Size the power distribution for a GPU rack in seconds. Enter the rack load, voltage system and feed topology and get the 3-phase line current, per-feed current, and the derated PDU amp rating and count you need — with the rack PDU that fits.
A rack PDU is the last link between facility power and the servers, and it has to be sized to the current the rack actually draws — with headroom for code and redundancy. This tool turns a rack load, voltage and feed topology into the line current, per-feed current and the PDU rating and count you need.
Each step is a simple, labelled calculation so you can see exactly where the numbers come from and match them to your build.
Two choices dominate rack PDU sizing: voltage and feed topology. Higher voltage means lower current for the same power, so a 40 kW rack draws about 59 A per phase at 415V but nearly double that at 208V. Because current drives conductor and PDU size, dense AI racks increasingly standardise on 400/415V distribution to keep amperage — and copper — manageable at 40, 80 and 120 kW per rack.
Feed topology sets both current and count. A single feed carries the whole rack; dual A+B feeds split the load across two independent power paths, so each PDU carries half the current and the rack survives losing a feed or a PDU. On top of that, electrical code treats the PDU as a continuous load and caps it at 80% of its rating — so you always size to current ÷ 0.8 and round up to a standard amperage.
When the per-feed requirement exceeds a single PDU rating, you either move to a higher-rated unit or split the rack across more PDUs. Getting this right early means the rack, the branch circuits and the upstream distribution all match — and the recommended PDU links straight into our catalog.
Indicative line current per phase for common rack loads on 208V and 415V 3-phase at a 0.95 power factor. Use for planning; confirm against your exact voltage, power factor and local code.
| Rack load | 208V 3-phase | 415V 3-phase |
|---|---|---|
| 10 kW | 29.2 A | 14.6 A |
| 40 kW | 117 A | 58.6 A |
| 80 kW | 234 A | 117 A |
| 120 kW | 351 A | 176 A |
Start from the rack IT load in kW and the 3-phase voltage. Line current I = (kW × 1000) ÷ (V × √3 × power factor). If the rack has dual A+B feeds, each PDU carries half that current. Then apply the 80% continuous-load derate — required rating = current ÷ 0.8 — and round up to the next standard PDU amperage (16, 32, 48, 60, 63, 100 A).
It depends on rack density and voltage. A 40 kW rack on 415V 3-phase draws about 59 A per phase; split across dual A+B feeds that is ~29 A per PDU, and after the 80% derate you size to a 48 A PDU. The same rack on 208V draws almost double the current, so higher-density AI racks favour 400/415V distribution to keep amperage — and copper — down.
A single-feed rack needs one PDU; a dual-feed (A+B) rack needs two, one per independent power path, so the rack survives losing a feed or a PDU. If the per-feed current after derate exceeds a single PDU rating (about 60 A on the recommended unit), you split the load across additional PDUs or move to a higher-rated model.
Electrical code treats a rack PDU feeding servers as a continuous load, so it must not run above 80% of its rating on a sustained basis. Sizing to required rating = measured current ÷ 0.8 builds that headroom in, protecting the breaker from nuisance trips and leaving margin for inrush and growth. This calculator applies the 80% derate automatically.
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