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A UPS keeps only the equipment plugged into its battery-backed outlets running. When a switch stays lit during an outage, that shows its own power path held. It does not show that the router, the modem or fiber terminal (ONT), or the provider’s network stayed up. That is the most likely reading of the depot outage described here, but the report is one reported experience. The wiring, the battery condition, and the provider’s status for that day were not recorded, so the explanations below are checks to make, not a confirmed diagnosis.
What a UPS protects and what it leaves out
Schneider Electric’s UPS buying guide describes a UPS as “a battery backup system that provides instant emergency power during outages and protects connected devices from power spikes and failures.” The word that matters is connected. Battery power reaches only the devices on the outlets the battery supports. Many units also have outlets that offer surge protection without battery backup. A router on one of those outlets loses power the moment mains power fails, even though the UPS itself is working.
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That gives you two separate layers to check:
- Local power: whether each device in the connection path received battery power during the outage.
- End-to-end service: whether the modem or ONT could still reach the provider’s network, and whether the provider’s own equipment was up.
A lit switch answers only the first question for the switch. It says nothing about the second.
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The reported sequence (switch on, router dark) is consistent with several causes. Each leaves a different trace, so you can test them rather than guess.
#1 Best Overall
- 425VA/260W Standby Uninterruptible Power Supply (UPS): Uses simulated sine wave output to provide battery backup power and to safeguard home office, home entertainment including computers, gaming consoles, and broadband routers
- 8 NEMA 5-15R OUTLETS: Four battery backup & surge protected outlets; Four surge protected outlets; INPUT: NEMA 5-15P right angle, 45 degree offset plug with five foot power cord
- ADDITIONAL FEATURES: LED status light indicates Power-On and Wiring Fault, transformer-spaced outlets
- GREENPOWER UPS HIGH EFFICIENCY DESIGN: Reduces power consumption by utilizing a compact charger and power inverter to create an ultra-efficient backup power system for home and office use
- 3-YEAR WARRANTY – INCLUDING THE BATTERY; 75K USD Connected Equipment Guarantee; UL SAFETY CERTIFIED: Product has been tested in a UL certified lab and listed with UL as meeting or exceeding safety standards
| Possible cause | What it would look like | How to check |
|---|---|---|
| Router or ONT on a non-battery outlet | Switch stays lit; router and ONT go dark at the moment mains fails | Trace each cable to its outlet. Compare against the UPS manual’s outlet labeling, which shows which outlets are battery-backed. |
| UPS overloaded or dropped load | Runtime far shorter than expected, or the unit shut down under load | Compare the total nameplate wattage of everything plugged in with the UPS’s watt rating. Eaton cautions that exceeding UPS capacity can cause it to drop the load during an outage. |
| Depleted or failed battery | Short runtime, or a battery or replace-battery alarm on the front panel | Run the unit’s self-test if it has one, and check the battery’s age and replacement history. Not stated for every model; check the manual. |
| Router lost power for another reason | Router’s power light is off, or its adapter is unplugged or on a switched strip | Check the router’s power light, its adapter, and whether its circuit breaker tripped. |
| Provider or upstream outage | Switch and router are powered, but there is no internet | Check the modem or ONT status lights and the provider’s status page. Test from a device on cellular data. |
Map the full connectivity chain before you size anything
Eaton recommends counting every device that has to stay up for connectivity, not only the switch. For a typical closet that means the following:
- List each device in the path from the incoming line to the clients: the ONT or modem, the router, the switch, and any local controller that the network depends on.
- Record which outlet each device uses and whether that outlet is battery-backed.
- Find each device’s power rating on its manufacturer documentation or nameplate. Note whether it uses an external power adapter, since the adapter’s rating may be the figure you need.
- Write the total down. This is the figure you will size the UPS against.
Size by watts, not by the VA number alone
VA (volt-amperes) and watts are not interchangeable. Eaton recommends choosing a UPS whose watt output capacity is above the connected load, and confirming compatibility. Check the watt rating on the unit as well as the VA rating, and stay within the manufacturer’s load guidance.
Rank #2
- KEEP YOUR COMPUTER, WI-FI AND ROUTER RUNNING THROUGH POWER OUTAGES: Supplies short-term battery power during outages to maintain internet connectivity and allow safe shutdown of computer during power interruptions
- POWER PROBLEMS DON'T ONLY HAPPEN DURING STORMS: 23 minutes of runtime (at 100W load) guards against outages, while surge protection shields connected devices from unexpected power events that happen even on a normal day
- PROTECT EVERYTHING ON YOUR DESK: 5 well-spaced outlets with full battery backup and surge protection, plus 2 surge-only outlets for less critical gear
- PHONE CHARGER: Keep your phone charged even when the power's out. The built-in 1.5A USB port works during outages
- EASY BATTERY REPLACEMENT KEEPS COSTS LOW: Swap the internal battery in minutes when it ages out, no need to replace the whole unit (APC replacement battery APCRBC154, sold separately)
- If a device lists only an amp rating, multiply amps by the AC voltage to estimate its load. Eaton describes this method. Because the result is a volt-ampere figure, treat it as a conservative estimate and confirm it with the manufacturer or reseller.
- Add the estimates for every device in your chain.
- Select a UPS whose watt output rating exceeds that total, then check the model’s VA rating, outlet count, and plug and circuit fit for your site.
- If the figures are close, choose the larger unit or confirm with the manufacturer. Eaton warns that an overloaded UPS can drop the load during an outage.
