APC Smart-UPS XL 3000


I have two of these APC units. They use NEMA L5-30P electrical plugs.

I'm using Kill A Watt EZ devices to measure the Amps used by my servers and other equipment with normal electrical plugs but I can't plug the APC units NEMA L5-30P electrical plugs into the Kill A Watt devices.

Does anyone have a ballpark idea of how many Amps an APC unit like this uses by itself without anything plugged into it?

  • At what voltage? – John Gardeniers Jul 8 '11 at 9:23
  • @John - From Wikipedia: NEMA L5 connectors are a series of locking connectors with a maximum specified voltage of 125 V. Supply connections are intended to be single-pole hot-neutral-ground circuits with a nominal voltage of 120 V RMS. – Mark Booth Jul 8 '11 at 10:49
  • @Mark, the plug rating is not necessarily the same as the supply voltage, which is relevant when current figures are quoted. I have no way of knowing what the local supply voltage is in some undefined location, so cannot determine what the nominal idle current for the UPS would be in such a case. – John Gardeniers Jul 8 '11 at 20:04
  • @John @Mark 120V – caleban Jul 8 '11 at 20:33
  • @John - Alternatively, you could have just looked at the web page caleban linked to! – Mark Booth Jul 8 '11 at 22:27

Looking at the spec, it suggests an Online Thermal Dissipation of 375.00 BTU/hr, which is apparently around 110W. Since any difference in current in and current out must be lost as heat, this should be a good indicator of the current draw of the UPS on it's own:

  • 110W at 120V gives us a ballpark figure of just under an amp.

If you want a more accurate measure, then I can think of two possibilities that might help.

  • The first option is a clamp current meter, which would allow you to measure the current through the UPS power lead. Subtract the power use of devices plugged into the UPS from this meters power usage and you will have your answer.

Note that just measuring the current draw of the UPS without load may not give you a very accurate indication of it's current draw under real usage. There will probably be a non linear relationship between power in and power out as total power use changes. It may, for instance, be more efficient in the middle of it's range, getting less efficient at very high or very low power usage. Ideally you should test under both normal and worst case load conditions.

  • The second, possibly cheaper option, is only appropriate if you are comfortable with (and possibly in some jurisdictions qualified to) wiring up your own mains power leads.

Buy a pair of NEMA L5-30P plug & sockets, plus a socket and plug appropriate for your Kill A Watt EZ device, then make a pair of leads, NEMA plug > normal socket & normal plug > NEMA socket. You can then plug your device in-between. Do be careful about wiring up your live/neutral/earth leads to the correct pins though. Ideally, if you aren't a qualified electrical, you should get one to do this for you.


We have 2 of these exact units and they are wired to 30 amp circuits. So anywhere from 20 - 30 I would say. We also have a 5000 watt Powerware unit that uses 30 amps.

  • 3
    But these APC units alone don't use 20 or 30 amps all by themselves do they? They'd only use that many amps after you plug servers into them right? One reason I say this is because if the APC units alone use 30 amps there's no amps left over on the circuit for any servers to be plugged in etc. I could be wrong. Based on the information on the APC website and googling around I don't have a good idea of how many amps they use alone all by themselves with nothing else plugged into them. – caleban Jul 8 '11 at 7:55
  • No, but after a power failure they also reload ;) This means they draw a LOT more than they give out while reloading. Line capacity must be able to handle that. – TomTom Jul 8 '11 at 11:10

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