UPS Design & Redundancy Decrease Downtime

UPS Design & Redundancy Decrease Downtime

Get clean, uninterrupted power with modular UPS

An uninterruptible power supply delivers clean, consistent power to your critical load, regardless of the state of the incoming power source. Any power anomaly from the source is filtered through the UPS, so it is transparent to your critical load. This includes everything from a complete loss of input to the UPS to sags or spikes coming from the source. In all circumstances, the UPS will correct the anomaly and automatically provide clean, uninterrupted sinusoidal power to the critical load.


A typical single module UPS system has an MTBF (mean-time-between-failure) of about 2.6M hours using the bypass source as an alternate supply for the UPS and about 100,000 hours without factoring in the bypass. On average, the UPS will operate more than 10 years without transferring to bypass.

UPS Redundancy will minimize downtime

"N" Configuration

An "N" configuration, typical in single module UPS, where N represents the size of the critical load, has an MTBF of 2.6M hours, considering the reliability of the internal bypass. However, this is not sufficient for most critical data centers, and efforts have been made to provide a redundant UPS design to improve the reliability of the overall backup system.

"N+1" Configuration

One of the more popular UPS configurations in critical power system designs adds one more module than required to support the critical load (“N+1” UPS). In an N+1 UPS configuration, as shown below, two or more UPS systems deliver power to the critical parallel bus, which feeds the critical load. A failure in one UPS module would allow the UPS to remove itself from the critical bus, while the remaining module (or modules) supports the critical load.

"2N" Configuration

The next step in UPS redundancy utilizes two independent “N” systems to support an “A” side and a “B” side power source for the critical load. In this case, a failure of the “A” side system would typically not affect the “B” system. This would be considered a “2N” UPS system. The critical load should either be a dual-corded power supply system or would need to incorporate a static transfer switch to benefit from both the “A” source and the “B” source.

"2N+1" Configuration

Another common configuration, the “2N+1” UPS design, merges the “2N” and the “N+1” designs so that each side (“A” and “B”) has enough modules to support the load, plus one additional module per side.

Other Redundant UPS Configurations


An isolated redundant configuration involves a UPS feeding the critical load while a redundant UPS provides the bypass power to the primary UPS.

Similarly, a catcher system consists of a quantity of UPS systems feeding independent critical loads, while a redundant system provides a power path to multiple systems in the event one should fail.

Every application can be unique. How the UPS redundancy is provided, and the configuration used to achieve redundancy, depends on the specific application and the distribution system itself. In addition, each application has limitations and implications. Initial cost, space constraints, single points of failure, operating costs, and maintenance should be considered with each design.

Installing a modular Mitsubishi Electric UPS provides a path to redundancy