Electric water heater wire size question-solar water application

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Onokai

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I have a wiring size question -1st let me say I have a 80 gallon Rheem Solaraide tank that takes hot water directly (no heat coil fluid transfer )off two 4x8 solar water panels on roof. I set this up in 1981. This tank then feed my Rheem 40 gallon natural as water heater, The 1st rheem tank lasted 25 years. I replaced that tank in my preheat system in 2009.
Fast forward to today. I used finished last fall installing a 9600 watt ground based dollar electric array and am using a sol-arc converter. That said it has a function that when it has extra power it can feed max a say 3500 watt water heater element .My Rheem solaraide 80 gallon tank was never wired for electric (has ground wire only). Its an easy wiring job for sure.
I ordered the 3500 element thermostat gasket and plastic inner cover and metal holder bracket direct from Rheem.

The wire run is about 70-80 feet. I'm thinking #10/2 or 10/3 romex with a 30 amp breaker. I say #10/3 if I go in the future with a smarter water heater . It looks like maybe I'm on the line for 20 amp 1 beaker and 12/2- as well any thoughts -I tend to overkill.
Electric water heaters draw a load for sure-whats the censuses? #10 0r #12 wire size?

In this setup my cold season ,about 5 months I can preheat with free power then shut that down the electric part when the sun works better on roof water solar panels and fills that 80 with 170 degree water.
also what the thought of putting in a new anode at this time?
 

wwhitney

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But the NEC considers a storage type water heater of 120 gallons or less to be a continuous load (422.13). So a 3500W heater would require a 20 amp breaker and wiring with an ampacity of at least 18.2A.

Cheers, Wayne
 

phog

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Man, is the cost savings really worth going with the absolute minimum Romex? 12/2 is like $25 and 10/3 is like $55 for 50ft. Why wouldn't you just run the bigger stuff if there's any chance you'll want to do something different in the future? You can run a small appliance on 10ga no problem forever, even if you never need the bigger gauge wire; whereas re-running the entire circuit in a couple years merely to upsize from 12ga to 10ga (or to add the third conductor) could be a big pain in the butt. I guess if your run is 300ft the extra cost could add up, but it doesn't sound like that's the case. Just my $0.02
 

Onokai

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I'm going to run running 10/3 now for sure -buying a 250 foot roll so I'll have some extra for some future mini spilts going in in JUNE
 
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