2 Replies Latest reply: Jan 15, 2010 9:27 AM by Chris Hylton
Chris Hylton Level 1 Level 1
I am in the US (120 VAC) and am wondering if anyone has more details concerning the amperage usage on these units. Apple tech specs show only a MAXIMUM of 12 amps when running in the Low range (120 VAC). I am assuming that the maximum of 12A is during startup draw and possibly under heavy load conditions. But, is there a "normal" draw?

The reason I am asking is that in the next 60 days, I will be replacing 18 PPC G5 units with the MP 8-Core units, and there will be a period of time that I will be required to run both units (due to software and workflow issues).

In most newer wiring scenarios, the breakers are rated for either 20 or 25 amps, and will trip at an 80% load.

I've got LCD's (minimal amp requirements), so I'm trying to determine how many units per circuit I can have running without tripping breakers.

Any advice would be greatly appreciated.



27" Intel Core 2 Duo 3.06 GHz iMac, Mac OS X (10.6.2)
  • W7AY Level 1 Level 1
    I have an 8-core (Nehalem) Mac Pro with 14 GB of RAM and two internal drives. The measurements cited here are observed on the information display of an APC Back-UPS XS 1500 that has an additional 20" Apple Cinema Display plugged into the (measured) backed-up outlets of the UPS.

    This Mac has a second display but it is not connected to the backed-up outlet of the UPS and therefore not measured, but there could be extra power draw by the GPU because of it.

    The measurements are taken with the line voltage at about 119 volts RMS.

    When booting, there is a large instantaneous in-rush that showed over 400 watts, but it is just for the blink of an eye, so I wouldn't trust what the XS-1500 tells me. The in-rush current is non-trivial, though. I had to change to the XS-1500 UPS because an RS-900 UPS that I had earlier used with a dual core G5 PowerMac, which this MacPro replaced, did not have enough capacity to allow this Mac Pro to boot.

    During booting, the peak power draw is about 205 watts. The XS-1500 may not see spikes in the power draw, so the actual peaks may be a bit higher than 205 watts.

    After booting and when idle (no active apps), the power draw is about 170 watts.

    When put to sleep, the Mac Pro and the display together runs about 14 watts.

    I have written a (antenna design) program that uses Grand Central Dispatch and it can push Activity Monitor past 800% (I have seen it go up to 1200% on this mere 8 core machine, so I am not sure how much you can trust Activity Monitor either). In that condition, the power draw is 270 watts.

    All in all, the Mac Pro is quite power efficient, but you may want to stagger the booting of your 18 machines just in case the in-rush is too great.

    That being said, there is an unresolved bug as of 10.6.2 (you can find it in a different Mac Pro thread here) that causes power consumption to bump up to 240 watts (on my machine) whenever Core Audio is actively running. This jump in power occurs even when you play music in iTunes and occurs even when I use a couple of external USB or FireWire Sound Cards that I have (including the Griffin RadioShark and an external USB speaker). A couple of apps that I have written uses Core Audio -- and I can tell that the jump in power happens the instant you start causing Core Audio to issue callbacks.

    Kok Chen
  • Chris Hylton Level 1 Level 1
    Thanks for the details on this... I had to remember how to convert from Watts to Amps. So from what you are saying, it seems that the draw can be anywhere from 0.1 - 3.3 Amps.

    I have 10 units arriving next week, so I can at least see how many I can get onto a single circuit.

    Thanks for your help.