On-line, off-line, line-interactive: what is your UPS obliged to report?

Your specification gives the kVA and the minutes of autonomy. It does not say whether the uninterruptible power supply is on-line, off-line or line-interactive. That missing line settles one thing only, and it is the one that matters at two in the morning: whether the supervision system is obliged to tell you how many minutes are left, or may simply report that the load has gone over to battery.

Three topologies, three different lists

ETSI ES 202 336-3 V1.1.1, published on 23 October 2009 by the Environmental Engineering technical committee and downloadable at no cost, is the information model for AC uninterruptible power systems: “The present document applies to monitoring and control of AC UPS power systems for telecommunication equipment.” It does not describe the machine: it describes what the machine must expose to whoever watches it from a distance.

And there is not one list. There are three annexes, all normative: annex A for on-line units, monolithic and modular; annex B for off-line units; annex C for line-interactive ones. Inside annex A the columns multiply again by electrical configuration: single phase on both sides, three phase in with single phase out, three phase throughout. Every cell carries M or NM; a blank cell means no requirement for that type. So compliant with ES 202 336-3 is not information on its own: it becomes information once the annex and the column are named beside it.

The same entry, three opposite outcomes

Take the entry that counts once the mains has gone: “Estimated remaining battery autonomy (time) during discharge”. On an on-line unit with three phase in and three phase out, and on every modular configuration, it is M. On the same on-line unit, monolithic and with a single phase output, NM. On an off-line unit, NM. On a line-interactive one, NM.

In the battery information model that same entry stays outside the mandatory minimum. Here, in one case and one only, it moves inside: the upstream link can be bound to tell you what the downstream link never has to provide — but only if you wrote the right topology.

The same pattern governs the command “Battery test on demand”, mandatory only on three-phase on-line units and on modular ones, and the alarm “Battery test failure”, mandatory in every column of annex A and not mandatory on off-line and line-interactive units: two compliant machines that may never report a failed test.

One thing never changes. The detailed record — “Detailed battery test data record : discharge chart, temperature, string current, cell voltages” — is NM in all three annexes, in every column: the verdict can be mandatory, the curve that proves it never is.

Who tells you the load is running uncovered

The document sets out two bypasses; the static one switches by itself, the external one is closed by a person: “External (Manual) Bypass that transfers input voltage to the output to supply Current using equipment, in the case of UPS failure, UPS service, maintenance, etc.” While the load sits there, nothing stands between the mains and the equipment.

The alarm that says so is “Load is supplied from manual by-pass”. Mandatory on three-phase on-line units and on modular ones; not mandatory on the two monolithic configurations with a single phase output, nor on off-line, nor on line-interactive ones. An engineer closes the external bypass for maintenance and does not open it again: on a good many compliant machines, nobody in the control room is obliged to see it.

Further upstream still, the model measures nothing

ETSI ES 202 336-5 V1.1.1, published on 7 April 2010 by the same committee and likewise free, does the same job for the diesel standby generator. It carries a single normative annex, table TP1, the “minimum set of monitored information”. The mandatory alarms are numerous: low level in the fuel tank, start failure, safety stop, undetermined stop, fuel leakage, engine start inhibited, starting battery failure.

Against the Measurement and Calculated value rows, that table carries a single word: “None”.

No mandatory measurement at all. Not the fuel in litres, only the low-level threshold. Not output voltage, current or frequency. Not the running hours. And “Remaining autonomy (running time) of generator”, an assessment built on fuel consumption and reserve, sits in annex C, which is informative. So does the test that actually counts: “Running test failure”, where the text says the trial “switches the load on the generator even if the main is present”.

The picture is this: the standby chain is obliged to tell you it has failed, and almost never how much you have left.

What to specify, what to check

One rule helps: when an optional alarm requiring a parameter set is present, “the corresponding parameter set is mandatory in the control section in order to allow remote adjustment under appropriate login procedure”. Asking for an optional entry drags its threshold along, remotely adjustable.

In the specification: the topology written out in full and the phase configuration, because those choose the annex and the column; the optional entries promoted to contractual obligations — remaining autonomy during discharge, the test command, the detailed test record, the alarm for load on manual bypass; for the generator, fuel as a measurement and not only as a threshold, the running hours, and the test that switches the load over with the mains present, with its report. And one line more, because the document asks for it: “Parallel operation of UPS systems is outside the scope of the present document.” Units in parallel have to be specified separately.

At acceptance you open the annex for the machine delivered — not any annex at all — and tick off, entry by entry, what reaches the supervision system, not what appears on the local display. The accuracies are written down: input phase voltage ±2 V, frequency ±0,1 Hz, currents ±2 %, battery voltage ±1 V, estimated remaining capacity ±5 %.

What we do not know

We have read ES 202 336-3 V1.1.1 and ES 202 336-5 V1.1.1 in full, downloaded on 20 September 2026, and checked number, version, date and status on the ETSI Work Programme: both come back as “Publication”, dated 23-10-2009 and 07-04-2010, neither harmonised. We have not read part 1, the generic interface, which both cite normatively: its V1.3.1 revision has been published since 10 April 2025 and the Work Programme record states “This revision will consider the impact on the structure of the remaining parts (2 to 11)” — the XML structure in part 3 may no longer be aligned. The figures are images inside the PDF and we take no values from them. IEC EN 62040 on UPS, cited in the bibliography of part 3, and the CEI and EN installation standards are paid documents: we have not read them and we report nothing from them, the topology definitions included, which we call by the names the ETSI document uses. An ETSI Standard binds where the contract invokes it: we have not checked whether any Italian provision makes it compulsory in network procurement.

The two axes, on a continuity that is only declared

First axis: in the specification we vet the UPS topology stops being implicit, the applicable annex is named and the optional entries become clauses; at acceptance it is checked, point by point, that they really reach the supervision system, with the report and documentation handed over together with the plant.

Second axis: one alarm on its own says nothing, a series says a great deal. With CSIDIA, the other company in the group, bypass states, transfers, generator test reports and readings along the chain become a single map of the site, where an AI recognises the drift — the manual bypass left closed after a visit, the load test that grows further apart — and the team closes the problem before the outage. It runs on-premise or in a dedicated cloud with data centres in Italy, under shared management, for a data centre as much as for a network exchange.

A site visit, at no cost, produces the list of your standby links: real topology, applicable annex, which entries reach the supervision system and which stop at the display. Talk to one of our engineers: a closed bypass makes no sound, and a continuity that is declared is not a continuity that has been proved.