Do security cameras still record during a power outage?
Only the parts on backup power keep recording. What stops when the power does, how long a UPS keeps a wired system recording, and what to check when the power comes back.
Technical figures checked against the standards listed at the end.
Security cameras keep recording during a power outage only if the cameras, the network switch that powers them and the recorder all have backup power. Wired cameras run on Power over Ethernet from the switch, so one UPS that carries the switch and the recorder keeps every wired camera recording until its battery runs down: about 2 hours 12 minutes for the example system on this page. Wi-Fi cameras plugged into wall outlets stop with the building, and nothing reaches your phone or the cloud unless the modem and router are on backup power too.
All 12 wired cameras recorded the whole outage.
- UPS runtime on this load
- 2 h 12 min at 117 W
- Wired cameras recorded
- all 90 minutes
- Phone and cloud worked
- none
- Wi-Fi cameras
- off for all 90 minutes
Footage already saved is not lost when the power goes out. What an outage takes is the time it lasts: with no backup power, recording stops, and the recorder's drive takes an abrupt shutdown in the middle of a write. The sections below cover what each part does in an outage, how to work out the runtime of a UPS with real numbers, how to choose and connect one, and what to check when the power comes back.
Every figure uses the same system: a five-story walk-up apartment building with 12 wired cameras (entrance, lobby, mailroom, stair landings, cellar and rear yard). A 16-channel recorder with two drives and a PoE switch sit in a locked cellar closet, with the building's modem and router on the same shelf. Two plug-in Wi-Fi cameras cover a side yard where no cable was run. The power figures are examples for this kind of equipment: recorder 30 W, switch 15 W on its own, cameras 6 W each, modem and router 15 W together. It is an example, not a client's building.
01Do security cameras record during a power outage? Part by part
A camera system is a chain, and an outage breaks it at the first link with no battery behind it. Figure 1 lets you put each part of the example system on a UPS and play the outage through.
Wired PoE cameras
A PoE camera has no power supply of its own. It gets power over the same Cat6 cable that carries its video, from a port on the PoE switch, or on the recorder if the recorder has PoE ports built in. When the switch loses power, every camera on it goes dark at the same moment. That works in your favor: one UPS in the closet carries every wired camera, with no battery at any camera. Our technical guide to PoE security camera installation covers power budgets and cable.
The recorder
The recorder writes the video to its drives: an NVR for IP cameras, or a DVR for older analog cameras on coax (see NVR, DVR and cloud recording compared). On a UPS without the switch, it keeps running with nothing to record. On a UPS with the switch, it records every wired camera exactly as it did before the outage. A recorder with built-in PoE ports makes the cameras and the recorder one load on one plug.
Wi-Fi and battery cameras
A plug-in Wi-Fi camera runs from a wall outlet, so it stops with the building unless that outlet has its own backup. A battery camera keeps running, but with the router down it has nowhere to send its clips unless it also saves them to a memory card. Our comparison of wired and wireless security cameras goes further into both.
Internet, remote viewing and cloud copies
Watching from a phone, alerts and any cloud copy all need the modem and the router, so they stop unless both are on backup power. Even then, the line can drop if the provider's equipment outside the building loses power. A cloud copy protects footage that already left the building; it records nothing while the cameras are dark. Our article on cloud storage compared with a local NVR or DVR weighs the two.
Cameras with memory cards
Many IP cameras can also record to a memory card. If the switch is on backup power and the recorder is not, a camera set to record to its card keeps a copy you can pull later. It is a useful second layer, set up camera by camera, and a card holds far less than the recorder.
It does not take a blackout
On July 13, 2019, a substation fault cut power to about 73,000 customers on Manhattan's West Side, from Times Square to the Upper West Side, for several hours. A tripped breaker on the closet circuit stops a camera system just as completely, and nobody may notice until someone goes looking for footage. In a mixed-use building the closet may share a circuit with another space, or sit on a panel the building staff cannot reach. Label the closet circuit, keep it for the security equipment where you can, and treat any change to it as work coordinated with the electrician.
02What happens to recorded footage when the power goes out
Footage the recorder has already written stays on its drives. An outage does not erase it, and once the recorder is running again it goes back to overwriting the oldest video on its normal loop. Our article on how long security cameras keep footage explains that loop.
What a hard cut can damage is the recording in progress. The last seconds the recorder was holding in memory are lost, and a drive that loses power in the middle of a write can leave the file being written, or less often the recorder's index of its recordings, in need of a repair when it starts again. Recorders are built to recover from this and most do, but every hard shutdown is a risk a UPS avoids.
