Load bank testing
A UPS load bank test is a sequence of transfers, load steps and checks written down before anyone arrives on site. This page sets out what the site must provide and the procedure step by step, as a UPS maker publishes it.
The site must be able to carry the extra load, give the load bank somewhere to shed its heat, and have a qualified person make the connections. In practice that means:
| What happens | What is recorded |
|---|---|
| Infrastructure check: the site can carry the critical load and the test load together | The check, and the approval to proceed |
| Critical load transferred to bypass, then to maintenance bypass | Transfer times and any alarms |
| UPS modules shut down; lockout tag-out | Who applied the locks |
| Load bank connected to the UPS output by the electrician | Connection points and cable route |
| UPS restarted and transferred to normal, on the load bank | UPS status and alarm log |
| Load at 50% for one hour | Voltage, current, regulation; infrared and power-quality readings in a performance test |
| Load at 100% for 3 hours | The same readings, at full load |
| Battery discharge by opening the rectifier input, up to 4 minutes | UPS parameters during the discharge; battery cabinet scan |
| Rectifier input restored; batteries recharge | Recharge behaviour |
| Transfers to bypass and back, repeated three times | Whether each transfer was clean |
| Load removed, load bank isolated and disconnected, locks removed | Completion of each step |
| Critical load returned from maintenance bypass to normal | Final UPS status; the report follows |
The electrician and the site's own personnel, after the infrastructure check. Eaton's method makes this approval its second step: nothing is transferred until the people responsible for the site agree that it can carry both loads. The written method also names who can stop the test and what readings would make them stop it.
Because a single clean transfer proves little. After the load steps and the battery discharge, Eaton's method transfers the UPS to bypass and back to normal and repeats the transfer three times, under the test load, before the load bank is removed. A transfer that fails or misbehaves on the bench is far cheaper to find than one that fails during an outage.
A full working day for the test itself. The load steps alone take one hour at 50% and 3 hours at 100%; add the transfers to and from maintenance bypass, the connections, the battery discharge of up to 4 minutes and its recharge, and the repeated transfers. Some UPS need longer steps or more of them: the maker's method for that model decides.
Thermal and power-quality readings. Eaton's performance-test scope runs the same load steps with an infrared scan of the UPS and battery cabinets at each step and during the battery discharge, and a power-quality meter on the UPS output recording voltages, currents and harmonic content. Hot spots are recorded with their actual temperatures, and thermographs go into the written report.
The critical load runs on maintenance bypass, which means utility power without UPS conditioning. On some UPS the batteries are not available in maintenance bypass, as Schneider Electric notes for the Galaxy VS. The test window is chosen with that in mind: away from known utility work and storms, and with the generator ready.
The procedure follows the UPS maker's method for that model; it is written and agreed with the site before the visit, including the stop criteria and who signs off each step.
Yes. In Eaton's method a certified electrician makes the connections from the load bank to the UPS before testing and removes them afterwards.
Enough to reach a place where its heat can be rejected safely. Eaton's scope supplies 50 feet and adds more on request.
The test stops at the step where it happened, the load returns to a safe state as the written method sets out, and the finding goes in the report with what it needs.
Sources, checked 2026-10-04:
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