Resources / Implementation
Implementing static transfer switches in a 2N facility
A transfer switch protects against everything upstream of it, and nothing downstream. Implementation is mostly a question of where you put it and which two sources you give it.
Choose two independent sources
- Two utility sources that do not share a substation.
- One UPS and one utility line backed by generators.
- Two independent UPS systems, UPS A and UPS B, each able to be fed from utility or generator.
See what each layout survives
Pick a layout, then fail a UPS or a downstream panel and watch the single-corded load.
Single-cord loads
These racks have one power strip. Feed that strip from a rack-mount TwinSource switch supplied by both sources and every device in the rack behaves as if it were dual-corded. When the equipment moves, the switch moves with it.
Doubling the servers is not a cheaper route to the same result. A duplicate server doubles the rack space, the power, the feeders, the UPS capacity and the cooling, and costs far more than converting the whole rack with one switch.
Dual-cord loads
Two cords protect against the loss of one source. They do not protect against a failed power supply inside the server combined with the loss of the other source: if supply A is dead and UPS B fails, the server is down, 2N or not. For loads where that matters, feed the A strip from one switch and the B strip from a second switch, each supplied by both UPS systems through different PDUs. Either power supply or either UPS can then fail without consequence.
It also restores 2N during maintenance. The moment a PDU or panel is opened for work, a 2N site is running on N. With a switch on each cord, it is not.
Super-critical loads
Some racks carry the whole site: the communication racks that connect the data center to the outside world. Give these a third source. One cord stays on UPS A. The other is fed by a static switch whose sources are UPS B and a generator-backed utility bus. The rack then survives the loss of both UPS systems, and cascading failures of that kind have happened.
Rack mount vs wall mountInstallationTraditional data centers
Questions engineers ask
Why not one large static switch for the whole room?
It cannot see failures that happen after it, and when it fails it takes every rack with it. Large switches suit large single loads. For rows of racks, point-of-use switches protect more of the path and limit the exposure.
Do the two switches on a dual-cord rack need to be on different PDUs?
Yes. Feed switch A and switch B from different PDUs so that maintenance on one PDU, combined with the loss of the other UPS, still leaves the rack powered.
Can a static switch help with maintenance?
Yes. Moving loads to the other source on command lets you work on a bus, panel or UPS with nothing connected to it.
Put it to work
Narrow the range to your voltage, current and mounting, or send us your one-line diagram and talk to an engineer.