Most of it, yes. Inspection, readings, battery measurements and the thermal scan run with the UPS online and the load protected. Cleaning, torquing and calibration inside the UPS need a maintenance bypass, which keeps the load powered but on unprotected utility power, or, on a single UPS with no bypass, a planned shutdown.
The difference is planning: knowing which tasks need the load off the inverter, how long that lasts, and whether the site’s design lets one UPS be serviced while another carries the load.
Can UPS maintenance be done without shutting down?
UPS preventive maintenance in Canada: the eight checks we do on APC, Eaton, Vertiv and other UPS systems, what each one tells you, and what a minor maintenance includes compared with a major one.
Chapters: 0:00 Intro · 0:13 Why it matters · 0:35 Check 1. The plan · 1:03 Check 2. The room · 1:16 Check 3. The event log · 1:31 Check 4. The batteries · 2:19 Check 5. The parts that wear out · 2:51 Check 6. The tests · 3:11 Check 7. The major maintenance · 3:45 APC and Schneider Electric · 4:05 Eaton and Powerware · 4:23 Vertiv Liebert · 4:41 Check 8. The report · 5:03 Recap: minor vs major maintenance · 5:42 Our services
Chapters and transcript
Intro
A UPS keeps your equipment running when the power fails, but only if it’s maintained. This is what a maintenance visit covers: the eight checks we do on APC, Eaton, Vertiv and other UPS systems.
Why it matters
Why does it matter? At one government office, the display said more than two hours of backup. When we tested the batteries behind it, six strings out of eight had failed. Here’s how we catch that before the power goes out. The plan, the room, the event log, the batteries, the parts that wear out, the tests, the yearly major maintenance, and the report.
Check 1. The plan
Check one happens before we arrive: the plan. We settle three things with you. When we can work, whether the UPS can go on bypass, and who signs off on any test. On bypass, your equipment runs straight off building power, with no battery behind it. A hospital in the Quebec City region asked whether the visit would put their UPS on bypass. Our advice: do it online, so their equipment stays protected. Most of the visit works that way.
Check 2. The room
Check two: the room. We look at the temperature, the airflow and the dust. Heat takes years off a set of batteries. At that same office, heat was building up in a poorly ventilated room.
Check 3. The event log
Check three: the event log. It shows the recent power failures, every switch to battery or bypass, and the alarms nobody saw. There, the log showed eight power failures in eight months. That UPS had been working hard.
Check 4. The batteries
Check four: the batteries. On APC, Eaton and Vertiv UPS alike, this is where we find most problems. We look for swollen cases, acid at the vents and corrosion on the terminals. Then we measure every block, one by one: its voltage and its internal resistance. Internal resistance tells us more than voltage does. A block whose resistance is much higher than its neighbours is failing, even when its voltage looks normal. The display only estimates runtime. It doesn’t measure each block the way we do. At that office, six of the eight strings failed the test. There was acid at most of the vents, and the batteries were only four years old. Standard UPS batteries last three to five years. Long-life ones can go eight years or more, in a cool room.
Check 5. The parts that wear out
Check five: the parts that wear out. Fans, air filters and capacitors. Before we open a door on a running UPS, we read its arc-flash label and suit up to match it. A clogged filter makes the UPS run hot, so we clean it or replace it. With the UPS carrying your load, and the covers off in full protective gear, we scan the connections with a thermal camera. A loose connection shows up hot long before it burns. The more load on the UPS, the better it shows.
Check 6. The tests
Check six: the tests. If the batteries passed, and you agree, we switch the UPS to battery for a short test. That shows it picks up the load cleanly. If the batteries failed, we skip it. We don’t gamble with your equipment. A short test doesn’t prove your full runtime. If you need that number, we plan a timed runtime test with you.
Check 7. The major maintenance
Check seven: the major maintenance. Everything so far is the minor maintenance, done with the UPS online. Most sites also need a major one each year. It’s the one time your equipment runs without the UPS behind it, so we plan the window with you. We move the load to the maintenance bypass, isolate the UPS and its batteries, lock them out, and test for voltage before anyone works inside. Then we check the torque on the power connections, clean out the dust and change the filters. Before your load goes back on, we run the UPS through each operating mode.
APC and Schneider Electric
Each brand has its own weak spots. On an APC Symmetra PX or LX, the batteries slide out as modules, so we can swap them with your equipment still running. Schneider Electric stopped servicing the APC Galaxy 3500 in 2023. We still maintain them, and we help you plan the replacement before parts get hard to find.
Eaton and Powerware
Eaton’s 9155, 9355 and 93PM often keep their batteries in separate cabinets, in several strings. We test every string on its own. On older Eaton and Powerware units, capacitors and fans wear out with age. We replace them on a schedule, before they fail.
