wire/conduit size/cost sanity check...

[JimP]

I am designing as system with 36 panels in 9-panel 450V 9A strings. I'd like to run each string back to a solark 15k instead of combining them at the source. The problem is that my shop roof where I can put the panels is almost 300' from the house. The solark has to be at the house where the service entrance is so I can net meter.

Do I really need 3 10 gauge wires per string? 12 THHN wires * 300' * $.64/ft at Lowes = $2304 in home run wire? That's 14.4 cents/kW just for the wire!

Looks like either schedule 40 or 80 1" conduit will meet code. Not sure I want to pull 12 wires through 300' of it though. A bit of the path is under a gravel parking area - does that mean 80 is required? For the whole length or can I switch once in the yard? For the schedule 40 I am seeing 1.70/ft for 1", 2.50 for 1.25" and 2.80 for 1.5". That's crazy for plastic pipe. And another $500-850 :-(

Is it possible to splice a THHN wire and use it underground? 300' wires from 500' doesn't work out very efficiently, so I would probably have to buy them all as 300' at by the foot pricing.

Thanks,
Jim

 

[Hedges]

You should have a ground wire, so buy 1000' for positive, negative, ground. or 2500' for several runs.
Combining into one wire probably makes the most sense. Also avoids derating for conduit fill.
Whatever size conduit you think would work, go larger. Don't believe the fill tables. Just because you're allowed, doesn't mean you can.
Yeah, absurd prices. What rigid used to cost.

12 AWG Stranded Copper THHN THWN-2 Building Wire Lengths 500 Feet to 2500 Feet | eBay

Aluminum XHHW THHN. THHN applications are suitable for use in dry locations only at temperatures not to exceed 90°C. 12 AWG Stranded Copper THHN THWN-2 Building Wire. THHN THWN-2 TFN TFFN. CCW Armor 15kV.

www.ebay.com

 

[400bird]

Depending on where you are, you should only need a single #6 ground.
Then 2 wires per string. So eight #10 and one bare #6

My local electrical supply place has #10 THHN stranded for $0.36/foot. Comes out to more like $900 plus the ground, so maybe $1200

 

[JimP]

Thanks to both of you - much less shocking of a price. Hard to believe Lowes is double. I can check around locally and fall back on the ebay seller if necessary.

 

[labeeman]

Is it possible to splice a THHN wire and use it underground? 300' wires from 500' doesn't work out very efficiently, so I would probably have to buy them all as 300' at by the foot pricing.

NOPE

 

[Bkord]

Copper is so high right now. I ran 8 #8 wires for mine at 260’. Shooting for less than 1% voltage drop.

 

[Prince Of Darkness]

HD is $0.29/ ft in 500 ft spools -- search term:
' #10 AWG Stranded X 500 feet ' I am too stupid to shorten links ...

HD used to carry pull boxed THHN, 1000 ft per box, but do not see it there, now.

Electrical supply house may be your best bet, Good Luck, POD

 

[JimP]

Thanks all!

 

[rhino]

For the conduit there is also UL listed HDPE you can get on reels instead of trying to piece together a bunch of PVC pipe. I had ordered a couple reels from Chapman Electric and had it shipped freight. Is also much more environmentally friendly than the PVC pipe. It was 3000ft of 1 1/4 SCH40 with 1000lb pull tape already installed. Was $1784 without shipping and taxes from Indiana in 2019. I had no trouble pulling "Stephens" cable which is 2 2 4 gauge cable using the pull tape over 500ft. I did not have the pipe buried near the panels where the cable was going in when feeding it through the conduit to avoid the sharp turn there.

 

[rhino]

Also seeing the prices people have mentioned I ordered all my cabling for the panels from https://www.nassauelectrical.com. $0.43/ft for the 10AWG THHN/THWN-2 copper + shipping from Florida.

Edit: I missed that the eBay listing above was for Nassau ?