can meet the standard – but a UPS can only do so if it has been uprated. Otherwise, it will not be able to deliver the required level of overload protection to operate the main switchgear and clear high-level fault currents and disruptions. As a result, UPSs may not provide power for emergency lighting if nearby grid-connected equipment has been damaged during the emergency.

ARE THERE DIFFERENT REGULATORY REQUIREMENTS? Another important difference between the two types of equipment is that CPSs are often designed to help operators to meet the regulatory requirements for fire safety testing and reporting. The IEC 62034 standard requires

Jenny Paramore, ABB’s Emergi-Lite product marketing specialist explains how specifying a UPS instead of a static inverter could put building occupants at risk


ower supplies for emergency lighting are designed to supply the lamps and

luminaires that will guide people out of buildings to safety during a fire, when mains power can be lost and smoke can cause confusion. There is a growing trend for specifying

Uninterruptible Power Supply (UPS) systems instead of the traditional static inverters, which are also known as Central Power Supplies (CPSs). UPSs are typically less expensive and can seem to offer a cost saving. However, there are important

differences that mean a UPS may not provide power in an emergency when it is needed most. Although fire is unlikely, it is essential that fire safety systems work as expected and fire safety has never been under greater scrutiny, with the public enquiry for the Grenfell Tower disaster continuing. As a result, it’s worth reviewing all elements of emergency systems in residential, commercial and industrial buildings, including their power supplies, to ensure that they are fit for purpose.

WHAT IS THE DIFFERENCE BETWEEN A CPS AND A UPS? UPS and CPS systems appear similar on the surface. In theory, both systems can

provide three hours of backup power to lamps and luminaires and both contain batteries, battery charger, control circuity, alarms and instrumentation. However, CPSs are typically more expensive. This is partly because they are rated to deliver high power to operate a facility’s main circuit breakers in an emergency event, when electrical faults may arise that need to be cleared. Unusual fault currents can build up in an emergency due to fire or explosion damage to grid-connected equipment. Therefore, it is important that the backup power supply can clear these faults and then provide three hours of power for emergency lighting. For example, ABB’s Emergi-Lite EMEX CPS delivers three and a half times the power of its output rating. In comparison, UPS systems are

typically designed to provide backup power and power conditioning services for electronic equipment in data centres and telecoms installations, where high fault currents are unlikely. Power for emergency lighting is covered by the BS EN 50171 standard. It requires that central power systems have the ability to clear faults and provide backup power to light escape routes in commercial, industrial and residential facilities. In theory, either a CPS or a UPS


regular testing of emergency lighting systems and some CPSs support this by integrating an automatic testing function. This regularly replicates a power cut and then checks whether emergency lighting circuits respond as expected. Test results can then be uploaded automatically into a building management system such as BACnet or LONWORKS. This helps building owners and

managers keep a complete centralised record. It also helps to control operating costs as manual testing of fire safety equipment can be time-consuming, disruptive and expensive. In comparison, UPSs typically require

additional engineering effort to achieve this, adding extra cost to projects.

WHAT ACTION CAN READERS TAKE TO CHECK THAT CENTRAL POWER SUPPLIES ARE FIT FOR PURPOSE? Building owners and operators need to have confidence that their fire safety systems are fit for purpose and will protect a building’s occupants. It’s therefore worth checking that central power supplies can deliver the required level of overload protection – and if not, taking steps to upgrade them. Operators of existing systems should

check the technical specifications of their central power supply system and compare it with the load requirements of switchgear and emergency lighting luminaires. Installing the right equipment will

provide peace of mind and professional protection to the electrical consultants and contractors responsible for specifying, purchasing and installing such systems.


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