What actually happens at UPS commissioning

Most sites treat commissioning as a formality between delivery and handover — the engineer arrives, the machine hums, everyone signs. That is an installation check. Commissioning is the process that proves the machine does what the order said it would, on your floor, with your load, and it produces numbers rather than a signature.

The reason to care is unglamorous. Almost every UPS failure we are called to in the first three years traces back to something that could have been caught on day one: a loose termination, a battery bank that was never discharged, a transfer that was never actually observed on a scope, an earthing arrangement that nobody measured.

Before anyone energises anything

• Insulation resistance on every winding and on the incoming and outgoing cables, recorded — not "checked".
• Phase rotation verified at the input terminals. Getting this wrong on a three-phase machine is a two-minute check that prevents a very expensive afternoon.
• Every termination torqued to the specified figure and marked. Loose terminations are the single most common cause of heating faults, and they are invisible until they are not.
• Earthing and bonding measured, including the neutral–earth arrangement. This is the one most often skipped and the one that causes the most confusing faults later.
• Battery bank: polarity, inter-cell link torque, individual cell voltages recorded before the bank is put on charge.

With the machine running, no load

Output waveform on a scope, not on the front panel. The panel tells you what the controller believes; the scope tells you what the load will actually see. Output voltage and frequency regulation are checked against the design figures rather than against "looks about right", and the input current and power factor are recorded so there is a baseline to compare against in two years.

Stepped load, which is where commissioning earns its name

A resistive load bank at 25, 50, 75 and 100 percent of rated capacity, with readings logged at every step. This is the part sites are most often talked out of, usually because a load bank is not on site, and it is the part that matters most — a UPS that is fine at 30 percent and unstable at 90 has told you nothing until you take it to 90.

Then a thermal soak: held at rated load until temperatures stabilise, followed by a thermal scan of the power stage, the busbars and the joints. Anything running hot at commissioning will be running hotter in May.

Transfers, observed rather than assumed

Mains to battery, battery to mains, bypass in and bypass out — each verified on the scope. A front-panel LED confirms the controller changed state. It does not confirm the load rode through. On a double-conversion machine there should be nothing to see at the output at all, and that absence is the result you are looking for.

Battery discharge, at rated load

Discharge the bank at rated load and time it. This is the only way the backup figure on your certificate becomes a measured number rather than a calculation from the cell datasheet. A bank that calculates to twenty minutes and delivers eleven is not unusual, particularly if it sat in a warehouse before delivery.

What you should be handed at the end

• The test record with actual readings at each load step, not a tick-box sheet.
• The measured battery discharge time at rated load, with the date.
• Thermal scan images or readings for the power stage and joints.
• The as-installed single-line diagram, marked up if it differs from the drawing.
• Settings as left: voltage, frequency, transfer thresholds, charger float and boost voltages.
• The date the next battery discharge test is due.

Keep it. When the machine misbehaves in year three, the commissioning record is the only thing that tells you whether the behaviour is new or whether it was always like that.