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NEMA plugs and receptacles (North America)
NEMA names follow a pattern: an optional L for locking (twist-lock), a number for the voltage and wiring configuration (5 = 125 V with ground, 6 = 250 V with ground), then the current rating, then P for plug or R for receptacle.
| Configuration | Volts | Amps | Watts at 80% continuous | Typical UPS use |
|---|---|---|---|---|
| 5-15 (standard household) | 125 | 15 | 1,440 | Input on most UPS units up to about 1500 VA; output outlets on almost all |
| 5-20 (T-slot) | 125 | 20 | 1,920 | Input on many 2000 to 2200 VA units; a 5-20R accepts 5-15P plugs too |
| L5-20 (locking) | 125 | 20 | 1,920 | Rack units in server rooms where accidental unplugging matters |
| L5-30 (locking) | 125 | 30 | 2,880 | Input on 120 V units around 3000 VA |
| L6-20 (locking) | 250 | 20 | 3,840 (at 240 V) | 208/240 V rack units |
| L6-30 (locking) | 250 | 30 | 5,760 (at 240 V) | 208/240 V units from about 3 kVA to 6 kVA |
IEC 60320 connectors (equipment and rack)
IEC connectors are common on servers, network gear and rack UPS outlets. Odd numbers are the female (cord) end; the even number above it is the matching male inlet. The current ratings listed are the international ratings; North American UL listings for cords are often higher.
| Pair | International rating | Where you see it |
|---|---|---|
| C5 / C6 ("cloverleaf") | 2.5 A | Laptop power bricks |
| C7 / C8 ("figure 8") | 2.5 A | Consoles, small electronics (unearthed) |
| C13 / C14 | 10 A | PCs, monitors, servers, switches; most rack UPS outlets |
| C19 / C20 | 16 A | High-power servers, PDUs, UPS inputs on larger rack units |
The circuit is often the hidden limit
A 1500 VA / 1350 W UPS on a 15 A circuit already uses most of that circuit's continuous capacity, and after an outage it draws extra current to recharge. If a space heater or vacuum shares the circuit, the breaker can trip with the UPS fully loaded. Put larger UPS units on their own circuit.
Quick circuit math
Add UPS losses (a few percent for line-interactive, up to about 10% for online) and recharge current on top of your load. The VA to watts converter shows the current for a given load.
Adapters and new circuits
Never modify a plug or use an adapter to fit a higher-rated plug into a lower-rated receptacle. New 20 A, 30 A or 240 V circuits must be installed by a licensed electrician under local code. See hardwired vs plug-in UPS.
Frequently asked questions
Can I plug a UPS with a NEMA 5-20P plug into a normal outlet?
No. The 5-20P has one blade turned sideways and only fits a 5-20R receptacle, which is on a 20 A circuit. Using an adapter to fit a 15 A outlet defeats the protection the plug design provides. Have a 20 A circuit and receptacle installed.
What is the difference between C13 and C19?
Both are IEC 60320 connectors used on servers and rack equipment. C13 is the common computer-style connector rated 10 A internationally (often 15 A under UL in North America). C19 is larger and rated 16 A internationally (often 20 A under UL), for high-draw servers and PDUs.
How much load can I put on a 15 A circuit?
A 15 A, 120 V circuit carries 1,800 W at its rating, but continuous loads (three hours or more) should stay at or below 80%, about 1,440 W. A UPS also draws extra input current to recharge its battery after an outage, so leave margin.
Does a twist-lock UPS plug need an electrician?
Yes, in practice. Locking receptacles such as L5-30R or L6-30R require a dedicated circuit of the right rating, installed to code. That is work for a licensed electrician.
Sources and further reading
- NEMA WD 6, Wiring Devices: Dimensional Specifications
- IEC 60320-1, Appliance couplers for household and similar general purposes
- NFPA 70, National Electrical Code (continuous load rules)