I recently powered up my 2 antminer S9 for mining bitcoin. Don't worry, this is all electricity questions.

So I have them running off a 240v single phase plug on a 30 amp breaker with wire gauge as follows: breaker to outlet 10awg; outlet to junction box 12awg; and junction box to individual plugs 12awg.

Now when I originally did the calculations for this I was going off the manufacture specs for power consumption which is 1330 watts each. meaning about 6.15 amps each. But after doing the install and everything,I stuck my clamp meter amp gauge on the wires. I'm getting 11.6A on one of the wires and 11.9A on the other. So if my math is correct this would mean that each one is drawing 2500 watts and that is WAYYYY outside of the amount of power this thins is rated to be able to produce. it is supposed to max out at 1600 watts.

The total length (from breaker to computer) is about 85ft total. I know there is a voltage drop of like 3-4 volts but that's fine... it's just confusing the hell out of me why I'm getting such high amperage readings. I have one more machine in the mail still, and had originally planned to run it on the same circuit, but now I'm concerned that I have to now make a new run for the entire thing to have all 3 on one breaker.

Also this just hit me: a 30 amp breaker means 24 amps is about the 80% max line. I'm drawing 11+- amps from each leg... so is that 22 amps on the entire circuit, or can I safely draw 24 amps on each leg of the circuit? Does anyone have any ideas how this is possible? Below is the spec sheet for the power supply from the manufacturer.

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  • Are you sure you're running these at 220 volts? If you run them on 110 volts, then measuring 11 amps with your ammeter would make sense. Measure the voltage with your multimeter just to be sure.
    – Dotes
    Dec 8, 2017 at 2:44
  • So I'm running a 240v circuit, each leg is 120v. And each leg has about 12amp draw.
    – rasmukri
    Dec 8, 2017 at 2:54
  • Show us a diagram of how you've wired it up. What you're describing doesn't add up.
    – brhans
    Dec 8, 2017 at 2:55
  • 3
    Ok so 1330w/240v=5.6amps, but you're not powering it with 240v. You're using 120v. 1330w/120v=11amps which is what you're measuring. You did the math with the wrong voltage.
    – Dotes
    Dec 8, 2017 at 2:59
  • @rasmukri because current flows in loops. You are expecting 12A, and there it is coming down the L1 wire... So if the L1 hot conductor is carrying 12A... then what? How is this 12A getting back to source? Neutral? L2? Earth? A family pet? Are any family pets yelping? Dec 8, 2017 at 7:15

1 Answer 1


First issue here is safety. With 12 AWG wire on circuit, circuit breaker should not be larger than 20A. This is code violation.

OK, where are you measuring the current? On the common wire going into panel? If you have x amps current leaving panel on one conductor on 240 VAC circuit, then must have same current going back to panel on other conductor. So 11.9A total current x 240V = 2856W. Divide that by 2 = 1428W. Sounds about right to me.

  • Ok so i have everything hooked up with the third miner and I'm running 18.2 amps on 12 awg wire. I'm working on getting a smaller breaker but I've seen things say 12 awg can handle 20 amps, so i will have 18 amps drawing 100%of the time so will that be safe? or since its constant and never stopping load do i need to go bigger to 10awg?
    – rasmukri
    Dec 8, 2017 at 18:48
  • 1
    If a circuit is loaded continuously (code says more than 3 hours at a time is continuous) , then it can only be loaded to 80% capacity, to 18.2A is too large a load for #12. Wiring should all be #10 with 30A breaker.
    – Paul S
    Dec 8, 2017 at 21:18

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