UPS Systems Explained: How to Choose the Right Backup Power for Network and Industrial Equipment

Quick overview: This guide explains ups systems and the practical checks that help you understand and plan an installation. Use the contents below to go directly to the relevant section.

An uninterruptible power supply, or UPS, provides temporary backup power and power-conditioning functions to connected equipment when the normal electrical supply fails or moves outside the UPS system's permitted operating conditions.

UPS systems are widely used for network switches, routers, servers, communications equipment, PLC and SCADA infrastructure and other equipment that should remain operational long enough to ride through short interruptions or shut down in a controlled manner.

Selecting a UPS is not simply a matter of choosing the largest VA number within budget. The real load in watts, power factor, required runtime, UPS topology, battery system, input supply, output requirements and operating environment all need to be considered.

What Does a UPS Actually Do?

Depending on its design, a UPS can provide several functions:

• Temporary battery-backed power during an outage
• Protection against certain supply disturbances
• Voltage regulation
• Power conditioning
• Controlled shutdown time for connected systems
• Continuity while a standby generator starts and stabilises

The exact protection and performance depend on the UPS topology and model.

UPS vs Surge Protector

A surge protection device and a UPS are not the same thing.

A surge protector is intended to limit certain transient overvoltages. A UPS provides stored energy so compatible connected equipment can continue operating temporarily when the normal supply is interrupted.

Some UPS systems incorporate surge-protection functions, but this does not mean a UPS replaces every surge-protection requirement in an electrical installation.

UPS vs Inverter

The terms UPS and inverter are sometimes used interchangeably in casual conversation, but the products can be designed for different applications.

A UPS is typically designed around continuity and power protection for connected loads, with defined transfer behaviour, battery management and electrical characteristics.

Inverter-based backup systems can also provide stored-energy power, but their operating characteristics, transfer time, charging system, battery arrangement and intended load profile vary.

For sensitive network and control equipment, the actual electrical specifications matter more than the marketing label.

VA vs Watts

UPS ratings commonly include both volt-amperes, or VA, and watts.

Watts represent real power consumed by the load.

VA represent apparent power, which considers voltage and current without being identical to real power for many AC loads.

A UPS must satisfy both its VA limit and its watt limit.

This is why selecting a UPS from VA alone can result in an undersized system.

Why a 1000 VA UPS Is Not Automatically a 1000 W UPS

A UPS rated at 1000 VA may have a maximum real-power output lower than 1000 W, depending on the model's power factor rating.

For example, two different 1000 VA UPS models can have different watt ratings.

When comparing UPS systems, always check the manufacturer's stated output capacity in both VA and watts.

How to Calculate the Connected Load

The best starting point is to identify every device that will be connected to the UPS and determine its maximum or design power requirement.

A load list might include:

• Industrial Ethernet switch
• PoE switch
• Router or gateway
• Fibre media converter
• PLC power supply
• HMI
• SCADA workstation
• Server or NVR
• Wireless equipment
• Other essential control or communications equipment

Add the relevant loads and allow appropriate capacity for operating conditions and reasonable future expansion.

Do Not Size a UPS From the Equipment's Nameplate Current Alone Without Understanding the Load

Nameplate information can be useful, but some equipment lists maximum input values that differ substantially from normal consumption.

For existing installations, measured load data can provide useful additional information where appropriate and safely obtained.

For new systems, manufacturer power-consumption specifications and design loads should be used.

Allowing Capacity Headroom

Operating a UPS continuously at or very near its maximum rating can leave little capacity for load changes, startup conditions or future additions.

Appropriate design headroom depends on the equipment and project requirements.

Oversizing should also be sensible rather than arbitrary because UPS efficiency, battery configuration, cost and physical size can change significantly as capacity increases.

What Is UPS Runtime?

Runtime is the approximate period for which the UPS can support a specified load from stored battery energy under defined conditions.

Runtime is not determined by the UPS VA rating alone.

