Better Safe than Sorry – Central Power Supply Equipment for Emergency Lighting

Better Safe than Sorry – Central Power Supply Equipment for Emergency Lighting

ABB Emergi-Lite’s Jenny Paramore, Product Marketing Specialist spoke to Professional Electrician, about why electrical contractors and installers should be careful to select the right central power supply equipment for emergency lighting – and why specifying Central Battery Units (CBU) will ensure fail-safe power to guide people to safety.

Why are central power supplies an important part of emergency lighting systems?

Safety systems for commercial, residential and industrial buildings are in the public eye as the public inquiry into the Grenfell Tower disaster is underway. Safety systems and standards are in place to keep people safe and emergency lighting plays the role of being the fail-safe guiding light to help people escape from buildings should the worst happen. Therefore it’s vital that emergency lighting and the central power supplies that power it are properly specified.

Installing the right equipment will not just protect a building’s occupants – it will also protect the peace of mind of the electrical consultants and contractors who are responsible for specifying, purchasing and installing such systems. In spite of this, we’ve noticed a recent trend for installers to purchase Uninterruptible Power Supplies (UPS) instead of the Central Battery Units (CBUs). CBUs are also known as static inverters and have traditionally been used to power emergency lighting.

Why are contractors installing UPS systems instead of CBUs?

UPS and CBU systems both provide backup power in the case of a mains outage, therefore they can seem similar. Because UPS systems are significantly less expensive, they can appear to offer an opportunity to deliver a project for less cost. However, there are significant differences that give CBUs significantly better performance, particularly in emergency situations when it is needed most.

What are the differences between CBU and UPS units?

The biggest difference is that a CBU has significantly higher overload protection than a UPS. CBUs are designed for extreme and unusual conditions that can arise during emergency situations. For example, grid connected equipment can experience damage from fire or explosion and this can lead to high fault currents arising on the network. As a result, central power supplies for emergency lighting must be able to clear any faults and then provide power to guide people to safety when all other lighting sources have failed.

CBUs are therefore designed to be able to operate a building’s main switchgear as then provide up to three hours of fail-safe power for emergency lighting. As a result, a CBU will have a higher power rating than a comparable UPS. This gives it the ability to clear large fault currents and disruptions before providing backup power for lighting. As an example, ABB’s Emergi-Lite EMEX battery system delivers up to three and a half times the power of its output rating.

In comparison, UPSs do not have the capability to operate switchgear. Their main purpose is to provide backup power in data centres and telecoms installations. They have the role of supporting electronic loads as well as cooling systems and providing enough power to cover the period between the start of a power outage and the start-up of a backup generator. In addition, UPSs also inject and absorb power to provide a steady, high quality source of power. This ensures that sensitive computing equipment is protected from transients and overvoltages that can arise on the grid when large loads are switched off and on nearby.

However, while UPS systems protect computing networks from expensive downtime, they are not typically designed with physical emergencies in mind. Therefore, they are not normally able to provide the power for switching of main switchgear. Without this capability, UPSs may not work as expected for emergency lighting when they are needed most.

What are the standards and regulations for central power?

There are multiple standards in the UK for different aspects of emergency lighting systems. Central power supplies are governed by the BS EN 50171 standard. CBUs are designed from the outset to meet this, whereas electrical consultants and contractors must uprate a UPS to give it the right level of overload protection for the job. It is therefore simpler to select a CBU that is certified to BS EN 50171 to guarantee that the unit is fit for purpose.

Are there any other benefits of a CBU?

Many CBUs have in-built capability for automatic testing to ensure that emergency lighting circuits are operating as expected – and then log test results in a building management system. Manual testing can be expensive and time consuming so automatic testing can reduce maintenance and operating costs.

For more information about ABB’s Emergi-Lite EMEX battery system and visit:




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