Before a UPS maintenance window

The method of procedure

The method of procedure (MOP) is the script for the window. Agree it in writing before the day:

If the diagram, the labels and the actual breaker positions disagree, the window stops until they agree.

Check the redundancy is still there

A frame installed as N+1 becomes N the day the load grows into the spare module, and nothing alarms. Before the window, compare the measured load on each phase with the capacity left after removing the largest module or unit. If the answer is less than the load, the work needs the maintenance bypass or a temporary unit instead, and the MOP has to say so. The redundancy guide covers the check.

Check the generator

While the load is on bypass, a utility drop reaches it directly. Confirm the generator’s last test date and the transfer switch position before the window, and keep the window short. Count usable fuel, not tank size: fuel below the pickup, a delivery that depends on one supplier, or a test that burned a day’s worth all shorten the real runtime.

The week before

• Battery readings: pull the last report. A block that has drifted more than 50% from its baseline needs a decision first ^[5].
• Event log: note any open alarms, so the technician does not chase an old one.
• Access: escort, loading dock, permits and lockout rules booked.
• Monitoring: tell the NOC which alarms the window will raise, and for how long.
• Stakeholders: IT and facilities sign off on the window and the rollback.
• Parts: fans, capacitors or batteries due on the last report ordered, so they arrive for the same window.

On the day

Run the site’s daily checks first: air intakes and exhaust clear ^[6], and the normal-operation indicator on. A red alarm indicator before the window starts is a reason to stop and call service ^[7]. Then follow the MOP, hold point by hold point.