Vertiv Liebert
A hospital can have a whole fleet of Liebert GXT units. We test every one, then plan the replacements by age and result. On three-phase units like the Liebert EXM, it’s the full eight checks. Mitsubishi, Toshiba, Tripp Lite: we service them all, and you get the same report.
Check 8. The report
Check eight: the report. You get it in writing. Every reading, photos and thermal images, and a green, yellow or red rating for each unit. Then a short list of what to do next, starting with the most urgent. For that office, the batteries came back red: replace them now. And since the UPS itself was seventeen years old, we told them to start planning a new one.
Recap: minor vs major maintenance
To recap, here’s what each visit includes. A minor maintenance keeps your UPS online. We check the room, the log, the readings and every battery block. Then the parts that wear out, a thermal scan, and a short test if the batteries pass. A major maintenance adds a planned window on bypass. The UPS and batteries are isolated and locked out, the torque is checked, the inside is cleaned, and every operating mode is tested. Both end with a written report. If your batteries are four years old or more and nobody has tested them, have them tested before your next outage.
Outro
GDF Technologies does this visit across Canada. We offer support when you need it, and when something fails, we’re there day or night. We also offer extended warranties on parts and labour. And when it’s time for a new UPS, we do the consulting and engineering with you, from configuration to delivery and installation. Call us, or ask for a quote at gdftech.com. You’ll hear back within four business hours.
Online, internal bypass, maintenance bypass or shutdown
A UPS can be in four states during a maintenance visit. For the load, the only question that matters is whether the inverter and the batteries are still between it and the utility.
| State | What feeds the load | If the utility fails | Used for |
|---|---|---|---|
| Online (normal operation) | The UPS inverter | The batteries carry the load | Inspection, readings, battery tests, thermal scan, self-test |
| Internal (static) bypass | Utility power, through the UPS’s own bypass switch | The load is unprotected | The UPS’s own reaction to most internal faults; battery swaps on some modular frames |
| Maintenance bypass (built in or external) | Utility power, through a manual path that goes around the UPS | The load is unprotected | Work inside the UPS: cleaning, torque checks, calibration, part replacement |
| Shutdown | Nothing: the load is off | Not applicable | A cold restart after a fault, decontamination of the installation |
Small UPS units often have no internal bypass at all. Schneider Electric notes that systems above single-phase capacities, roughly 20 kW, have internal static bypass switches. A maintenance bypass can be built into the UPS or installed as a separate wall panel. In the design Schneider describes, it is fed from the same panel as the UPS, connects to its output panel, and can only be closed while the UPS is already on static bypass, which is how a technician moves the load onto it with no interruption. Each bypass path and its alarms are covered in our guide to bypass on a UPS.
What gets done with the UPS online
A minor maintenance visit is done entirely in normal operation, and so is the first part of a major one. With the load still on the inverter, our technicians cover:
- the room: temperature, dust, leaks and ventilation, plus access, clearance and electrical hazards;
- the display and the event log: utility outages, transfers, faults and the last self-test;
- input and output voltage and frequency per phase, current, load in percent and in kW, and load balance, measured and compared with what the display shows;
- fans, filters, connectors, control wiring and capacitors, looking for bulging or leaks;
- the batteries: swelling, acid at the vents and corrosion, then the string float voltage, the voltage and internal resistance of every block, and the battery temperature;
- a thermal scan of modules, connections, breakers and PDUs under load;
- with your approval, a self-test or battery transfer test, recording the runtime and whether it holds.
Order matters. The thermal scan is taken with the load applied, so it comes before any step that moves the UPS to bypass. Every maintenance visit ends with a written report: the readings per unit, photos and thermal images, a green, yellow or red status, numbered recommendations, and whether the UPS was online and in working order when the technician left.
Why bypass is not a safe mode
Asking for maintenance “in bypass” sounds cautious. It is the opposite. On bypass the load is fed straight from the utility, with no battery behind it and no conditioning of the power, so a utility outage during the work reaches the equipment. That is why our reports state the rule plainly: maintenance in bypass leaves the load unprotected, so online maintenance is preferred for critical loads.
Schneider Electric puts a number on it for a single-UPS design: maintenance of the UPS, its batteries or the downstream equipment exposes the load to unprotected power at least once a year, typically for 2 to 4 hours.
Field example. A hospital asked whether its annual visit would be done in bypass, because its UPS, a 15 kVA three-phase unit, feeds critical public-health services. We advised doing it online, because in bypass the load is unprotected. Every result came back green: the self-test passed, the display showed 178 minutes of runtime at 15 percent load, and the room was at 21 °C.
Bypass also has a protective job of its own. In most internal failures, a UPS protects the load by moving it to its internal bypass rather than dropping it. A UPS found on bypass is telling you something; the bypass guide explains how to read it.
