Wire size 2nd opinion and neutral / ground question

[Crispy]

The optimal location for my planned solar array is 220 ft from my service panel in my cellar. This will be an off grid system connected to a Reliance switch box connected to selected circuits in my breaker panel, allowing me to switch between my solar and the grid.

I plan to start with a Magnum 4448 120/240 single phase inverter. The max 30 minute peak on this inverter is 5000 watts, so each leg would max at around 21 amps. Continuous rating would be 18.3 amps per leg.

I used an online voltage drop calculator and came up with 6 AWG wire size. It only gave the option to enter 1/2 the wire run length. I entered the full 220 feet. Using that parameter, I got the following results when combined with these additional parameters. The higher amp values were for the purpose of determining if I would have room for additional capacity to be added in the future. I wasn't quite sure which voltage / phase parameter to select, but the results were basically the same. I would assume the current flow through each individual conductor would be the main issue, but I could be wrong?

120V single phase @ 21 Amp = 4.4 volt drop to 115.5V
120V single phase @ 40 Amp = 8.4 volt drop to 111.6V                                                                                                                           240 single phase @ 21 Amp and @ 40 amp gave the same respective voltage drops as above.

I welcome any comments on these results. I am fairly confidant I should be ok here, but am not sure if the 1/2 wire run parameter is compensated for by the calculator based on the selection of AC or DC voltage, so I entered the full 220 feet since it will be AC.

Also if I up my capacity to the 40 amps, will I be ok with the resulting 111.6V per leg as far as devices that may be sensitive to lower voltages? My house wiring is all 12GA, so additional drop between breaker panel and load should be minimal.

Lastly, I am going to use THNN cable buried in conduit. Am I correct in thinking I will not need to run an earth ground, just my 2 hots and a neutral? Can I get away with a smaller diameter neutral or does it also need to be 6AWG? I saw a price of $.60/ft for this size wire, so if I can keep the cost down with a smaller neutral and stay within code that would be good.

Thanks,

Crispy

[birdhouse]

i'm not sure of the calculator you used, but many times, the reason they call it half the distance, is because the total distance is there and back...  thus half of that is the actual run length.  i like this calculator because it is very straight forward, and has plenty of options:

http://www.nooutage.com/vdrop.htm

i'd shoot for less than a 2% voltage drop as it's code, and will probably pay back in the long term.  as for wire, shop for 500' rolls.  even the big box stores have good pricing on these.  many times even buying 200' by the foot is more expensive than buying a 500' roll. 

as for the ground neutral thing, i'll leave that for others as i don't want to steer you in the wrong direction. 

adam

[Crispy]

Thanks for the link Adam. The results were within a few tenths of a percent of the one I used, but with the added parameters may be more accurate.

I saw the 2% rule in the notes. That is for DC. They recommend under 5% for AC, so if I want room to grow I'll probably need to go to 4AWG. Unless I can find a better deal that's $660 worth of wire at $.96 per foot.......ugh 

Crispy

[fabricator]

The people who bring you the grid use tens of thousands of miles of aluminum wire all over the planet. The alumnum wire from the transformer to my service panel is almost 1/4 mile long.

[birdhouse]

have you/are you using high voltage mppt?  that can make a huge difference!  i think morningstar tops at 150VDC while midnite solar caps at 200+ battery voltage in hyper VOC mode (i think, verify to be sure). 

even 50 volts excess in transmission could make a huge difference in wire size.  as fab states, i wouldn't automatically nix off ALU wire.  just make sure to put anti-ox on the ends, and retorque the connections after 6 months or so.  some old school electricians ive worked with put a tight loop in the wire just before the terminations to apparently give the wire some flex for expansion and contraction so it doesn't rip the lugs off a panel.  i doubt that would happen, but that's what the old schoolers say...

adam

[Crispy]

Fab,

That must be a hint  Aluminum instead of copper. Here's some 1/O 3 conductor that would give me a voltage drop of only 2.8% at 45 amps. Would this meet code if buried 18" in conduit? Looks like it can be buried without, but what depth is required for that?

http://www.wireandcabletogo.com/Aluminum-Building-Wire/Underground-Secondary-Distribution-Cable/1-0-1-0-2-Brenau-Aluminum-Building-Wire.html

I assume the one conductor with the yellow stripes is the neutral?

If this works it would cut the bill 1/3.

Thanks,  Crispy

[Crispy]

Adam,

I will be using MPPT with somewhere around 120VDC coming from the array, but the battery shed will be right next to the array. I'm calculating the AC line from the inverter in the battery shed to the house some 220 feet away so I didn't think my charge controller would be a factor for that, or am I missing something?

[fabricator]

Fab,

That must be a hint  Aluminum instead of copper. Here's some 1/O 3 conductor that would give me a voltage drop of only 2.8% at 45 amps. Would this meet code if buried 18" in conduit? Looks like it can be buried without, but what depth is required for that?

http://www.wireandcabletogo.com/Aluminum-Building-Wire/Underground-Secondary-Distribution-Cable/1-0-1-0-2-Brenau-Aluminum-Building-Wire.html

I assume the one conductor with the yellow stripes is the neutral?

If this works it would cut the bill 1/3.

Thanks,  Crispy

The smaller conductor will be the ground, I'm not sure about that wire but you can get direct burial aluminum wire, rent a trencher and you could run that trench 4' deep in about 35 minuites.

[birdhouse]

ahh, got it. 

i think code here for conduit encased wires is 18" underground.  honestly, if it were me, i'd put em in conduit, then run an extra 1" conduit (cheap) for cat5 or anything else that inevitably you'll want to get from A to B. 

adam

[fabricator]

That's what I did, right now I have one turbine, but while I had a trench I buried two 2" pvc conduit runs and two 1" conduit runs, so I have three empty conduits running out there right now with pull ropes in all of them.

[XeonPony]

The people who bring you the grid use tens of thousands of miles of aluminum wire all over the planet. The alumnum wire from the transformer to my service panel is almost 1/4 mile long.

you missed that on average the alu is carrying 25500 volts phase to phase, and then to the hous it is 240v w/ 6 guage for the average 200Amp service with a ground bonded neutral making the pannel see a 4 guage cumulitive neutral

if you really need to shave the cost down and push high amps a 240 to 600v transformer is really good for that, but 220f? that ain't bad, for efficiency and long term, I prefer to stay with copper even though it adds a bit.