not looking to help you burn your house down. Might have misread your post, you mean "fine wires" as in stranded ,a number of individual wires bound together? Yea, You're OK. don't even think they sell solid wire of that gauge anymore. Yes, you can still buy romex in 14 0r 16 solid, but i think thats about it.


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## PaulS (Mar 11, 2013)

I installed 10AWG 3+1 Romex in my shop - solid wire with three conductors and a ground. I know that 8AWG was available when I bought the 10AWG. 

I only used 14 AWG for my lighting circuits - 2 circuits of 3.2 Amps each - not much loss in those wires.
The outlets were wired with 12 AWG - 4 circuits with 5 outlets each and then 5 circuits with a single dedicated outlet for the larger tools.
I used 10 AWG 2+1 for my welder and compressor 240 volt at 20 amps.
The 10AWG 3+1 was a dedicated circuit for the heat pump. The run was 5 feet.

When I wired my car I used nothing smaller that 16 AWG - even though the manufacturer used wires down to 22 AWG. I use 00 AWG for battery cables and 4 AWG for the alternator output.

I know - I have been told that I "over engineer" everything, but I don't have failures either.


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