name for these connectors). The maximum voltage rating of IEC 60309 connectors is 1000 V DC or AC; the maximum current rating is 800 A; and the maximum frequency 500 Hz. Plugs are available in P+N+E (unbalanced single phase with neutral), 2P+E (balanced single phase), 3P+E (3 phase without neutral), and 3P+N+E (three phase with neutral). Current ratings available include 16 A, 32 A, 63 A, 125 A and 200 A. Voltage rating and other characteristics are represented by a colour code (in three-phase plugs the stated voltage is the phase-phase voltage, not the phase-neutral voltage). Plugs have the earth pin of a larger diameter than the others, and located in different places depending on the voltage rating, making it impossible to mate, for instance, a blue plug with a yellow socket. Since the different current ratings have different overall sizes, it is also not possible to mate different pin configurations or current ratings. For example, a 16 A 3P+E 400 V plug will not mate with a 16 A 3P+N+E 400 V socket and a 16 A P+N+E 230 V plug will not mate with a 32 A P+N+E 230 V socket. Yellow 2P+E, blue P+N+E, yellow 3P+E, red 3P+E, and red 3P+N+E are by far the most common arrangements. Blue P+N+E sockets (generally 16 A, although 32 A is becoming more common) are used as standard by British and Danish campsites and yacht marinas to provide 240 V domestic mains power to frame-tents, trailer-tents, caravans, and boats; they are also used elsewhere in Europe for the same purpose, though in some countries the local domestic plug is also widely used. Static caravans generally use the similar 32 A version because of the requirement to power electrical cooking and heating appliances. The blue P+N+E 16 A version carrying 240 V is also used in shopping malls and their peripherals to power 'temporary' stalls not incorporated within a lock-up shop, there is also use in domestic gardens within Britain to power garden equipment, barbecues, and temporary lighting. The yellow 2P+E 16 A version carrying 115 V is used extensively on the London Underground railway system to power temporary usage of heavy-duty fans; it is also frequently used by tradesmen within the UK, built into a portable transformer box that is powered from a standard 13 A 240 V mains supply, to run heavy-duty power-tools designed to operate at 115 V.