NEMA Connector

Every power cord in North America terminates in a NEMA connector. The NEMA (National Electrical Manufacturers Association) numbering system makes it possible to identify a connector's electrical characteristics from the designation alone.

How NEMA numbering works

The designation has two parts separated by a hyphen:

Prefix — the configuration number, which encodes voltage and grounding:

• 5 = 125V, 2-pole, 3-wire grounded (standard North American single-phase)
• 6 = 250V, 2-pole, 3-wire grounded (higher-voltage single-phase)
• L5 = 125V, locking, 2-pole, 3-wire (the L means locking)
• L6 = 250V, locking, 2-pole, 3-wire

Suffix = current rating in amps: 15, 20, 30, 50, 60

So a NEMA 5-20 is a 125V, 20A, straight-blade connector. A NEMA L6-30 is a 250V, 30A, locking connector.

Common types in IT environments

NEMA 5-15 (125V / 15A) — the standard North American household outlet. Every office workstation and consumer device plugs into this.

NEMA 5-20 (125V / 20A) — one blade is T-shaped to prevent plugging a 20A device into a 15A circuit. Used on 20A branch circuits common in server rooms.

NEMA L5-20 (125V / 20A, locking) — L-series connectors twist and lock in place, preventing accidental disconnection. Standard for UPS output connections and PDU inputs in IT environments.

NEMA L5-30 (125V / 30A, locking) — higher current locking connector for larger UPS units and PDUs.

NEMA L6-20 (250V / 20A, locking) — for 240V circuits, common on dual-corded servers where you want 240V efficiency (same watts, half the current, less heat in the wiring).

NEMA L6-30 (250V / 30A, locking) — large PDUs, transfer switches, generator connections.

The locking connector (L-series) is the right choice for any connection where accidental disconnection would cause an outage. In a data center or server room, all PDU connections should use locking connectors.