Regarding the wiring, old 230/220v lines had no neutral. 2 hots and ground was it. Now code rules the day. Now all 230v setups have 4 wires -- 2 hots, neutral, and ground. 120v has 3 now -- hot, neutral, & ground. Old 120v ones could have left the ground out, having only hot & neutral.
My old tank I pictured in another thread held 6 gallons (first pic below). I estimate my new one to hold 3x that since it runs for 3x longer than the old one ... so 18, when it says it's a 40-something gallon capacity. I agree with Whistlenut - that's my reason for suffering through a wide pressure spread, and increasing the tank size.