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ITGlossary · UPS technology
Redundant Power Supply
A second power supply inside a server or switch that takes over without interruption if the first one fails or loses its feed.
Technical level:Intermediate
Many servers, switches and storage systems have two or more power supplies, each able to power the device on its own. If one supply fails or loses its input, the other takes over without interruption, and the faulty unit can usually be replaced while the system is running (hot-swap).
The benefit is fully realised only if the supplies are connected to different sources, for example to two UPS units or to two PDUs fed from independent circuits. For devices with a single power supply, automatic transfer switches (ATS) provide similar protection.
A common mistake is plugging both power supplies into the same power strip or the same UPS, so that a single fault there takes both down.
Related terms
- Cold Start FunctionA feature that allows a UPS to be started directly from the battery without utility power.
- InverterThe component inside a UPS that converts DC power from batteries back to usable AC power.
- Line Interactive UPSA UPS that corrects voltage sags and swells with an automatic voltage regulator and switches to battery only when the voltage is lost or out of range.
- Maintenance BypassA manual switch used to isolate the UPS for servicing while still supplying power to the load.
- Offline (Standby) UPSA UPS that leaves the load on the mains and switches to battery only when the mains fails, with a short transfer time; the simplest and cheapest topology.
- RedundancyHaving more UPS units or modules than the load needs, typically in an N+1 or 2N configuration, so the load stays powered if one fails.