Choosing a UPS: Load, Runtime and Maintenance Questions

KEY POINTS

Check both kW and kVA limits against the actual equipment load.
Specify the runtime needed for generator transfer or controlled shutdown.
Plan battery access, bypass operation and replacement costs before purchasing.

A UPS, or uninterruptible power supply, should be selected around what the connected equipment needs to keep doing during a supply disturbance. Begin with the load, the acceptable interruption and the time required to recover or shut down.

Compare the operating types

Eaton’s topology guide describes three common approaches. The specific model’s performance and operating mode still need checking.

Type	Operating principle	Question for the supplier
Standby	Transfers to battery when the incoming supply is outside its operating limits	Can the load tolerate its transfer time and output waveform?
Line-interactive	Regulates incoming voltage and transfers to battery when needed	What input range can it correct without using the battery?
Online double-conversion	Supplies the load through AC-to-DC-to-AC conversion in that mode	What changes in bypass or energy-saving modes?

Online double-conversion operation avoids a transfer interruption when moving from normal input to battery. This does not mean every bypass transition or fault condition is interruption-free. Specify the operating modes that will actually be used.

Define the load and required runtime

Prepare an equipment list with measured or manufacturer-specified demand, phase arrangement, starting behaviour and planned expansion. Check the UPS’s kW and kVA limits, overload capability and compatibility with the load. A larger battery does not increase the inverter’s power rating.

State the purpose of the backup period. Is it to bridge a generator start, support a controlled process stop or close down IT systems? Ask for the manufacturer’s runtime data at the proposed load, including the assumptions for battery condition and temperature. Eaton’s UPS fundamentals handbook is a useful reference for preparing these questions.

Review the installation and maintenance plan

Ask the supplier and responsible engineer to confirm:

Space, ventilation, floor loading, access and environmental limits.
Input and output protection, earthing, cable routes and connection responsibilities.
Compatibility with any generator and the proposed transfer sequence.
Battery chemistry, monitoring, replacement access and disposal arrangements.
The approved bypass and isolation arrangement for maintenance.
Alarm destinations, operating instructions and handover testing.

Compare total ownership costs, including batteries, support and planned maintenance. No battery chemistry removes the need to follow the manufacturer’s installation and temperature limits.

Make acceptance measurable

Agree which operating scenarios will be demonstrated and how results will be recorded. Include normal supply, agreed backup behaviour, alarms and recovery, with a method that protects the connected operations.

ETES’s electrical installation service can be discussed alongside your equipment supplier’s requirements. Share the load list, existing distribution drawings and required backup duration so the connection scope is clear.