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#2 AWG or #4 AWG for a 170 Foot Run

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garybryan33

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The EG4 18kv will live In the carport, 170 feet away from the critical loads panel it will feed. The subpanel will have a 70-amp (80-amp if possible) main breaker. Do I need #2AWG or would #4 AWG for the approx 170tf run? A bit confused on whether the max voltage drop of 3% is for continuous only.
 

Voltage Drop Calculator | Southwire

www.southwire.com www.southwire.com
according to the calculator, there is a 3.6% voltage drop for 70A continuous using #2AWG
You will need to run 4 conductors: L1, L2, N, Ground

EDIT: Double check the calculator numbers, seems high.

That’s a pretty long run, you might consider using URD direct burial aluminum 1/0 quadruplex, might be cheaper.
Like this: https://www.wireandcableyourway.com...dame-underground-secondary-distribution-cable
This won’t fit in the 18kPV, you’ll have to transition to something smaller.
 
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You know, the real money sometimes is in the trench and hassle. i'd run 1/0 or 2/0 copper in 2" conduit, THHN red black white and green #6. That will put you at 150-200A for your AC feed. I'd snatch a piece of fiber optic cable down along with. $4-5K good forever. When the new gear comes out, and you decide to expand your power plant, you ain't diggin up the yard again. YMMV.
 
You can invest some of the savings in going to Aluminum and put it into bigger conductor.

FWIW our underground runs to POCO here are always done in aluminum, not copper. (Copper not allowed).
 
>> Does the ground have to be of the same size?

ricardocello said:
according to NEC 250.112, it can be as small as 8 AWG copper
Click to expand...

Is there a similar rule for the minimum size of the Ground wire for a PV Strings?

- I have a 150 ft PV String (150 V DC - 30 A) and plan to use #6 AWG (13.3 mm^2)

- For the ground, I have plenty of #12 AWG (3.31) , so I was thinking to use two #12 AWG in parallel (6.62 mm^2)

Note: #9 AWG is (6.63 mm^2) and #10 AWG (5.26 mm^2)

So should the Ground wire be #8 AWG (8.37 mm^2) ?
 
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zanydroid said:
You can invest some of the savings in going to Aluminum and put it into bigger conductor.

FWIW our underground runs to POCO here are always done in aluminum, not copper. (Copper not allowed).
Click to expand...
Interesting, but I'm not sure why copper would not be allowed in conduit. Perhaps aluminum holds up better in a direct burial scenario. I've just seen too many issues with aluminum in older homes I have owned. I think the newer aluminium alloys might be better, and the connectors are probably better/more elastic, but I just get this bad metallic taste in my mouth when I'm around aluminum wiring. Like drinking beer out of a can. ;-) I think the bigger it gets the less problematic it is, I have no basis for that other than I've never had a feed cable problem, and they always seem to be aluminum.
 
ksmithaz1 said:
Perhaps aluminum holds up better in a direct burial scenario
Click to expand...
Utilities typically use aluminum URD triplex for direct burial underground lines, like the one from my utility transformer (on the ground in a big ugly green box), to the meter base. It’s relatively inexpensive. I chose to use it for my 220 ft PV run because at the time it was like half the cost of doing copper THWN2 through conduit. You still have to terminate into an approved terminal block with anti-oxidizer.

I prefer my beer in glass bottles.
 
So did you put in a transition box on either end and roll back to copper, or just go straight in on both sides?
 
This stuff is stunningly inexpensive. So they have this stuff with smaller neutral 4,4,2/0, which should be fine, but no ground. I've got to run about 75', so now I'm thinking running this in a trench with much smaller conduit. I'm only looking for 150A, but WTF. My only question would be around a smaller Neutral. Put a 3" sacrificial stub as you bring it up from underground, I could get under $800 with all the connectors and everything.
 
ScrotusGobbleBottom said:
Wouldnt that be bad with dissimilar metals?
Click to expand...
The "Ideal industries" makes purple wire nuts to even connect copper / aluminum together so I guess it isn't as crazy as it's made out to be as they can just twist together.
the wire nuts can't be used for aluminum to aluminum though lol
There's some other brand that has a 3 terminal purple box for that..
none are big enough for the wire discussed in this thread though
both are NEC compliant
 
gotbeans said:
The "Ideal industries" makes purple wire nuts to even connect copper / aluminum together so I guess it isn't as crazy as it's made out to be as they can just twist together.
the wire nuts can't be used for aluminum to aluminum though lol
There's some other brand that has a 3 terminal purple box for that..
none are big enough for the wire discussed in this thread though
both are NEC compliant
Click to expand...
Thanks for the info!
 
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