It depends on:

• Connected load
• Battery capacity
• Battery condition
• UPS efficiency
• Battery voltage
• Temperature
• Battery age
• Discharge characteristics

Manufacturers commonly provide runtime charts or calculators for specific models.

Runtime Falls as Load Increases

A UPS that can support a small network load for a long period may provide only a short runtime at a much heavier load.

Do not assume that a quoted runtime applies at the UPS's full rated capacity unless the specification explicitly says so.

When requesting a UPS, specify both the load and the required runtime.

What Runtime Do You Actually Need?

The correct runtime depends on the purpose of the UPS.

Some installations only need enough time to ride through brief interruptions or allow a generator to start. Others need sufficient time for controlled shutdown. Remote telemetry or communications equipment may require substantially longer autonomy.

Define the operational requirement before choosing the battery system.

Standby, Line-Interactive and Online UPS Systems

UPS systems are available in different topologies.

Standby or offline UPS systems normally supply the load from the utility source and switch to battery-backed inverter operation when required.

Line-interactive UPS systems can provide voltage regulation over a range of input conditions while retaining a battery-backed transfer arrangement.

Online double-conversion UPS systems continuously convert incoming AC to DC and then create the output AC through the inverter during normal operation, subject to the design and operating mode of the specific unit.

Each topology has appropriate applications. Online is not automatically necessary for every load, and a lower-cost topology should not automatically be assumed suitable for every critical industrial application.

Transfer Time

Some UPS topologies have a finite transfer time when changing from normal supply to battery operation.

Many modern electronic loads can tolerate the transfer time of a correctly selected UPS, but highly sensitive or specialised equipment may have stricter requirements.

Online double-conversion systems typically provide continuous inverter-supplied output in their normal double-conversion mode, avoiding the same type of transfer event to battery operation.

What Is Pure Sine Wave Output?

UPS inverter output waveforms differ between products.

Some units provide a sinusoidal output, while lower-cost products can use approximated or stepped waveforms during battery operation.

Modern power supplies, active power-factor-correction equipment and sensitive devices can have specific waveform requirements.

Where compatibility matters, confirm the UPS output waveform against the connected equipment rather than assuming every UPS output is identical.

UPS for Network Equipment

Network infrastructure is a common UPS application because a small number of devices can determine whether an entire site retains communications.

Typical protected equipment can include:

• Core switches
• Industrial Ethernet switches
• Routers
• Firewalls
• Wireless controllers
• Fibre equipment
• Media converters
• Network management systems

When calculating the load, include all equipment that must remain operational for the network path to function.

UPS for PoE Switches

A PoE switch can consume substantially more power than a similar non-PoE switch because it supplies power to connected devices.

When sizing a UPS for a PoE switch, do not use only the switch's electronics consumption. Include the expected PoE load supplied to access points or other powered devices.

The UPS may therefore need to support:

Switch consumption + PoE device load + other connected equipment.

This is a common source of undersizing.

UPS for Industrial Control and Automation Equipment

UPS systems can be used to support selected automation and control loads such as PLCs, HMIs, industrial computers, network switches, instrumentation power supplies and SCADA communications infrastructure.

Not every industrial load should be placed on the same UPS.

Motors, heaters, large contactors, solenoids and other high-inrush or high-power loads can require very different backup-power design from sensitive electronic control equipment.

The critical-load boundary should therefore be defined deliberately.

AC UPS vs DC UPS

Many industrial control systems operate internally from 24 V DC or another DC supply.

In some applications, a DC UPS or battery-buffer module can provide backup directly on the DC control supply rather than converting battery energy to AC and then back to DC through another power supply.

AC and DC UPS architectures each have advantages depending on the equipment and system design.

Softcore Group Industrial Solutions can source suitable power and backup equipment according to the specified project requirement, subject to product availability and quotation.

Battery Types

UPS systems can use different battery technologies depending on the product.

