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.