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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!
 
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...

It does seem nutty that Al to Al isn't allowed.

I don't think Cu to Al is a good connection with pressure. Crimp terminals are listed, I figure break the oxide.
What this screw terminal could be doing is cutting through oxide and the screw carries current around from aluminum to copper wire. Still can't see why Al to Al would not be OK.

Twister® Al/Cu Wire Connector, Model 65, Purple

The Twister® Al/Cu Wire Connector is specifically designed to provide a secure connection while preventing aluminum corrosion. Pre-filled antioxidant compound prevents oxidation of aluminum conductors.
www.idealind.com www.idealind.com
 
Hedges said:
It does seem nutty that Al to Al isn't allowed.

I don't think Cu to Al is a good connection with pressure. Crimp terminals are listed, I figure break the oxide.
What this screw terminal could be doing is cutting through oxide and the screw carries current around from aluminum to copper wire. Still can't see why Al to Al would not be OK.

Twister® Al/Cu Wire Connector, Model 65, Purple

The Twister® Al/Cu Wire Connector is specifically designed to provide a secure connection while preventing aluminum corrosion. Pre-filled antioxidant compound prevents oxidation of aluminum conductors.
www.idealind.com www.idealind.com
Click to expand...
yea no idea why it isn't ok for al/al

People don't recommend those wirenuts anyway for copper/alum especially for long term even though NEC does.
If you run high amps (like more than 10...) in it the aluminum heats up way more than the copper and causes issues from posts I saw.

Those twisted ones have some paste in them to stop corrosion, doesn't seem that great

the wago style or these things (pic) seem better..
1712027902053.png
 
ksmithaz1 said:
Interesting, but I'm not sure why copper would not be allowed in conduit.
Click to expand...
Their side of the system their rules 😂

More seriously, I looked into it bc I wanted to pull copper through my existing conduit to get an ampacity bump. I think aluminum is actually easier to pull for the same ampacity as copper. Also it is way cheaper.

My aluminum #1 feeder has (presumably) lasted since 1980 at this house.
 
Hedges said:
It does seem nutty that Al to Al isn't allowed.
Click to expand...
I don’t think there are any twist connectors for bare aluminum. Maybe something to do with thermal expansion too? Superstition from all the old Aluminum branch circuit wires?

Not sure why you would need to use them though, I think there’s very little smaller ampacity Al that is not CCA (I’m assuming CCA has actually seen some adoption since approval), and usually it is small branch circuits where you would use twist connectors.
 
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