Work that needs maintenance bypass or a shutdown
A major maintenance visit adds the work that cannot be done on a live power section. The UPS is transferred to maintenance bypass, shut down, locked out and verified dead. Then:
- every nut, bolt, screw and connector is checked for tightness and discoloration, and the terminals are torqued and inspected;
- the inside is vacuumed and cleaned, and the air filters are replaced.
The UPS is then restarted while the load stays on maintenance bypass, so that:
- the rectifier, inverter, static switch and logic circuits are calibrated and checked;
- every operating mode is checked, and the battery charge and discharge is verified.
The load goes back on the UPS only after these checks.
Other jobs need the same kind of window:
- Consumables at end of life. Air filters, fuses and fans are replaced when worn. On one remote site, worn power-module fans were scheduled for the next shutdown.
- Repairs after a failure. After a capacitor failure on an older 300 kVA-class frame, all 90 capacitors were replaced while the load stayed on the external maintenance bypass, unprotected.
- Battery replacement, depending on the design. On a modular frame we transferred the UPS to internal bypass, installed 16 new battery units and brought it back online without dropping the load. On a fleet of single-phase units, battery packs stacked under or over other equipment meant a swap could need a shutdown, so we recommended giving each UPS its own shelf.
- Decontamination. Cleaning a dusty installation was done in a planned shutdown with the site electrician: lockout, plastic containment front and back, HEPA filtration and PPE.
- Restart after a fault. When a UPS has faulted and the load has been running on static bypass since, the cold restart is planned in a full shutdown window, followed by the inverter diagnosis.
Task by task: online or not
| Task | With the UPS online | Needs maintenance bypass or a shutdown |
|---|---|---|
| Room, access and hazard check | Yes | No |
| Display and event log review | Yes | No |
| Voltage, frequency, current, load and balance readings | Yes | No |
| Battery inspection, float voltage, block voltage and internal resistance | Yes | No |
| Thermal scan of modules, connections, breakers and PDUs | Yes, with the load applied | No |
| Self-test or battery transfer test | Yes, with your approval | No |
| Torque and inspect terminals | No | Yes |
| Vacuum and clean inside, replace air filters | No | Yes |
| Calibrate rectifier, inverter, static switch and logic | No | Yes |
| Check every operating mode | No | Yes, transfers to battery and to bypass |
| Fan replacement | On N+1 systems, one module at a time | On a single-module UPS, yes |
| Capacitor replacement after a failure | No | Yes |
| Battery replacement | On some modular frames, through internal bypass | Where packs cannot be reached safely, a shutdown |
| Decontamination | No | Planned shutdown with containment |
How the maintenance window is planned
When part of a visit needs bypass, the window is agreed before anyone arrives:
- Decide with the customer which tasks run online and which need maintenance bypass, which loads are critical, and who approves each test.
- Warn whoever watches the alarms, or pause the monitoring, so a planned transfer does not set off a call-out.
- Book the bypass part outside business hours when the load cannot accept the exposure during the day. Our base service covers business hours (5×8), with a 7×24 option for after-hours visits.
- Check the generator. Our 2026 report template records whether the site has an automatic, manual or no generator and whether it is tested, and field reports have found auto-start generators with no routine test programme.
- Transfer in order: the UPS to static bypass, then the maintenance bypass closed, then the UPS isolated. The return is the reverse, ending with the UPS confirmed online with no active alarm.
Redundant designs: servicing one UPS while another carries the load
How much of a visit can stay on protected power depends on the design. Schneider Electric’s White Paper 75 compares the five standard configurations:
| Design | During maintenance |
|---|---|
| Capacity (N) | No. Maintenance of the UPS, its batteries or downstream equipment exposes the load to unprotected power, usually at least once a year, typically 2 to 4 hours each time. |
| Isolated redundant | Either module can be serviced by moving the load to the other; the whole system still needs a 2 to 4 hour shutdown a year for system-level maintenance. |
| Parallel redundant (N+1) | One module can be removed from the bus and repaired without connecting the load to straight utility. Work that extends beyond a single module or its batteries can still expose the load. |
| Distributed redundant | Concurrent maintenance of all components, if all loads are dual-corded. |
| System plus system (2N, 2N+1) | UPS modules, switchgear and distribution can be maintained without transferring the load to bypass. In 2(N+1), UPS redundancy remains even during maintenance. |
That is why our 2026 report template records whether the site has an external bypass and which redundancy it uses (N+1, 2N). Without a maintenance bypass, work inside a single UPS means a shutdown; with one, it means a planned bypass window. If you are replacing the UPS anyway, an external maintenance bypass lets the new unit go in without a shutdown.