Traditional UPS systems commonly use sealed lead-acid battery arrangements. Some modern systems use lithium-ion or other battery technologies.

Battery chemistry affects cost, lifecycle, weight, charging behaviour, temperature performance and replacement requirements.

Only batteries approved or specified for the UPS system should be used.

Internal vs External Batteries

Smaller UPS systems often contain internal batteries.

Systems requiring longer runtime may support external battery packs or cabinets.

External battery capability must be confirmed for the specific UPS. A battery pack should not be added merely because the voltage appears compatible.

The UPS charger, battery configuration, protection and manufacturer requirements must all be considered.

External Battery Packs

Manufacturer-approved external battery modules can increase runtime on compatible UPS models.

When requesting extended runtime, specify the required load and autonomy rather than simply asking for additional batteries.

This allows the UPS and battery system to be sized as one solution.

Battery Runtime Changes With Age

UPS batteries are consumable components.

As batteries age, their available capacity can decline, reducing runtime even though the UPS electronics continue to operate normally.

Battery replacement intervals depend on battery technology, temperature, cycling, charging conditions and manufacturer guidance.

Temperature Has a Major Effect on Batteries

High temperature can shorten battery life significantly.

A UPS installed inside a hot outdoor cabinet or poorly ventilated equipment room may experience very different battery life from the same unit operating in a controlled environment.

Environmental temperature should therefore be considered when selecting the installation location and maintenance plan.

Battery Replacement

Some UPS systems allow batteries to be replaced by authorised or competent personnel without replacing the complete UPS.

Higher-end systems can support hot-swappable battery modules under specified procedures.

Always follow manufacturer safety instructions. UPS battery systems can deliver very high fault currents and should not be treated as ordinary small batteries.

Rack-Mount vs Tower UPS

UPS systems are available in several mechanical formats.

Rack-mount UPS systems are designed for standard equipment racks and network cabinets.

Tower UPS systems are freestanding and can be more convenient where rack space is unavailable.

Some models can operate in rack or tower orientation using suitable mounting hardware.

Confirm rack depth, rack-unit height, weight and rail-kit requirements before ordering.

UPS Weight Matters

Batteries make UPS systems heavy.

Large rack UPS units and battery packs can impose substantial loads on cabinets, shelves and floors.

Check cabinet load capacity, mounting rails and installation handling requirements, particularly for larger systems.

Input Plug and Output Socket Types

UPS systems are supplied with different input and output connection arrangements.

Depending on capacity, a UPS can use standard plugs and sockets, IEC connectors, terminal blocks or hardwired electrical connections.

Do not assume that a UPS can simply plug into the existing socket or that every connected device has a compatible output connector.

For larger systems, electrical installation may need to be performed by appropriately qualified personnel.

Single-Phase vs Three-Phase UPS

UPS systems are available for single-phase and three-phase applications.

Large systems can use three-phase input, three-phase output or other input/output arrangements depending on design.

Specify the actual electrical supply and load requirements rather than selecting a UPS only by kVA rating.

Input Voltage and Frequency

The UPS must be compatible with the available electrical supply.

Confirm nominal input voltage, frequency, permitted operating range and any generator requirements.

Output voltage and frequency requirements should also match the protected equipment.

Generator and UPS Compatibility

UPS systems are frequently used between a generator and sensitive loads.

When utility power fails, the UPS supports the load while the generator starts. Once the generator supply is stable and within the UPS's acceptable input limits, the UPS can return to normal operation and recharge its batteries.

Generator sizing and regulation matter because the UPS can present both load and battery-charging demand.

Poor frequency or voltage stability can cause a UPS to reject the generator supply and remain on battery.

Do Not Size the Generator Only for the UPS Output Load

When a generator supplies a UPS, the generator may need to support the protected load, UPS losses and battery recharge demand.

The required generator-to-UPS sizing relationship depends on UPS design, generator characteristics and manufacturer recommendations.