Runtime depends on the load, not the VA label
Do not infer runtime from a VA rating. Use the manufacturer’s runtime chart at your estimated load and the duration you need. Runtime varies with the load and with the specific UPS and battery, so the chart for one model does not transfer to another.
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Rank #3
- 1500VA / 900W RELIABLE BACKUP POWER: The highest VA capacity available for home use; delivers short-term battery power to keep essential devices powered during blackouts, surges, and unexpected power interruptions
- TEN PROTECTED OUTLETS: Power your entire setup with 5 battery backup outlets for essential devices, and 5 surge-only outlets for peripherals. Plus built-in coaxial and Ethernet surge protection for added peace of mind
- AUTOMATIC VOLTAGE REGULATION (AVR): Corrects low voltage brownouts (88V+) and surges (+/-13%) without draining battery. Boosts or trims to stable 120V. Extends runtime for blackouts; Active PFC compatible for gaming PCs
- REPLACEABLE BATTERY & ENERGY STAR UPS: User-replaceable battery (APCRBC124, sold separately) for zero-downtime swaps. ENERGY STAR certified for 92%+ efficiency, cutting energy costs vs standard UPS units
- LCD DISPLAY PANEL: Features an intuitive LCD screen that displays real-time status information including battery charge level, estimated runtime, load capacity, and input voltage for easy monitoring of your power protection system
Eaton describes the same approach as load shedding: “Load shedding allows you to prioritize the battery backup runtime of your critical equipment by automatically turning off nonessential equipment during longer outages.” When a closet needs more time than the UPS provides, the options are a compatible external battery module, a generator plan, or load shedding. Confirm that any external battery is compatible with your specific UPS before buying it.
What to compare when choosing a UPS
- Total measured load and the watt headroom above it
- Runtime at your expected load, taken from the manufacturer’s chart
- Battery age, and whether the battery is user-replaceable
- Number and type of battery-backed outlets
- Plug, voltage, and circuit compatibility with the closet’s power
- Rack or desktop form factor
- Waveform requirements; Eaton notes that some equipment needs pure sine-wave output
- Remote monitoring and management
- Support for external batteries or load management
Schneider Electric separates basic home and office units from business and enterprise models. Business models may offer network management and extended runtime options. The right class depends on the devices and the site, so compare specific models against your own load list.
Rank #4
- 500VA/300W Smart App LCD Uninterruptible Power Supply (UPS): Uses simulated sine wave output to provide battery backup power to protect department and workgroup servers, network devices, and telecom installations without Active PFC power supplies
- SIX NEMA 5-15R OUTLETS: Four battery backup and surge protected outlets; Two Surge protected outlets; INPUT: 15A, NEMA 5-15P straight plug with 10 foot power cord
- MULTIFUNCTION LCD PANEL: Provides runtime in minutes, battery status, power conditions, alerting users to potential problems before they can affect critical equipment and cause downtime; REMOTE MANAGEMENT: Requires optional RMCARD205 management card
- AUTOMATIC VOLTAGE REGULATION (AVR): Corrects minor power fluctuations without switching to battery power; UL SAFETY CERTIFIED: Product has been tested in a UL certified lab and listed with UL as meeting or exceeding safety standards
- 3 YEAR WARRANTY – INCLUDING BATTERIES; $300,000 Connected Equipment Guarantee
A product example: Eaton SMART1500SLT
Eaton lists the Tripp Lite SmartPro SMART1500SLT as a line-interactive UPS suitable for network devices. Its product page gives the following figures. These are manufacturer-listed specifications, not a recommendation for any particular closet.
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|---|---|
| Type | Line-interactive, listed by Eaton as suitable for network devices |
| Output capacity | 900 W |
| Runtime at full load (900 W) | 8 minutes |
| Runtime at half load | 20 minutes |
| Replacement battery | RBC36-SLT |
Before buying, confirm the current product page, your measured load, the electrical connections, the battery’s condition, and your runtime requirement. The page is the source for these figures, and its date is not stated in the material reviewed.
Best Value
- 1500VA/1000W PFC Sinewave Uninterruptible Power Supply (UPS): Uses sine wave output to provide battery backup power for Active PFC & conventional power supplies; Safeguards computers, workstations, network devices, and telecom equipment
- 12 NEMA 5-15R OUTLETS: 6 battery backup & surge protected outlets, 6 surge protected outlets; INPUT: NEMA 5-15P right angle, 45 degree offset plug with 5 foot power cord; 2 USB charge ports (1 Type-A, 1 Type-C) quickly charge phones and tablets
- MULTIFUNCTION, COLOR LCD PANEL: Displays immediate, detailed information on battery and power conditions; Color display alerts users to potential issues before they can affect critical equipment and cause downtime; Screen tilts up to 22 degrees
- AUTOMATIC VOLTAGE REGULATION (AVR): Corrects minor power fluctuations without switching to battery power; UL SAFETY CERTIFIED: Product has been tested in a UL certified lab and listed with UL as meeting or exceeding safety standards
- 3-YEAR WARRANTY – INCLUDING THE BATTERY; $500,000 Connected Equipment Guarantee; FREE PowerPanel Management Software (Download)
Restart order after an outage
Once power returns, bring the chain back up in the order it depends on:
- Confirm the UPS has returned to normal operation and has no active alarm.
- Power the ONT or modem first and wait for its sync or link lights to settle.
- Power the router, then the switch.
- Test the connection from a wired client, then from a device outside the network. Note whether the problem is local or upstream.
Write down the outage start and end times and which outlets each device was on. That record is what lets you match a future failure to one of the causes in the table above.
Quick Recap
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