208V rack PDUs

208 V is the line-to-line voltage of the 120/208 V three-phase service most commercial buildings run, and it is the data-center default for one arithmetic reason: watts are volts times amps, so the same 30 A circuit that delivers about 3.6 kVA at 120 V delivers roughly 6.2 kVA at 208 V. That is nearly twice the equipment per circuit, per breaker and per length of copper, and it is why dense racks are fed at the high band almost without exception. Modern server power supplies are also marginally more efficient at the higher input voltage — the manufacturer's own efficiency table states by how much for a given model. The page is labelled 208 / 230 V rather than 208 V alone because manufacturers state 208 V, 230 V or both for what is often the same unit, and the catalog groups the high band together instead of pretending the labels are three different products.

The trap at this voltage is that the receptacles do not look any different. An IEC C13 outlet is rated to 250 V and is physically identical on a 120 V strip and a 208 V strip, and the cord plugs into both — so nothing about the connector stops someone putting a 120 V-only device on a 208 V outlet and destroying it. Almost all enterprise equipment ships with an auto-ranging power supply that accepts anything from 100 to 240 V, which is why this rarely bites in a server rack; it is appliances, older KVM gear, lab equipment and consumer-grade hardware that get damaged. Check the input range printed on each device before you plug it in. Beyond that, the usual conversation applies: match the input plug to the whip that was installed, size the nameplate amperage so your continuous load stays under 80% of it, and count the C13 and C19 receptacles against the cords you actually own.