How to Size a UPS for CCTV, Access Control and Security Systems
Essential Security Supplies
A UPS should be selected from the load and required runtime, not from the VA number on the front panel. CCTV, access control, intercoms, networking, and recording equipment can all be affected differently by a power interruption, so the first step is to define which services must remain available and for how long.
For New Zealand security installers and integrators, a useful UPS design considers watts, VA, start-up demand, PoE load, topology, battery runtime, future expansion, and the operating environment. The goal is a documented load profile that can be tested at commissioning.
Define what the UPS must achieve
Before choosing a model, write down the operating objective.
- Ride through short outages: keep the system online through brief interruptions.
- Maintain selected security functions: keep critical cameras, networking, access control, or communications operating for an agreed period.
- Support an orderly shutdown: give an NVR, server, or other managed device time to shut down correctly.
- Improve power quality: use the topology appropriate to sensitive equipment or an unstable supply.
"Provide backup power" is too vague. "Maintain the NVR, PoE switch, router, and access controller for at least the agreed runtime" gives the installer and client a result that can be measured.
Build a complete load schedule
List every device connected to the battery-backed outlets and record its maximum or credible worst-case input. Use current manufacturer data or measured load where appropriate.
| Load | What to include | Common mistake |
|---|---|---|
| NVR or server | Maximum input and shutdown requirements | Using only the idle reading |
| PoE switch | Switch consumption plus powered devices | Counting the switch but not the PoE load |
| Cameras | Night-time draw, IR, heaters, accessories | Using daytime power only |
| Access control | Controllers, readers, lock supplies, network devices | Ignoring lock or charger current |
| Intercom and network | Door stations, monitors, router, ONT, converters | Backing up one device but not its network path |
If a device already has its own battery-backed supply, decide whether the UPS is supporting that charger, adding another layer of resilience, or should be excluded. A simple single-line diagram helps prevent double counting.
Understand watts and VA
A UPS normally has both a VA rating and a watt rating. The connected load must remain within both. VA represents apparent power, while watts represent real power consumed by the equipment.
For example, an NVR at 35 W, networking at 20 W, an access controller and auxiliaries at 30 W, and a PoE switch delivering 90 W total 175 W before design allowance. The final design figure should include a documented allowance for uncertainty, expected growth, and credible peak conditions.
Do not apply one fixed spare-capacity percentage to every site. A stable rack with no planned additions is different from a system where cameras, readers, or wireless links are likely to be added later.
Capacity and runtime are different
Capacity tells you whether the UPS can carry the load. Runtime tells you how long it can carry that load on battery. A larger VA number does not automatically guarantee the runtime you need.
PowerShield's current UPS sizing guide asks for a load profile in watts or VA, the operating environment, preferred case style, and desired battery time. PowerShield also warns that its calculations are a guide and that high inrush currents or unusual site conditions require additional review.
Agree the runtime target before selecting the model. Ten minutes for orderly shutdown is a different project from one hour of continued operation.
Choose the topology to suit the risk
Line-interactive and true online double-conversion UPSs behave differently during supply disturbances.
- Line-interactive: often suitable for smaller racks, networking, recorders, and general security equipment where supply conditions are reasonably stable.
- True online double conversion: continuously supplies the load through the inverter and provides zero transfer time to battery, making it suitable for critical or sensitive equipment and difficult power environments.
The topology should follow the project risk, connected equipment, and manufacturer guidance rather than habit.
PowerShield Defender Rackmount 800VA
The PowerShield Defender Rackmount 800VA UPS is currently active in the Essential Security Supplies range. PowerShield's current product information lists 800 VA / 480 W capacity, line-interactive topology, simulated sine-wave battery output, one 12 V 9 Ah battery, six Australian sockets, and two 10 A IEC outlets.
PowerShield's current brochure states approximately eight minutes of backup at 50 percent load. Treat that figure as a reference point only. Actual runtime depends on battery condition, connected load, temperature, and the exact installation.
PowerShield Commander Tower
The PowerShield Commander Tower range is currently active. PowerShield documentation lists 1100 VA / 990 W and 2000 VA / 1800 W models with line-interactive topology and pure sine-wave battery output.
PowerShield Centurion Tower
The PowerShield Centurion Tower range is currently active. PowerShield's current range page lists 1000 VA, 2000 VA, 3000 VA, 6000 VA, and 10 kVA single-phase models and describes the range as expandable with compatible battery modules for longer runtime.
Allow for PoE, inrush, and changing loads
Security loads are not always steady. IR illuminators may switch on after dark. Heated housings can add load in cold conditions. A PoE switch may run well below budget at commissioning and approach its limit after future cameras are added. Servers, displays, power supplies, and some door hardware can also produce short start-up or switching demands.
Design from the worst credible operating state, not the lowest reading seen during setup. If the manufacturer flags high inrush or a special load type, use its selection guidance or seek engineering review.
Back up the complete service path
Keeping one device alive does not keep the service alive if another required component loses power. Remote CCTV may depend on the NVR, PoE switch, router, and fibre ONT. An IP intercom may depend on the door station, switch, controller, lock supply, and receiving endpoint.
Map the complete path for each service the client expects to retain during an outage. Then decide which parts need UPS power and which already have a separate battery-backed supply.
Installation and commissioning checklist
- Confirm the final load in watts and VA where available.
- Check the load against both UPS limits with the documented design allowance.
- Verify that the topology and output waveform suit the connected equipment.
- Confirm ventilation, ambient temperature, mounting, and service access.
- Configure communications and orderly shutdown where required.
- Simulate a mains failure and confirm the intended services remain available.
- Record measured load, estimated runtime, battery date, model, and serial number.
- Document who is responsible for battery testing and replacement.
Frequently asked questions
Can I size a UPS from VA alone?
No. Check both the VA limit and the watt limit. The connected load must remain within both.
How much spare capacity should I allow?
There is no single percentage that suits every project. Allow for measurement uncertainty, expected expansion, ageing, and credible peak conditions, and document the reason for the chosen margin.
Does a bigger VA rating always mean longer runtime?
No. Runtime depends on battery configuration, efficiency, battery condition, and connected load. Use current manufacturer runtime data for the exact model and load.
When should I consider true online double conversion?
Consider it for critical or sensitive equipment, poor power quality, demanding environments, or where the project specification requires continuous power conditioning and zero transfer time.
Size from a measured load, not a guess
The right UPS is the one that supports the complete required service, remains within both its watt and VA limits, provides the agreed runtime, and can be maintained throughout its life.
Browse the UPS collection, or contact Essential Security Supplies with the connected equipment list and required backup time.
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