What Is a PDU (Power Distribution Unit)? Types and Selection Criteria
A PDU (power distribution unit) distributes power from a single supply line to the servers and network devices in a cabinet through multiple outlets.
A PDU (power distribution unit) is a cabinet power strip that takes power from a single supply line and distributes it to the servers, network switches and storage devices in the cabinet through multiple outlets. It is used in data centres, server rooms and network cabinets to connect devices to a UPS output or to the mains.
Types of PDU
| Type | What it does | When to choose it |
|---|---|---|
| Basic PDU | Distributes only | Small cabinets that need no load monitoring |
| Metered PDU | Distributes and shows the total current drawn | Monitoring line overload, checking load before adding a device |
| Switched PDU | Switches individual outlets on and off remotely | Remote device restarts |
| Rack ATS (automatic transfer switch) | Selects one of two separate supplies and switches over when one fails | Redundant supply from two sources for single-corded devices |
Mounting also differs: 1U and 2U models mount horizontally and use rack height; zero U models mount vertically on the rear upright of the cabinet and use no U space.
Selection criteria
- Supply power and phases: On 230 V single phase, 16 A carries about 3.7 kW and 32 A about 7.4 kW. Ratings of 11 kW and 22 kW correspond to a 400 V three-phase supply at 16 A and 32 A. The total power of the devices in the cabinet must not exceed the PDU rating.
- Input plug: The input must match the socket in the server room. 16 A and 32 A single- or three-phase supplies use IEC 60309 (CEE) plugs; models such as the AP4421A and AP4423A have C14 or C20 inlets.
- Outlet type and number: C13 outlets are rated 10 A and C19 outlets 16 A (IEC 60320). Most servers and network devices connect to C13 with a C14-ended cord, high-power devices to C19 with a C20-ended cord. Count your devices and those to be added later.
- Redundancy: Dual-corded servers are fed from two separate PDUs. Single-corded devices need a Rack ATS for redundancy from two sources.
Common mistakes
- Treating a PDU as a UPS: A PDU distributes and measures power; it does not supply the load during an outage. Outage protection comes from an Online UPS or a Line Interactive UPS.
- Confusing metered and switched PDUs: A metered PDU cannot switch outlets off.
- Counting outlets instead of total power: Plugging a device into every outlet can overload the supply.
- Plugging both cords of a dual-corded server into the same PDU: Redundancy is lost when that PDU or its line fails.
PDU and Rack ATS models in the catalogue
All 9 active products in PDU Power Distribution Units are Schneider Electric; price and lead time are given on quotation.
| Model | Type | Mounting and supply | Outlets |
|---|---|---|---|
| EPDU2016M | Easy PDU metered | 1U, 16 A, 230 V | 8 × C13 |
| EPDU2116M | Easy PDU metered | Zero U, 16 A, 230 V, IEC 309 | 18 × C13, 3 × C19 |
| EPDU2132M | Easy PDU metered | Zero U, 32 A, 230 V, IEC 309 | 20 × C13, 4 × C19 |
| EPDU2216M | Easy PDU metered | Zero U, 11 kW, IEC 309 | 21 × C13, 3 × C19 |
| EPDU2232M | Easy PDU metered | Zero U, 22 kW, IEC 309 | 18 × C13, 6 × C19 |
| AP4421A | APC NetShelter Rack ATS | 1U, 10 A, C14 inlet | 12 × C13 |
| AP4423A | APC NetShelter Rack ATS | 1U, 16 A, 2 × C20 inlet | 8 × C13, 1 × C19 |
| AP4422A | APC NetShelter Rack ATS | 1U, 16 A, 2 × IEC 309 inlet | 1 × IEC 309 |
| AP4424A | APC NetShelter Rack ATS | 2U, 32 A, 2 × IEC 309 inlet | 16 × C13, 2 × C19 |
With its single IEC 309 outlet, the AP4422A feeds a downstream PDU rather than devices directly. Schneider Electric gives a transfer time below 10 ms for the AP4423A.
Frequently asked questions
What is the difference between a PDU and a power strip?
A PDU mounts in the cabinet and comes with server-type outlets such as C13 and C19 and an input suited to 16 A and 32 A supplies; metered models show the load. Home and office power strips are not designed for this job.
What does zero U PDU mean?
It is a PDU mounted vertically on the rear upright of the cabinet that uses no rack height, leaving the U space free for devices.
What does a Rack ATS do?
It connects to two separate supplies, for example two UPS units, and automatically transfers the load to the other when one fails. It is used to give single-corded devices a redundant supply.
Can an 11 kW PDU be connected to a single-phase line?
No. Ratings of 11 kW and 22 kW correspond to a three-phase supply at 16 A and 32 A; the input plug and the number of phases on the line must match.