The fittings are popular in open-air conditions, as the connectors have a minimum IP44 weather-proofing rating.

The blue fittings are often used for providing weather-proofed exterior sockets for outdoor apparatus.

Series I preferred current ratings (in amps) are: 16, 32, 63, 125, 250, 400, 630 and 800, with wire gauges specified as mm2.

Series II preferred current ratings (in amps) are: 20, 30, 60, 100, 200, 300, 350, 500 and 600, with wire gauges specified as AWG and circular mil.

This is useful as disconnecting under load will cause arcing which may cause damage to both the plug and socket, and risk injury to the user.

The standard specifies an additional, different design for extra-low voltages up to 50 VAC and currents of 16 or 32 A.

One or two grooves are cut in the male plug shroud to mate with corresponding keys in the female socket.

In particular the smallest (16 A) weather-resistant variant has become especially common in camping vehicles and sockets found in RV parks and marinas throughout Europe.

[10] The so-called 'Caravan Mains Socket' has almost universally replaced a wide variety of other national 230 V domestic plugs,[11] since it is pan-European and inherently safe to standard IP44.

Not all installations distinguish the line (phase) and neutral conductors, and reverse wired sockets are not uncommon, so double pole breaking RCDs and main switches are recommended.

This is also the standard connector for lighting equipment (up to 16 A) used in the British film and television industry (often as outlets from a power splitter with a higher rated 3 phase input).

The yellow P+N+E, 4h (120°) plug is a single phase connector that is in widespread use on the British Isles for 110 V building site and fairground applications.

It is prevalent in the outdoor event lighting and audio power industry as an outdoor-safe replacement for NEMA connectors.

Since these two modes do not need three phases there is also a dark yellow-orange four-pin connector available designed for a single-phase 110–120 or 220–240 volt load.

It is best to connect the high leg adjacent to the earth pin, so that it will not be misplaced by phase-swap plugs.

Switched-socket outlets with interlocks are described in IEC 60309-4 standard and are commonly used to enhance electrical safety in industrial plants.