i have some antminer s3
but i only have 3000W to mining
i need to have max efficiency
3000w/120volts=25amps
keep in mind that as you volts drop you watts go down and amps go up
curently at my house i get 117 volts. a good idea would be to put a volt meter on your plug to see what you volts are at different times of the day and different days.
117v * 25 amps = 2925 watts
115v * 25 amps = 2875 watts
do you have a 25 amp beaker. that seams odd. residential is usealy 15 or 20???
Sounds like they are from Europe (Portugal?) where the voltage is 240V, so that would be only 12 Amps.