Newer homes built in the US are more efficient and don't require amperage like the in the past. That's why you see 100 AMP service for a normal size 3 bedroom 2 bath house now. My house was built in the year 2000, which is considered new in the housing world and came with 100amp service. If the house was 20 years old, I bet it would have 200-300 amp panel in the basement.
FWIW I have
never seen a 300A panel in a home. 200A is the highest I've come across and that's usually in McMansions. Standard is 100A, and I've seen much, much older homes at 60A.
2000 watts(approxomate Neptune draw) / 110v = 18 amps per Neptune. (USA)
5 Neptunes would Max-out 100 amp service right there
100 amp service means 100 amps at 240v, so that would give 200 amps at 110v.
I have 200 amp service and don't even have 220, I installed it myself under the direction of professional Electrical contractors, and the county inspector. I believe him.
Volts x amps = watts, Period. You can re-arrange that any way you like.
Watts / amps = Volts
Watts / Volts = amps
But if you really want to save $ on electric, you MUST get a Power factor correction Capacitor
it will save you 20-25% off the top if you are seriously mining
(The scam is electric companies actually charge by the volt-amp, and not by Kilowatt-hours) This corrects that.
http://www.eaton.com/Eaton/ProductsServices/Electrical/ProductsandServices/PowerQualityandMonitoring/PowerFactorCorrection/index.htm