Opening a running UPS safely
Online maintenance means a technician works close to live parts, which is governed by CSA Z462, the Canadian workplace electrical safety standard. As described in a 2021 summary of the standard, CSA Z462 exempts testing, troubleshooting and voltage measuring, and thermography or visual inspection that does not cross the restricted approach boundary, from the energized electrical work permit, as long as the qualified person uses the safe work practices and PPE the standard requires.
Battery work follows a stricter rule in our procedures: the battery breaker and the DC strings are isolated before batteries are replaced or their connections are worked on, and while they are isolated the UPS has no battery behind it. Working online is a matter of procedure and PPE, not a reason to drop the load.
Skipping maintenance to avoid downtime
Vertiv analyzed its own service records, 185 million operating hours for more than 5,000 three-phase UPS units. Its model puts the mean time between failures of units with two preventive maintenance visits a year at 23 times that of units with none. This is Vertiv’s estimate for its own installed base, and it re-affirms the long-held industry belief that more visits substantially increase reliability. The gain depends on the technician: for one with a technician-caused failure in every 100 visits, Vertiv’s model shows reliability improving only up to one visit a year. On batteries, Vertiv reports zero system outages due to bad batteries where they were professionally maintained and remotely monitored.
Our own reports show what the visits catch. Across 150 written GDF service reports, batteries at or past end of life appear in 35 percent, a room too hot, poorly ventilated or contaminated in 24 percent, and acid leaks, corrosion or sulphation in 23 percent.
NFPA 70B, the US standard for electrical equipment maintenance, moved from recommendations to mandatory language in 2023: a specific electrical maintenance program is required, with intervals set from the equipment’s physical condition, criticality and operating environment.
Frequently asked questions
Is the load protected while the UPS is on bypass?
No. On internal or maintenance bypass the load runs on utility power with no battery behind it, so a utility outage during that time reaches the equipment. For critical loads, every task that allows it is done online.
Can UPS maintenance be done at night or on a weekend?
Yes. Our base service covers business hours (5×8), and a 7×24 option covers after-hours visits for the part of the work that needs bypass.
How long does the load stay on bypass during maintenance?
Only during the major part of the visit. For a single-UPS design, Schneider Electric gives a typical exposure of 2 to 4 hours, at least once a year. In an N+1 system, one module can be serviced while the others carry the load.
Will you simulate a power failure during maintenance?
Only with your approval. The self-test or battery transfer test moves the load to the batteries and shows whether the runtime holds; the result is recorded in the report.
Can UPS batteries be replaced without a shutdown?
It depends on the design. On a modular frame we replaced 16 battery units through internal bypass without dropping the load, which was unprotected during the swap. Where battery packs are stacked under or over other equipment, a swap may need a shutdown.
Is there any risk of losing power during maintenance?
Some. Vertiv’s study notes that every service event introduces the possibility of service-related human error, and while the UPS is on bypass the load has no battery behind it. That is why transfers are planned, approved by you, and kept to the part of the visit that needs them.
How often should a UPS be maintained?
Schneider Electric notes that maintenance usually takes place at least once a year. In the United States, NFPA 70B sets the interval from the equipment’s condition, criticality and environment rather than one number for every site. Our contracts list the number of minor and major visits per year for each unit.
Plan your UPS maintenance without dropping the load
Send us the UPS model, its rating and whether the site has an external bypass or a redundant module, and we will tell you which parts of the visit run online and whether a bypass window is needed. See our UPS preventive maintenance service and how a maintenance contract sets the minor and major visits per year, contact GDF Technologies or call 514-252-8324.
Related: replacing Symmetra PX battery modules without an unexpected shutdown and when to replace your UPS batteries.
Written by Christian Barkley, Director, GDF Technologies.
Sources
- GDF Technologies, written service reports, 2026 report template, maintenance procedures and service agreements, 2016 to 2026 (150 written reports; cases described without client, site or date).
- Schneider Electric, White Paper 75, Comparing UPS System Design Configurations, Rev 4, K. McCarthy and V. Avelar. Bypass paths, maintenance bypass, exposure during maintenance, N, isolated redundant, N+1, distributed redundant and system plus system designs.
- Vertiv, The effect of regular, skilled preventive maintenance and remote monitoring on critical power system reliability. MTBF model by number of PM visits; battery outages with maintenance and monitoring.
- D. Colombo, A New Standard for Electrical Equipment Maintenance, EC&M, Oct. 10, 2023. NFPA 70B (2023): mandatory language, electrical maintenance program, condition-based intervals.
- T. Becker, Energized Electrical Work Permit YES or NO?, Electrical Industry News Week, November 11, 2021. CSA Z462 permit exemptions for testing, measuring and thermography.
