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How to Choose an Industrial UPS

Sizing a UPS by load power (VA/W), backup time, topology (online/line-interactive) and DC/AC choice.

4 min readUpdated: 2026-07-07

UPS selection starts with correctly calculating the load's real power (W) and the required backup time. For critical PLC/control systems a 24 V DC UPS is common; for cabinets an AC UPS.

  • Power — load W + 25% margin
  • Time — controlled shutdown vs long runtime
  • Topology — online (double-conversion) for sensitive loads
  • DC vs AC — 24 V control system or cabinet supply
To allow a controlled shutdown, connecting a 'power lost' signal (relay/digital output) from the UPS to the PLC is recommended.

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