Two things reduce it further. A clean shutdown: some UPS units can tell a recorder over USB or the network to shut down before the battery is empty, if the recorder accepts that signal. Many recorders do not, so ask before you count on it. And healthy drives: a drive that was already failing is the one most likely to come back with errors.
If you keep footage for a lease, an insurer or your own policy, write down any gap an outage leaves. Our guide to NYC building security rules for cameras and intercoms covers what the law does and does not say about cameras in buildings; it is general information, not legal advice.
03How long will a UPS keep security cameras recording?
A UPS (uninterruptible power supply) holds a battery and an inverter. When building power fails, the inverter turns the battery's direct current into the alternating current the equipment expects, quickly enough that the equipment keeps running. How long it can do that depends on two numbers: how much energy the battery holds, and how fast the equipment uses it. Four steps get you from the equipment list to a runtime you can plan on.
1. Add up the load in watts
Read each device's power from its label or data sheet, or better, measure it: many UPS units show the load in watts on their display. In the example: recorder 30 W, PoE switch 15 W on its own, and 12 cameras at 6 W each, 72 W. The load is 117 W.
Each PoE standard sets a ceiling, not a typical draw. IEEE 802.3af allows up to 12.95 W at the camera (15.4 W from the switch port), and 802.3at allows up to 25.5 W (30 W at the port). A fixed camera often draws well under the 802.3af ceiling, and more at night when its infrared lights come on; pan-tilt-zoom cameras and cameras with heaters can need 802.3at. Size the UPS to the measured draw, and check that the switch's PoE budget covers every camera with room to spare.
2. Find the battery's watt-hours
Battery energy is voltage times amp-hours. The example UPS holds four 12 V, 9 Ah batteries: 4 × 12 × 9 = 432 Wh. The inverter loses part of that as heat. This page uses 85 percent efficiency as an example; a UPS carrying a small fraction of its rating is often less efficient. The basic formula:
runtime = battery Wh × efficiency ÷ load
432 Wh × 0.85 ÷ 117 W = 3.14 hours
3. Correct for how fast you drain it
That formula assumes the battery gives its full rating however fast you drain it. Lead acid batteries do not. Their amp-hour rating is measured over a slow 20-hour discharge. One maker's data sheet for a 12 V, 9 Ah battery lists 0.45 A for 20 hours, but only 5.56 A for 1 hour: about 62 percent of the rating when drained in an hour. Fitting those two points gives a Peukert exponent of about 1.19, and a planning runtime:
planning hours = 20 × (formula hours ÷ 20)1.19
20 × (3.14 ÷ 20)1.19 = 2.21 hours, about 2 h 12 min
The correction is largest for short runtimes. A formula runtime of 1 hour plans at about 34 minutes; a formula runtime of 8 hours plans at about 6 hours 43 minutes. This is an estimate from one battery's data. The UPS maker's runtime chart for your model at your load is the better number, and a battery a few years old gives less than either. Our article on how long security systems last shows what a worn battery does in an outage.
4. Size the battery for the runtime you want
Work backward from a target. For 4 hours at 117 W, the formula hours needed are 20 × (4 ÷ 20)1 ÷ 1.19 = 5.17, and the battery is 117 × 5.17 ÷ 0.85 = 712 Wh. Battery sizing practice treats a lead acid battery as worn out when it falls to 80 percent of its rated capacity, so IEEE 485 adds a 1.25 aging factor: about 890 Wh. That is about twice the example UPS, which is why long runtimes come from external battery packs or a generator rather than one larger box. Figure 2 runs the same four steps on your numbers.
Example: 16-channel recorder, two drives.
Example: fixed camera with infrared on at night.
Swipe the drawing sideways to see the cameras.
30 W recorder + 15 W switch + 12 × 6 W cameras = 117 W
72 W of PoE. 6 W per camera is under the 802.3af limit of 12.95 W at the camera (15.4 W at the switch port).
4 × 12 V × 9 Ah = 432 Wh
432 Wh × 0.85 ÷ 117 W = 3.14 h
2 h 12 min
20 × (3.14 ÷ 20)1.19 = 2.21 h
Correction for a faster drain than the battery rating, from a 12 V 9 Ah data sheet.
20 × (4 ÷ 20)1 ÷ 1.19 = 5.17 h formula time
117 W × 5.17 h ÷ 0.85 = 712 Wh; × 1.25 for aging = 890 Wh
This 432 Wh battery falls short of 4 h.
Open the full UPS runtime calculator for more inputs, a shareable link and the math shown.
