I have a terrible setup. But first, let me say that I used a voltage meter to get a reading from my outlet, and it was starting at 119.5 volts right off the batt, with nothing plugged in.

I am running a lot of things off of two household outlets, most likely rated at 15 amps on one circuit:

  • My Mac Pro (2012)
  • Two monitors
  • A halogen desk lamp
  • A small pair of crappy speakers
  • 9 (nine) external hard drives, including a 4-bay RAID solution.

The last bit is what worries me. 8 of the hard drives are all daisy chained together, using FW800. I have a power strip with them on it plugged into my power strip in the wall (a fire hazard...). When everything above ^ was powered on and running, my line voltage dropped to 118.

To be specific, I am trying to copy large video files from these 8 drives, over to the RAID When the copy started, it stopped halfway through (24 hours later), and one of my drives had been "disconnected improperly" or "removed without being ejected." I tried starting the copy over and this time it failed even sooner, with all the drives ejected "improperly." It could be a software bug, but I suspect it was hardware/power related, e.g. drives are underpowered and are intermittently shutting off, or one of them has very corrupt data on it. But that is another issue entirely.

My main concern is: is 118 volts not a good sign when powering this many devices at home on one circuit?

Note: I am in the USA.

  • for starters, what country/region are you in? What is the nominal voltage in your area? Mar 15, 2014 at 8:45

2 Answers 2


Nearly all computer PSUs can run on (take as input) 100-127V/200-240V at 50/60Hz. 118V is in the normal range. Mine is higher at 123V. This is fine for a computer PSU but the external drives have smaller power adapters that are less tolerant than the PSU in the computer.

Perhaps you should get a UPS or at least a voltage regulator. Voltage regulators are commonly uses in locations with brown outs, where the voltage drops below 100V. And UPS are used in locations with black outs where the voltage drops completely.

If you think that there is a problem with the power service or the wiring, I suggest you contact your electrical service provider or consult an electrician. I am neither.


Most places have a mains power specification that includes a +/- 10% though in my region the spec is 230V with up to +10% or -6% giving the range to be from 213V to 253V.

If your power is nominally 120V then its acceptable range could be 108V - 132V. If it's also a 15A rated socket this would mean it's a 1800VA rated wall outlet.

Making generous guesses as to the maximum power consumption of those devices could give you

  • 800W - MAC
  • 100W - both monitors combined (assuming LED LCD)
  • 50W - Desk lamp
  • 100W - speakers
  • 306W - all 9 hdd (9 * (12*2 + 5*2))
  • 50W - NAS box processor

Total: 1406 Watts

Assuming a power factor of 0.8, this would mean you could be using about 1760VA (VA = Watts / power factor).

However its very likely that you aren't using all of your devices at their maximum power simultaneously. Graphics cards, all cpu cores, internal hdds, externals hdds etc.

Even though it does seem to fit in the rated power of the outlet, that is a lot of stuff in one outlet. Perhaps a power meter would be a good idea to see for sure how much power you are using. Also most houses are wired up with multiple outlets coming off the same cable that also has the same maximum limit as the quoted outlet maximum. An electrical contractor would be the best suited to tell you if you are overloading things or not.

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