I have an APC BX1500M UPS rated at 900 W and 1500 VA.

I want to attach three devices for a combined wattage of 816 Watts and a combined amperage of 8.1 Amps.

*Note: This total was determined from the specs of the attached devices.*

Given that the UPS has Automatic Voltage Regulation, let's assume it always outputs 120 volts under normal fluctuation conditions, so that we do not need to be concerned about possible output voltage fluctuations.

The total load falls within the Watt Rating and VA Rating. However, if we divide the Watt Rating of 900 W by the assumed output voltage of 120 V this leads me to believe that the UPS is further limited to only be able to supply 7.5 Amps total output without detriment.

Therefore, I believe I cannot hook up all three devices without come kind of drawback.

If I were to connect the three devices:

How would the UPS internally deal with this issue of an 8.1 Amp load?

What consequent drawbacks or other effects would occur over the short, medium, and or long term upon the UPS, it's batteries, and the appliances attached to the UPS due to this load?

How would the results differ from the scenario where two of the three devices connected to the UPS for a total of 576 Max Watt draw and 4.8 Max Amp draw?

Is Max Amps (the 7.5 Amps) another requirement when planning UPS that was not mentioned in the tutorials on how to "size" a UPS?

**Edit:** My current understanding is that the Watt Rating represents the true power available, and so it represents a * robust* limit that I can use to determine the capacity of a UPS, due to input A/C phase shifting. I'm not aware of how the input VA could be relied on to supply all of its amps into the output power of a UPS, so my "safe assumption" is that the amps are limited to what the Watt Rating provides. If my assumptions are wrong, explanation would be most helpful.

**Update:**

I talked to someone at APC and they gave me a *lower* number than 7.5 Amps.

They mentioned the 80 - 90 % Utilization Rule and gave me a number that was 1 full amp lower than the calculated theoretical max amperage of the UPS -- they told me 6.51 Amps.

Given that they are representing the UPS brand, I'm inclined to take this as the authoritative answer from APC.

This number will give me a roughly 4 minute UPS runtime and will ensure that no device connected will ever attempt to draw more electricity than the UPS can push out, so all the equipment should last as long as possible!

I may consider a 3rd UPS ; we'll see what I can manage

Any good thoughts on this outcome are appreciated and may also count as an answer if they help explain the situation

`How would the UPS deal with this?`

It will, but probably not for long.