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What’s The Difference Between A Critical And Non-Critical Load?

Critical loads directly affect an organisation’s ability to maintain key operations and must be kept running during a mains power supply failure, for example, a data centre’s servers or life support equipment in a hospital. 

As the name suggests, non-critical (or non-essential) loads can be dropped during a power cut as they aren’t fundamental to the organisation’s operations. Printers, office lighting, and desk fans are good examples of non-essential loads. 

In modern life, many organisations are now dependent on data and voice processing systems. They’ve become such a fundamental part of the everyday infrastructure that a total or even partial failure can have catastrophic consequences.  

That’s why uninterruptible power supplies and other standby power solutions such as generators have a vital role in ensuring business continuity, providing instantaneous emergency backup to the most important electronic systems, devices and equipment when there’s a mains failure or disruption to power supplies.  

These types of load are defined as ‘Critical Loads’ – loads that directly affect the ability of an organisation to operate and must either be kept running (without any break in power) when their mains supply fails or be powered down in an orderly manner to prevent system crashes, data corruption and life-shortening hardware damage. 

For most organisations, there are two further classes of load. ‘Essential Loads’ provide secondary support services that even though they aren’t operationally critical, may still be required for health and safety reasons, such as emergency lighting. These loads must still have some form of backup but do not require uninterrupted power, so can be allowed to fail or ride through the time it takes for a generator to start. 

Finally, there are ‘Non-Essential Loads’ that an organisation can afford to lose when the mains power supply fails, for example printers, general lighting and desk fans. 


Factors To Consider When Classifying Loads As Critical Or Non-Critical

Whether a load is classified as critical or non-critical depends on its importance to the organisation in terms of: 

  • Financial penalties, lost business and impact on customer service 
  • Continuity of service provision 
  • Lost production and productivity 
  • Quality, health and safety, and environmental systems 
  • Security breaches and loss of control 
  • Organisational reputation and stakeholder confidence. 


Once critical loads have been identified, they should be prioritised by their importance and how long they need to be kept running during a mains failure.  

For some critical loads like a local file server, it may only need to be backed up to enable a safe system shutdown. Others such as medical life support systems or telecoms networks may need to be kept running for as long as possible.

This prioritisation is commonly known as load shedding. 


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