What Is a PDU (Power Distribution Unit)?
A PDU distributes electrical power to the equipment in a rack. A rack PDU takes one or more feeds and splits them across many outlets for servers, storage, and network gear.
Four Levels of Rack PDU
Basic
Reliable power distribution, no measurement.
Metered
Reports total or per-outlet current draw.
Switched
Remote on/off control of individual outlets.
Intelligent
Per-outlet metering, switching, and environmental sensors.
The Rack Power Chain
A rack PDU is the last link in a chain. Power enters the facility from the utility (backed by a generator), passes through the UPS for conditioning and ride-through, and then through floor-level distribution — a floor PDU or busway — before reaching the rack. The rack PDU takes that feed, typically one per redundant path, and splits it across outlets feeding each device's power supply unit. In dual-corded designs, every rack has an A and a B PDU on independent upstream paths, and each server's two PSUs plug into different sides so either path alone can carry the load.
Because it sits immediately upstream of the equipment, the PDU is the one place in the chain where you can see what each device actually draws. Everything above it — UPS output, floor distribution — reports aggregates. That position is what makes the PDU tier decisive for capacity planning: nameplate ratings on servers routinely overstate real consumption, so teams that plan against nameplate under-fill racks, while teams that plan against measured per-outlet load can commit capacity with confidence and still respect breaker limits and redundancy headroom.
The four PDU levels differ mainly in how much of this visibility and control they give you. The table below summarizes what each type adds and where it fits.
Basic vs Metered vs Monitored vs Switched
| Type | Measurement | Remote Control | Best For |
|---|---|---|---|
| Basic | None | None | Stable, well-understood loads where cost matters most |
| Metered | Inlet (total) load, often on a local display | None | Keeping a whole rack safely under its breaker rating |
| Monitored | Network-reported, often per outlet | None | Capacity planning, energy reporting, and alerting |
| Switched | Network-reported, usually per outlet | Remote on/off and reboot per outlet | Remote and lights-out sites, outlet-level access control |
"Intelligent" or "smart" PDUs combine monitored and switched capabilities, often adding environmental sensor ports for temperature and humidity at the rack. That telemetry is exactly what a DCIM platform consumes for power, cooling, and capacity management.
What Teams Use PDU Data For
Capacity planning from measured load
Replace nameplate assumptions with actual per-outlet draw, so racks are filled to their real limit instead of a worst-case estimate.
A/B feed headroom
On dual-fed racks, keep each feed loaded low enough that one side can carry everything if the other fails — visible only with per-feed metering.
Phase balancing
On three-phase PDUs, spread load evenly across phases to avoid tripping one leg while the others sit half empty.
Remote power-cycle
Reboot a hung server or appliance from a switched outlet instead of dispatching someone to a remote site.
Finding idle equipment
Outlets drawing steady idle power with no useful work behind them point to decommission candidates and reclaimable capacity.
Energy and PUE reporting
Rack-level IT load from PDUs is the denominator of PUE — accurate outlet data makes efficiency reporting credible.
The PDU Is Where Capacity Is Won or Lost
Rack power is a hard limit. Without per-outlet data, teams leave capacity stranded — under-filling racks out of caution — or risk tripping a breaker by overloading a circuit. Intelligent PDU telemetry turns power from a guess into a plan, especially as AI racks push circuits toward their limits.
Common Questions About PDUs
What does PDU stand for?
PDU stands for power distribution unit. In a data center context it usually means a rack PDU: a strip mounted in or beside the rack that takes one or two upstream power feeds and distributes them across many outlets for servers, storage, and network equipment.
What is the difference between a metered and a monitored PDU?
A metered PDU measures load — often shown on a local display at the unit itself, typically at the inlet. A monitored PDU reports those measurements over the network, frequently per outlet, so a monitoring or DCIM platform can collect, trend, and alert on them. In practice the terms overlap, and many vendors use them interchangeably; what matters is whether the data is per outlet and whether it is available remotely.
Where does a PDU sit in the rack power chain?
Power flows from the utility (or generator) through the UPS, then through floor-level distribution such as a floor PDU or busway, into the rack PDU, and finally into each device's power supply unit (PSU). The rack PDU is the last distribution point before the equipment itself, which is why it is the natural place to measure what each device actually draws.
Do I need a switched PDU?
Switched PDUs let you turn individual outlets on and off remotely. They earn their cost in lights-out and remote sites, where power-cycling a hung device would otherwise mean a site visit, and in environments that want to lock unused outlets off so nothing is plugged in without a change record.
Why does per-outlet metering matter for capacity planning?
Nameplate ratings overstate what most equipment really draws. Per-outlet metering replaces those worst-case assumptions with measured load, so you can see how much headroom a circuit actually has, fill racks closer to their true limit, and keep A/B feeds balanced enough that either side could carry the full load during a failure.
Can PDUs from different vendors be monitored in one tool?
Yes. Rack PDUs are network-manageable devices, and a multi-vendor monitoring platform can collect their inlet, circuit, and per-outlet readings alongside device and environmental telemetry. Sensaka DCOS does this agentlessly and correlates PDU load with rack, U-position, cooling, and energy/PUE data in one view.
Bring PDU, device, and thermal data into one view
Sensaka collects power and environmental telemetry alongside hardware health, so capacity and energy planning work from real numbers.