What is PDU?
A rack PDU takes power from a circuit and shares it among the devices in a cabinet. Racks often have two PDUs, fed from separate circuits, so that servers with dual power supplies stay up if one feed fails. The PDU has a rated input, such as a voltage, current and number of phases, and a number and type of outlets, commonly C13 and C19.
PDUs are grouped by features. A basic PDU only distributes power. A metered PDU displays the load. A monitored PDU reports load over the network. A switched PDU can also turn individual outlets on and off remotely, which can help restart a hung device without a site visit. Terms differ between makers, so check the data sheet.
A PDU is not a UPS. A UPS holds battery power to ride through an outage. A PDU only distributes power and does not store energy. In larger rooms the term PDU is also used for floor standing units that feed several racks, so say which kind you mean.
How it shows up in practice
- Check the circuit rating and the plug type before ordering, and confirm that the rack has enough capacity for the planned load. Continuous loads are usually planned below the breaker rating, so ask the site electrical team for the rule they apply.
- Use separate PDUs on separate feeds for dual power supply equipment, and balance load across them.
- Label each PDU, outlet and power cord with the feed it comes from.
- Only use qualified staff for work on live power. Replacing a PDU in a live rack needs a method and a change window.