Nobody looks this up until a rack build is half finished and a power supply will not mate with the PDU in front of it. C13 and C19 are both IEC 60320 outlets — the same family, the same standard, different current ratings — and picking the wrong mix means either a PDU full of outlets nothing plugs into, or a device that arrives with a cord end the rack cannot accept. The distinction is worth ten minutes before the order and an afternoon after it.
The short version: C13 is the smaller outlet rated at 10 A, and it is what the overwhelming majority of servers, switches, routers and appliances present. C19 is the larger outlet rated at 16 A, and it is what high-draw equipment uses — big multi-socket server power supplies, blade chassis, larger UPS units and some storage shelves. The mating inlets on the equipment are C14 and C20 respectively, which is why the cord you actually order is usually described as C13-to-C14 or C19-to-C20.
Getting the pairing right is only half the job. The other half is the PDU's own supply: total capacity, input plug type and voltage all constrain how many of each outlet you can actually load, and a PDU with plenty of free C13 sockets can still be at its limit. Count the load before counting the outlets.
At a glance
Side by side
| Factor | C13 outlet | C19 outlet |
|---|---|---|
| Current rating | 10 A | 16 A |
| Mating inlet on the equipment | C14 | C20 |
| Physical size | Smaller, three rectangular contacts | Noticeably larger; will not fit a C14 inlet |
| Typical equipment | Servers, switches, routers, firewalls, most 1U and 2U appliances | High-draw server power supplies, blade chassis, larger UPS units, some storage shelves |
| Typical share of a rack PDU | The majority of outlets on most rack PDUs | A smaller number of outlets, often grouped at one end |
| Cord you order | C13-to-C14 jumper within the rack; C13 to a wall plug outside it | C19-to-C20 jumper within the rack; C19 to a higher-rated plug outside it |
| Adapters | C13-to-C19 and C19-to-C13 adapters exist | Adapting up does not raise a device's rating — the lower-rated element still governs |
| Where it bites | Ordering a PDU that is all C13 when two devices need C19 | Ordering C19-heavy when almost nothing in the rack uses it |
Specify C13 outlets when
- The rack is servers, switches, routers, firewalls and 1U or 2U appliances — the normal case
- You are buying jumper cords to go from a rack PDU to equipment inlets marked C14
- You want the highest usable outlet count in a given PDU footprint
- You are standardising cords across a fleet and want one part number to cover most of it
Specify C19 outlets when
- The rack holds high-draw equipment — large multi-socket server power supplies, blade chassis or a rack UPS
- A device arrived with a C20 inlet, which no C13 cord can serve
- You are feeding a downstream PDU or a device whose nameplate exceeds what a 10 A path should carry
- The build is being specified now and you would rather have two spare C19 outlets than none
Bottom line
Count the equipment before you choose the PDU. Most racks are overwhelmingly C13 and a small number of C19 outlets covers the exceptions — but the exceptions are the expensive ones to get wrong, because a device with a C20 inlet simply cannot be plugged into a C13 outlet. Look at every device's inlet, not its price or its size, then pick a PDU whose outlet mix matches with a little headroom on the C19 side. And confirm the PDU's total capacity, input plug and voltage separately: free sockets are not the same as free amps, and a PDU can run out of capacity long before it runs out of outlets.
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FAQ
Common questions
- What is the difference between C13 and C14?
- They are the two halves of one connection, not two alternatives. C13 is the outlet — the socket end, found on a rack PDU or on the cord that plugs into equipment. C14 is the inlet — the pin end, found on the back of a server, switch or appliance. So a jumper cord inside a rack is described as C13-to-C14: the C13 end goes onto the equipment's C14 inlet, and the other end of the cord plugs into the PDU. C19 and C20 are the same relationship one size and rating up.
- Can I plug a C13 cord into a C19 outlet?
- Not directly — they are physically different sizes and will not mate. Adapters exist in both directions, and they have their place in a temporary or a retrofit situation, but adapting does not change any device's rating. Whichever element in the chain has the lowest rating governs the whole path, so a C13 cord fed through an adapter from a C19 outlet is still a 10 A path. Where a permanent installation needs a different outlet, the right fix is the correct cord or the correct PDU, not a stack of adapters.
- How many C19 outlets does a rack actually need?
- Usually only a few, but it depends entirely on the equipment. Count the devices with C20 inlets — typically the larger server power supplies, blade chassis, rack UPS units and some storage shelves — and specify at least that many C19 outlets with a little headroom for what gets added later. Everything else in a normal rack is C13. The common mistake is either direction: an all-C13 PDU that cannot serve the two big devices, or a C19-heavy PDU whose outlets sit empty.
- Does the outlet type tell me the voltage?
- No. C13 and C19 describe the connector and its current rating, not the supply voltage, and both are used at 120 V and at 208-240 V. Voltage is a property of the PDU's input and the circuit feeding it, which is why a rack build has to settle the input plug, the circuit rating and the voltage separately from the outlet mix. A PDU with the right outlets on the wrong circuit is still the wrong PDU, so confirm all three together.
- Why does my PDU have free outlets but no capacity left?
- Because outlets and amps are different budgets. A PDU's total capacity is set by its input circuit and its own rating, and it is entirely normal to exhaust the amps while sockets remain. Rack PDUs also often divide their outlets across internal breakers or banks, so one bank can trip while the PDU as a whole is under its limit. Size the PDU against the summed nameplate draw of what it will feed — with headroom — and treat the outlet count as a secondary constraint rather than the primary one.