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What is the Difference Between Central Battery System and a UPS?

There’s a growing demand in the industry for the installation of UPS (Uninterruptible Power Supplies) instead of a Central Battery Unit or static inverter, however, they are not always the best option.

While the two types of unit a quite similar, there are some essential differences to bear in mind, and in this blog, we’ll be exploring what those are, and which solution may be right for you.


UPS and CBU systems are relatively similar on the face of things, but the price of a UPS system is often significantly lower than that of a CBU – this is why a UPS system can be so appealing.

During operation, both systems offer backup power in the event of an electrical anomaly. Both utilise modules within the battery system to meet the required power rating, along with components like converters and inverters, which convert power between alternating and direct current.

Because they appear so similar, it’s easy to assume they’re interchangeable. However, there are some critical differences that you need to consider – the chief of which, is the fact that CBUs are far more resilient when fault conditions impact a building, during an emergency situation.

Why Are CBUs More Expensive?

Emergency lighting systems use fail-safe power to light the way to emergency exits during an emergency.

Explosion or fire damage to equipment connected to the grid can lead to the build-up of abnormal fault currents. Therefore, backup power supplies for emergency lighting must be able to bypass these faults to provide up to three hours of emergency lighting power.

CBUs are explicitly designed for emergency lighting installations, which means they have more energy capacity when compared to UPS systems. This means they are more resilient to overload, and it enables the CBU to operate a facility’s main switchgear to overcome high-level fault currents.

UPS’s are not designed to power main circuit breaker, and as a consequence, it may not work as required for emergency lighting purposes.

Although we’ve established that UPS systems aren’t suitable for emergency lighting, they are still incredibly useful as fail-safe power for computers and servers in a home or office setting.

Their intended purpose is to provide power to a computer or server in the event of a power cut, for long enough that the backup power can turn on, or to give the operator enough time to perform the correct shutdown procedure to prevent damage to hardware or data.

CBU Features

The components inside the CBU system include batteries, a battery charger, control circuitry, alarms and instruments. These are manufactured to provide at least three hours of emergency lighting with no more than five-second response time.

CBUs are also required to meet the legal requirements for frequent testing, to adhere to safety regulations.

Testing can involve time and resource-heavy external professionals, which is why some systems are manufactured with a built-in capability to meet the IEC 63034 standard for automatic emergency light testing.

This feature replicates a power outage and then tests the emergency lighting circuits to ensure they function as expected. It then uploads test results to the building management system to log a centralised record of the test.

What Standards and Regulations Are There for Emergency Lighting?

A selection of standards regulates emergency lighting systems in the UK. These include workplace safety, fire safety, as well as measures that control design, material, clarity, size, locations of the fittings, central power supply and maintenance.

Because CBUs are often used as central power supplies, they must meet the BS EN 50171 standard, which dictates that the equipment must be able to clear faults and provide enough power to illuminate escape routes in commercial, residential and industrial premises.

Although a UPS system can also achieve this, it must be able to handle the required power – only then is it considered fit for purpose in emergency lighting solutions.

In almost all cases, it is better to select a BS EN 50171 certified CBU, rather than dedicating additional engineering work to uprate a UPS system.

Health & Safety systems, such as emergency lighting, has very much been in the spotlight since the Grenfell Tower disaster of June 2017.

Installing the correct equipment will not only protect those inside the building during an emergency, but it will also protect those who employed to purchase, install and maintain the equipment.

If you’d like to learn more about what we’ve covered in this piece, or you’re interested in either CBU or UPS power supply systems, or any of our other products or solutions, then why not contact us today for more information?

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