Dual UPS (A/B) – Uneven load and one UPS showing 0% at low load

[SuhasDasari]

Hi all,

I’m looking for clarification on expected load behavior in a dual UPS (A/B feed) setup for rack equipment.

We have a standard configuration with:

• Two APC UPS units (A-side and B-side)
• Dual‑PSU network devices connected across both PDUs

From our measurements:

• UPS A is showing load (~180VA / ~0.8A)
• UPS B is showing 0% load on the UPS display

However, when checking the PDUs connected to UPS B:

• We can clearly see load on at least one outlet (~0.3A / ~30W)
• So there is load present, just much lower than on UPS A

[Teken]

All APC devices are notoriously inaccurate for displaying low power loads. Depending upon specific hardware, firmware, and internal components.

The minimum required load is 30% of the rated system’s maximum. As such the real world figure is anywhere from a minimum of 100 watts ~ 300 watts for the system to properly display the power / current.

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[SuhasDasari]

Thanks, Teken. That explains what we're seeing. Appreciate the insight. 👍

[Teken]

If that feedback helped provide the answer please mark that reply as a solution to help the next person asking the same.

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