Electrical devices used in telecommunications, data centres, and healthcare require a constant and stable source of electricity.

A power supply failure – an interruption in the mains supply, frequency deviation, or a dip in voltage – can cause critical operational issues in sensitive equipment, a problem that is both expensive and can impact thousands of users reliant on the devices.

A redundant power supply is the electrical infrastructure used to safeguard 24/7 electrical equipment in industries like data centres, healthcare, and telecommunications. 

How Does Redundant Power Supply Work?

A redundant power supply combines two separate sources of electrical supply. A primary source, and a backup that will automatically take over when the primary supply fails. 

This infrastructure allows connected devices to remain in operation with no (or minimal) disruption to power supply. 

Here’s how redundant power supply works in detail:

During normal operation, the primary supply feeds the equipment load while the backup supply is available either shared or on standby. When the mains supply fails, or there is equipment failure within the primary supply, and the mains voltage dips, the backup supply switches automatically within the necessary timescale to ensure downstream equipment is not affected by any gap. 

Redundant power supply is critical where power issues that interrupt operations would be detrimental. For example, servers at a data centre are likely to crash without power resulting in data loss and service interruptions, and hospitals rely on equipment like life support devices that require a constant source of electricity.

Redundant Power Supply Configurations

Redundant power supply setups are configured in N+1, 2N or 2N+1, where "N" is the exact amount of power capacity needed by equipment.

Configuration	What It Means	Risk Level	Target Environments
N+1	Baseline capacity plus one single spare component. If any single power module fails, the spare (+1) provides the required power supply.	Low-to-Medium: Vulnerable if the second unit fails before the first is replaced, or if the entire main power supply fails.	Standard enterprise servers, network closets, and data centres.
2N	Two completely independent, mirrored systems (an A-feed and a B-feed). Each path is independently capable of carrying 100% of the total load.	Very Low: Provides two paths, avoiding a single point of failure and allowing full system maintenance without downtime.	Financial networks, and data centres.
2N+1	Two independent, mirrored systems (2N), where each side also includes its own "+1" internal spare unit.	Extremely Low: Safely protects the system even if an entire power supply fails and a module fails on the remaining active supply.	Hospitals, and mission-critical environments such as government facilities.

       

All configurations for redundant power supply must be installed in compliance with AS/NZS 3000:2018 (Wiring Rules) in Australia.

Types of Redundant Power Supply Switches 

There are two types of technology for redundant power supply switches - Static Transfer Switches (STS) and Automatic Transfer Switches (ATS). 

Static Transfer Switches use solid-state electronics to manage the transfer between sources of power supply - an STS can achieve a transfer time under 10 milliseconds, making it ideal for use with server equipment in data centres.   

Automatic Transfer Switches have a slightly longer transfer time between 30 and 100+ milliseconds. This increased duration is negligible for general infrastructure like cooling systems and lighting, but not for equipment storing or transmitting data, like those in server racks. Transfer times above 10 milliseconds can cause servers to go offline and undergo a reboot. 

Redundant Power Supply and Dual Supply PDUs

Achieving redundant power supply in data centres requires the use of dual supply PDUs (Power Distribution Unit). 

Dual supply PDUs can host two independent power inputs, both connecting through two different power supply sources, commonly referred to as an A feed and B feed.

These feeds are routed separately and independent to the rack itself. The tripping of a circuit breaker or equipment failure in one feed will have no impact on the other feed allowing the equipment to receive uninterrupted power supply.

Each power supply feed will be capable of managing the full electrical load of connected equipment.

It is also safer and easier to perform maintenance on electrical systems when using a redundant power supply, as there is a secondary supply powering sensitive equipment while repairs or maintenance work are carried out on the other supply. 

RackLink manufactures and supplies custom dual supply PDUs with options for multiple power inputs, colour-coded primary and secondary supply circuits for easy identification, and Static Transfer Switch functionality. We can design dual supply PDUs in line with your site’s requirements to maximise operational uptime.