Field calculator
Rack and PDU current (amps) and 80% sizing calculator
Data center IT load runs continuously, so the current draw and the circuit that feeds it are two different numbers. This calculator converts a rack or PDU load in kilowatts to running amps, using three-phase amps = kW x 1000 / (sqrt3 x V x PF) or single-phase amps = kW x 1000 / (V x PF), then applies the NEC continuous-load rule. Enter the load in kW, the voltage (commonly 208 V or 415/400 V three-phase in the white space), the phase, and the power factor (modern server power supplies run near 1.0). Because the load is on for three hours or more, the NEC treats it as continuous and limits it to 80 percent of the branch-circuit or feeder rating, so the conductor and overcurrent device are sized for at least the draw divided by 0.8. Remember redundancy: A and B feeds each have to carry the full rack when the other path drops, so size each feed for the whole load and run each near half its rating in normal operation. Confirm the voltage, power factor, conductor derating, and overcurrent selection with the electrical engineer and the NEC.
Result
Rack / PDU current: three-phase amps = kW × 1000 / (√3 × V × PF), single-phase amps = kW × 1000 / (V × PF). Enter the rack or PDU load in kilowatts, the voltage (commonly 208 V or 415/400 V three-phase in the white space), the phase, and the power factor (modern IT power supplies run near 1.0). The tool returns the running current and the continuous-load size: because data center IT load runs three hours or more, the NEC treats it as continuous and caps it at 80% of the branch-circuit or feeder rating, so the conductor and breaker are sized for at least the draw divided by 0.8. Remember that A and B feeds are redundant: each has to carry the entire rack when the other path drops, so size each feed for the full load and run each under roughly half its rating in normal operation. This is a planning estimate; confirm the voltage, power factor, conductor derating, and overcurrent selection with the electrical engineer and the NEC.
anvilfield.com/calculators/rack-pdu-current-sizing-calculator · Free field calculators and FieldOS. A planning estimate, verify against the code, the manufacturer, and the engineer of record.
More Datacenter calculators
Rack current & sizing FAQ
What is a rack PDU?
A rack PDU is the power strip inside a server cabinet that takes one branch circuit from the floor PDU, RPP, or busway and splits it into outlets for the servers' power supplies. It is the last step in the power chain before the IT load, and it comes in basic, metered, switched, and intelligent versions.
What is the difference between a metered and a switched PDU?
A metered PDU shows the current it carries, at the inlet or per outlet, so you can track capacity against the breaker. A switched PDU adds remote on and off control of each outlet, so you can reboot a hung server or lock an unused outlet from the network. Switched strips usually meter too.
What is the difference between a rack PDU and a floor PDU?
A rack PDU is the strip inside the cabinet that feeds the servers' cords. A floor PDU is the floor-standing cabinet that takes UPS power, steps it through a transformer, and distributes it to the rows. The floor PDU feeds the rack PDU, which feeds the gear. Same three letters, two different devices.
What is a 0U PDU?
A 0U PDU is a rack PDU mounted vertically in the cabinet's rear channel, taking no rack-unit space from the 19 in mounting field. Zero U means it does not cost you a slot a server could use. Vertical 0U strips carry 30 to 40-plus outlets up the rack and suit server cabinets with a rear channel.
How many outlets does a rack PDU need?
Count outlets against the gear and the redundancy, not the rack slots. A 42U rack of dual-corded 1U servers can need 40-plus outlets per side, split across an A strip and a B strip. Add up every cord plus spares, then pick a strip with enough C13 and C19 in the right mix.