For larger systems, the generator and UPS should be assessed together.

Automatic Voltage Regulation

Line-interactive UPS systems commonly use automatic voltage regulation to correct certain input-voltage variations without immediately switching to battery operation.

This can reduce unnecessary battery cycling where the supply experiences moderate voltage fluctuations.

The regulation range and behaviour vary by model.

Online Double Conversion and Power Quality

An online double-conversion UPS normally supplies the load through its inverter during standard double-conversion operation.

This can provide a tightly controlled output and isolate the load from a range of input disturbances within the UPS design limits.

Efficiency, operating modes and bypass behaviour should still be reviewed for the selected model.

What Is Bypass?

A bypass path allows the load to be supplied from an alternate AC path rather than through the normal inverter power path under specified conditions.

UPS systems can include static bypass, maintenance bypass or both depending on the model and installation.

Bypass functionality is particularly important in larger or critical systems because it can allow maintenance or support the load during certain UPS conditions.

Static Bypass vs Maintenance Bypass

Static bypass is an internal or system-controlled transfer path used by the UPS under defined conditions.

Maintenance bypass provides a means of electrically bypassing the UPS so maintenance can be carried out while the load remains supplied, where the installation is designed for this purpose.

Maintenance bypass arrangements require correct electrical design and safe switching procedures.

UPS Efficiency

No UPS is perfectly efficient.

Conversion losses create heat and increase input energy consumption.

Efficiency varies with UPS topology, operating mode and load level.

For larger installations, efficiency can materially affect operating cost and cooling requirements.

Heat and Ventilation

UPS systems and batteries generate heat.

Installation spaces require suitable ventilation and environmental control according to the equipment specification.

Do not pack a UPS tightly into a cabinet without checking required clearances, airflow and operating-temperature limits.

SNMP and Network Monitoring

Many business and industrial UPS systems support optional or integrated network-management functions.

An SNMP or network management card can provide information such as:

• Input status
• Output status
• Load percentage
• Battery condition
• Estimated runtime
• Alarms
• Temperature where supported
• Event logs

Remote monitoring is particularly useful for unattended communications rooms and remote infrastructure.

USB and Serial Monitoring

Smaller UPS systems can provide USB or serial communications for local monitoring and controlled shutdown of a connected computer or server.

Check software and operating-system compatibility if automatic shutdown is required.

Dry Contacts and Relay Interfaces

Industrial or larger UPS systems can provide relay outputs or dry-contact interfaces for alarms and status signals.

These can be integrated into a PLC, BMS, SCADA or alarm system where supported.

Electrical ratings and signal logic should be confirmed before connection.

Emergency Power Off

Selected UPS systems provide an Emergency Power Off, or EPO, interface.

This is used in applications requiring a controlled means to disable UPS output under defined emergency procedures.

EPO design is safety-related and must be implemented according to manufacturer instructions and applicable site requirements.

Redundant UPS Architectures

Critical systems can use redundant UPS architectures to reduce dependence on a single power-conversion unit.

Redundancy can be implemented in different ways, including parallel UPS systems or dual power paths to equipment with redundant power supplies.

Simply installing two UPS units does not automatically create a correctly coordinated redundant system.

UPS and Dual-Power Network Equipment

Some industrial switches, servers and network appliances provide dual or redundant power inputs.

Where the equipment architecture supports it, these inputs can be supplied from appropriately independent power paths to improve resilience.

The entire upstream electrical design should be considered rather than treating the redundant input terminals alone as complete redundancy.

Can a UPS Run Motors?

Some UPS systems can support motor loads when specifically engineered for them, but motors can have high starting currents and dynamic load characteristics.

A UPS sized for electronic network equipment should not automatically be used to power pumps, fans or other motors.

Motor backup applications require proper load and starting analysis and can call for different power-system solutions.

Can a UPS Run a Laser Printer?

Laser printers can have high peak power demand when their fuser operates.

