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Central Power Supply (CPS) version of the Master series designed to protect emergency, security and safety applications such as emergency lighting, smoke detectors, fire alarms, and sprinklers. Complies fully with EN 50171.

Delivers several hours of battery autonomy with short recharge times (up to 80% of capacity within 12 hours). Dual input as standard with optional galvanic isolation. Casing meets exacting standards of EN 60598-1.

CSS Master Series


  • Central Power Supply compliant with EN 50171 standards

  • Designed for use in emergency or safety-related applications

  • Supports continuous overloads of up to 120%

  • Long battery autonomy and fast recharge times (< 12 hours)

  • Dual input as standard

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Central Supply Systems


The CSS Master is a three-phase Central Power Supply System designed for use in a wide range of emergency and safety-related applications.

It is a reliable solution for situations including emergency lighting, fire safety and prevention (i.e. smoke extractors and fire extinguishers), lifts, safety alarms, warning systems (i.e. carbon monoxide detectors), and safety signs.

Available in a 100-600 kVA power range.


Dual Input As Standard

CSS Master incorporates dual input as standard, which enables you to carry out all the mandatory system easily and safely checks without the risk of the CSS going offline.

During inspections, the bypass line continues to support the load, so you’re protected even in the event of a failure with the main input supply.


Enhanced Battery Care

CSS Master comes with a 10-year design battery capable of long duration autonomy with quick recharge times guaranteed (up to 80% of full autonomy within 12 hours).

Sophisticated monitoring and battery care systems also maximise lifespan, deploying techniques such as deep discharge protection to reduce battery degradation.


Protection Against Battery Inversion

This ensures the safety of your staff or any service engineers carrying out maintenance on your CSS. It also prevents system damage if they have been mistakenly connected with the wrong polarity.


High Overload Capacity

CSS Master can support continuous overloads up to 120% of the system’s nominal power rating. This protection isn’t time limited. 


Various Operating Modes

Every Riello UPS CSS model supports each of the operating modes set out and described in the EN 50171 standard:

  • A) Changeover mode: the load is supplied via the CSS bypass line (always supplied output “AS”). In the event of power supply failure the internal automatic device (ATSD) transfers the load to the inverter. The battery provides power to the inverter, ensuring the required runtime.
  • B) Mode without interruption: the load is supplied constantly by the CSS inverter (always supplied output “AS”). In the event of power supply failure the battery provides power to the inverter, ensuring the required runtime with no interruptions at all.
  • C) Changeover mode with additional control switching device for control switching of the load: the equipment includes one or more switching devices (CSD), which rely on the availability of the normal power supply. On power supply failure the CSD device connects the load that up until that moment was not supplied (emergency only output “EO”).
  • D) Changeover mode with additional control switching device for partial switching of the load: part of the load is supplied without interruption whilst the remaining part is only supplied upon power supply failure thanks to the CSD device (always supplied + emergency only output “AS+EO”).