Rack receptacle reference
Every common rack power receptacle with its nominal capacity and — the number most tables leave out — what you can actually load onto it. A production rack is a continuous load, so NEC 210.20(A) caps it at 80% of the breaker rating.
Identifying one from a photo
Work through it in this order — it narrows to one or two candidates fast, and every step is something you can see in a phone picture.
- 1. Curved slots or round holes? Curved, hooked slots with a threaded collar mean a NEMA twist-lock. Round pin holes with a raised keyway notch mean IEC 60309 pin-and-sleeve.
- 2. Count the contacts. Three means 2 pole, 3 wire — single phase. Four means 3 pole, 4 wire. Five means 4 pole, 5 wire — three phase with a neutral.
- 3. Read the stamp. Every device is marked with its configuration, voltage, and current on the face or body. This is the only definitive answer — the first two steps narrow the field, the marking confirms it.
- 4. Check the breaker. If the marking is worn off, the circuit it lands on tells you the amperage, and the panel tells you the voltage.
A caution worth repeating: an L5-30R and an L6-30R look nearly identical in a photo and are deliberately non-interchangeable — 125 V against 250 V. Never conclude two connectors will mate from appearance alone.
NEMA L5-20R
3 contacts · 2 pole, 3 wire
- Voltage
- 120 V
- Current
- 20 A
- Phase
- Single
- Nominal
- 2.40 kVA
- Usable at 80%
- 1.92 kVA
NEMA L5-30R
3 contacts · 2 pole, 3 wire
- Voltage
- 120 V
- Current
- 30 A
- Phase
- Single
- Nominal
- 3.60 kVA
- Usable at 80%
- 2.88 kVA
NEMA L6-20R
3 contacts · 2 pole, 3 wire
- Voltage
- 208 V
- Current
- 20 A
- Phase
- Single
- Nominal
- 4.16 kVA
- Usable at 80%
- 3.33 kVA
NEMA L6-30R
3 contacts · 2 pole, 3 wire
- Voltage
- 208 V
- Current
- 30 A
- Phase
- Single
- Nominal
- 6.24 kVA
- Usable at 80%
- 4.99 kVA
NEMA L21-20R
5 contacts · 4 pole, 5 wire
- Voltage
- 208 V
- Current
- 20 A
- Phase
- Three
- Nominal
- 7.21 kVA
- Usable at 80%
- 5.76 kVA
NEMA L21-30R
5 contacts · 4 pole, 5 wire
- Voltage
- 208 V
- Current
- 30 A
- Phase
- Three
- Nominal
- 10.81 kVA
- Usable at 80%
- 8.65 kVA
CS8365C
4 contacts · 3 pole, 4 wire
- Voltage
- 208 V
- Current
- 50 A
- Phase
- Three
- Nominal
- 18.01 kVA
- Usable at 80%
- 14.41 kVA
IEC 60309 16A
4 contacts · 3 pole, 4 wire
- Voltage
- 208 V
- Current
- 16 A
- Phase
- Three
- Nominal
- 5.76 kVA
- Usable at 80%
- 4.61 kVA
IEC 60309 30A
4 contacts · 3 pole, 4 wire
- Voltage
- 208 V
- Current
- 30 A
- Phase
- Three
- Nominal
- 10.81 kVA
- Usable at 80%
- 8.65 kVA
IEC 60309 60A
4 contacts · 3 pole, 4 wire
- Voltage
- 208 V
- Current
- 60 A
- Phase
- Three
- Nominal
- 21.62 kVA
- Usable at 80%
- 17.29 kVA
IEC 60309 100A
4 contacts · 3 pole, 4 wire
- Voltage
- 208 V
- Current
- 100 A
- Phase
- Three
- Nominal
- 36.03 kVA
- Usable at 80%
- 28.82 kVA
Device connectors — IEC 60320
The receptacles above are the wall or PDU end of the circuit. The equipment end is almost always an IEC 60320 appliance coupler — the connector molded into the back of the server, switch, or storage controller. The cord connector is the female fitting on the power cord; the equipment inlet is the male fitting built into the device.
C13 / C14
cord: C13 · inlet: C14
- Voltage
- 250 V
- Current
- 10 A
- Nominal
- 2.50 kVA
The standard rack PDU outlet, and the inlet built into nearly every 1U/2U server, switch, and storage controller power supply.
C15 / C16
cord: C15 · inlet: C16
- Voltage
- 250 V
- Current
- 10 A
- Nominal
- 2.50 kVA
Same footprint and rating as C13/C14 with a heat-resistant notch rated to 120°C, used on equipment that runs hot enough to deform a standard C13 connector.
C19 / C20
cord: C19 · inlet: C20
- Voltage
- 250 V
- Current
- 16 A
- Nominal
- 4.00 kVA
The high-capacity PDU outlet, and the inlet on blade chassis, storage arrays, and other equipment that draws more than a C13 circuit can carry.
Why the usable column matters
An L6-30R reads as a 30-amp circuit and computes to 6.24 kVA. You can load 4.99 kVA onto it. The difference is not a safety margin you can spend — it is code. Conductors and overcurrent devices must be rated for at least 125% of a continuous load, which works out to loading no higher than 80% of the rating.
A load running three hours or more is continuous, which every production rack is. This is the single most common finding in a rack power audit.
How capacity is calculated
Single phase is volts × amps ÷ 1,000. Three phase multiplies by the square root of three, so a 208 V 30 A three-phase circuit is 10.81 kVA nominal rather than 6.24. That factor is why three-phase distribution dominates above roughly 10 kW per rack.
Matching receptacles to density
An 11 kW enterprise rack at 0.95 power factor needs 11.6 kVA, which is three L6-30R circuits or two 208 V three-phase 30 A feeds. A 120 kW AI rack needs roughly eight IEC 60309 60 A three-phase circuits — which is the point at which busway replaces individual whips.