Two patterns show up as you change the numbers. A pan-tilt-zoom camera at 20 W counts as more than three fixed cameras at 6 W, so one or two of them can shorten the runtime more than adding a row of fixed cameras. And because the recorder and the switch draw the same with 4 cameras or 24, a small system spends most of its battery on the closet: with 4 cameras at 6 W, the cameras are 24 W of a 69 W load.
04Choosing a UPS for an NVR and PoE cameras
Standby, line-interactive or double conversion
IEC 62040-3 sorts UPS designs into three classes. A standby (offline) UPS passes building power straight through and switches to its inverter when the power fails, which takes a few milliseconds. A line-interactive UPS also corrects high and low voltage without touching the battery, which saves the battery for real outages, and it too switches in milliseconds. A double conversion (online) UPS runs the equipment from its inverter all the time, so there is no switchover at all; it gives off more heat doing it. For a recorder and a switch in a closet, line-interactive is the usual choice. Double conversion fits where the building power is poor or a generator feeds the circuit.
Watts, not only VA
A UPS carries two ratings, one in volt-amperes and one in watts. The load has to stay under the watt rating, and the runtime comes from the battery, not from either rating: two units with the same VA rating can hold very different batteries. Read the battery size, or the maker's runtime chart, before you compare models.
Plug into the right outlets
Some UPS units have two kinds of outlets: battery-backed and surge-only. A recorder plugged into a surge-only outlet goes dark with the building. Plug the recorder, the PoE switch and, if you want remote viewing during an outage, the modem and router into the battery-backed outlets, and label each plug. Our networking service covers the modem, router and switch side of the closet.
Keep the closet cool
Heat does little to the runtime on the day of an outage; the battery data sheet above lists 102 percent of rated capacity at 40°C. What heat cuts is battery life. One UPS maker gives 20 to 25°C as the ideal range and says every 8°C (15°F) above it halves battery life. A UPS in a hot cellar closet or a ceiling space needs new batteries sooner, so put it where air moves and write the install date on the battery. Our pages on data closets and on the cabling and closets behind an integrated security system cover where that equipment should live.
Long outages and building generators
For an outage longer than a battery can carry, the answer is a standby generator. A generator needs some seconds to start and take the load; NFPA 110 classes an emergency power supply that must restore power within 10 seconds as Type 10. The UPS still matters, because it carries the equipment through that gap. Ask whether the closet circuit is on the generator at all, since a generator often carries only some of a building's circuits. Some UPS units reject generator power whose frequency wanders and stay on battery; an input sensitivity setting often deals with that. Connecting the closet to a generator circuit is work coordinated with the electrician. Whether a permit applies depends on the scope and the building; we check during the site visit and say what applies before work is scheduled.
05When the power comes back: what restarts and what to check
Most equipment starts again on its own when power returns, but not all at once, and not always cleanly. Figure 3 plays the restart in the example closet two ways: after an outage the UPS carried, and after one that ran the battery flat.
Swipe the drawing sideways to see the cameras.
Building power returns to a closet that went dark. Everything starts at once, but each part takes its own time. Some UPS units can be set to wait for a minimum charge before turning their outlets back on.
- UPSOn line power, charging
- Modem and routerStarting
- PoE switchStarting
- RecorderStarting
- Wired camerasOff
- Wi-Fi camerasStarting
- Phone appNo connection
After every outage
- CheckRecorder clockCompare the recorder time with your phone. A clock reset after a long cut stamps every new recording with the wrong time.
- CheckEvery camera recordingIn playback, look for new video on every camera after the restore time, not just a live picture.
- CheckDrive statusThe storage page should show every drive as normal. If a drive shows an error or asks to be formatted, do not format it until the footage you need is copied.
- CheckRemote viewingOpen the app on cellular data, away from the building Wi-Fi, and confirm live view and playback.
- CheckUPS chargingLine power on, no alarm, battery charging. Until it recharges, a second outage gets less runtime.
- CheckWi-Fi camerasEach one should show video again. They restart on their own when their outlets get power back.
- CheckWrite down the gapNote when the power went out and came back, and which cameras had no video, for any later incident report.
Why the clock matters
A recorder keeps time through a power cut with a small coin battery on its main board. When that battery is weak, a long cut can reset the clock to a factory date, and every new recording is stamped with the wrong time until someone notices. Footage with the wrong time is hard to find and hard to use. Set the recorder to take its time from the internet (NTP) and the cameras to take theirs from the recorder, and look at the clock after every outage.
