It’s generally a good design principle to disallow the use of computer devices in a high-availability data center environment. However, some network products or legacy servers may only have single power supplies. This “single-corded” gear will require an automatic transfer of A-B switch to protect the device. Failure to do so during the design phase may lead to power loss and resulting downtime. Here’s the secret to preventing power loss on single-corded gear.

Legacy servers with single power supplies may be performing mission critical functions today, but are destined for upgrades. Until those upgrades are completed, they’re still required to be in service. This is also true of many mid-range network devices such as firewalls, network clocks or NTP servers, and even some edge switches.

These single power supply devices can still be used with reliability by utilizing automatic transfer switches also commonly called Automatic Transfer Power Distribution Units (PDU).

These low-cost devices are typically rack mountable and occupy 1U or rack unit of space. They feature dual input cords and are able to switch from one power circuit to the other in a few micro seconds when power failure is detected on one of the input leads. This transfer time is typically well within the specification of most devices, so the blip is not seen by the load. The power fails, the load transfers and the attached devices continue operating normally.

Once power returns, everything returns to normal. The same design criteria must be observed with the automatic transfer switches as dual power supplied computer devices. Limit the loads to 80% of the breaker rating and split that 80% evenly between the two power circuits.