Many small UPS manufacturers advise against connecting laser printers to battery-backed outputs because the peak load can overload the UPS.

Check the printer and UPS manufacturer recommendations rather than assuming all office equipment can share the same backup outlets.

Load Shedding and UPS Systems

Frequent outages increase the number and depth of battery discharge cycles.

A UPS designed mainly for occasional short outages can experience accelerated battery wear if repeatedly used for long backup periods.

Where extended or frequent outages are expected, runtime, charging time, battery cycle life and overall backup architecture should be considered carefully.

Recharge Time

After a battery discharge, the UPS needs time to recharge.

If outages occur again before the battery has recovered, the available runtime can be lower than expected.

Recharge performance is therefore important in environments with frequent power interruptions.

UPS Maintenance

Maintenance requirements depend on the UPS size and technology.

Typical considerations include:

• Battery condition
• Battery replacement schedule
• Alarm review
• Fan condition
• Dust and ventilation
• Firmware where applicable
• Load level
• Runtime testing
• Electrical connections
• Bypass operation

Larger systems should be maintained according to manufacturer and site procedures by competent personnel.

Common UPS Selection Mistakes

• Selecting a UPS from VA rating alone
• Ignoring the watt rating
• Not specifying required runtime
• Using normal load instead of considering maximum design load
• Forgetting PoE device power when backing up a PoE switch
• Assuming every UPS has pure sine-wave output
• Ignoring transfer-time requirements
• Not checking input and output connectors
• Forgetting rack depth and weight
• Assuming external batteries can be added to any UPS
• Ignoring battery temperature and lifecycle
• Not considering recharge time during frequent outages
• Ignoring generator compatibility
• Connecting motors or high-inrush equipment without proper sizing
• Assuming a UPS replaces the site's complete surge-protection system

Replacing an Existing UPS

When replacing a UPS, provide the existing manufacturer and exact model number where possible.

Also record:

• VA and watt rating
• Current load percentage or measured load
• Required runtime
• Battery configuration
• Input voltage and connector
• Output socket or terminal requirements
• Rack or tower format
• SNMP or communications card
• External battery modules
• Generator connection
• Bypass arrangement

If the existing UPS is repeatedly overloaded or no longer provides enough runtime, a like-for-like replacement may not solve the underlying sizing problem.

A Practical Planning Checklist

For an accurate UPS quotation, provide as much of the following as possible:

• Application: ___
• Equipment to be backed up: ___
• Total load in watts: ___ W
• Total load in VA if known: ___ VA
• Required runtime: ___ minutes/hours
• UPS topology required: standby, line-interactive, online or unsure
• Input supply: ___ V / single phase / three phase
• Output requirement: ___
• Rack or tower: ___
• Rack depth if applicable: ___
• External battery capability required: yes or no
• Generator supply: yes or no
• SNMP/network monitoring required: yes or no
• USB/serial monitoring required: yes or no
• Dry contacts required: yes or no
• Maintenance bypass required: yes, no or unsure
• Operating environment: ___
• Existing UPS model if replacing: ___
• Quantity: ___

If the load is unknown, provide exact model numbers and quantities for the equipment that must remain powered. This is far more useful than requesting a UPS based only on an approximate cabinet size.

For UPS enquiries, providing the connected load in watts and required runtime is particularly important. These two values help narrow the required UPS and battery configuration before a quotation is prepared.

Technical Note

This article provides general purchasing and power-protection information. UPS sizing, electrical installation, battery systems, generator coordination, bypass arrangements, earthing, surge protection and critical-load architecture must be assessed for the specific installation. Manufacturer documentation, applicable electrical standards, site requirements and competent electrical assessment take precedence. Electrical installation and maintenance must be carried out by appropriately qualified personnel where required.

Related catalogue examples: UPS & Backup Power. For an equipment enquiry, contact Softcore Group Industrial Solutions at info@softcoregroup.co.za.