If a camera is live but not recording
A live picture proves the camera and the switch are up; it does not prove the recorder is writing. Open playback and look for new video after the restore time on every channel. If a channel is missing or a drive shows an error, do not format anything until the footage you need is exported. A recorder that will not resume is a repair job: see NVR or DVR not recording, and for footage on a damaged drive, security footage recovery.
06Backup power checklist for security cameras
Ask these about your own system, or of any installer who quotes one. Each answer is something you can check in the closet or on the recorder.
- What is plugged into each battery-backed outlet on the UPS, and is anything that matters on a surge-only outlet?
- Is the PoE switch on the UPS, and not only the recorder?
- Are the modem and router on it, if you need remote viewing or cloud copies during an outage?
- What is the measured load in watts, and what runtime does the UPS maker's chart give at that load?
- Can the UPS tell the recorder to shut down cleanly, and has that been set up and tested?
- Is the closet on its own labeled circuit, and is that circuit on the building generator, if there is one?
- When were the UPS batteries installed, and when were they last tested under load?
- Does the recorder set its clock from the internet, and do the cameras set theirs from the recorder?
If you would rather have someone else answer them, we can look at the closet and the recorder and tell you what your system does in an outage. Our security camera installation service includes sizing backup power for the recorder and the switch.
07Security cameras and power outages: FAQ
Do security cameras still record during a power outage?
Only if the cameras, the PoE switch that powers them and the recorder all have backup power. With the switch and the recorder on a UPS, wired cameras keep recording until the battery runs down; the example system in this article gets about 2 hours 12 minutes from a 432 Wh battery at 117 W. Without backup power, recording stops the moment the power does.
Do wireless security cameras work without power?
A plug-in Wi-Fi camera stops when its outlet loses power. A battery camera keeps running, but with the router down it can only save clips to a memory card, if it has one. Remote viewing and cloud uploads also need the modem and router on backup power.
How long will a UPS run an NVR and PoE cameras?
Multiply the battery watt-hours by the inverter efficiency, divide by the load, then correct for a fast drain. For 432 Wh at 85 percent efficiency and 117 W, the formula gives 3.14 hours and the corrected planning figure is about 2.2 hours. The UPS maker's runtime chart at your measured load is the more reliable number.
What size UPS do I need for a security camera system?
Start from the runtime you want. Add up the load in watts, work out the battery watt-hours that load needs for that runtime, then add 25 percent for battery aging. The UPS watt rating has to be above the load, and the battery, not the VA rating, sets the runtime.
Will a power outage erase security camera footage?
No. Footage already written to the recorder's drives stays there. A hard cut can lose the last seconds being written and, less often, leave the recordings needing a repair when the recorder restarts, which a UPS avoids.
What should I check after a power outage?
Check that the recorder's clock is right, that every camera shows new recordings after the restore time, and that the drives report as healthy. Then confirm remote viewing works and that the UPS is back on line power and charging.
Sources and standards
- IEEE 802.3af and 802.3atPower over Ethernet. 802.3af: up to 15.4 W at the switch port and 12.95 W at the powered device. 802.3at: up to 30 W at the port and 25.5 W at the device. Used in Figure 2 as limits, not as typical draws.
- IEC 62040-3Uninterruptible power systems, method of specifying the performance and test requirements: the standby, line-interactive and double conversion classes.
- IEEE Std 485Recommended practice for sizing lead acid batteries for stationary applications: a 1.25 aging factor, so a battery at end of life, 80 percent of rated capacity, still carries the load. As summarized in a battery conference paper on aging factors in battery sizing.
- NFPA 110Standard for Emergency and Standby Power Systems: a Type 10 system restores power within 10 seconds.
- 12 V 9 Ah sealed lead acid battery data sheetRated 9 Ah at the 20-hour rate (0.45 A); constant current discharge to 10.5 V at 25°C of 5.56 A for 1 hour; capacity 102 percent at 40°C and 85 percent at 0°C. Source of the 1.19 Peukert exponent: ln(20 ÷ 1) ÷ ln(5.56 ÷ 0.45).
- UPS maker battery guidanceA recommended range of 20 to 25°C; every 8°C (15°F) rise above it halves battery life.
- Associated Press, July 14, 2019Report on the July 13, 2019 outage: about 73,000 customers on Manhattan's West Side, from Times Square to the Upper West Side, from 6:47 PM until power was restored around midnight.
Want to know what your system does in an outage?
Send us the address and a photo of the closet. We check what is on backup power, measure the load and tell you the runtime. Same-day quotes when we can. Licensed and insured.