lower ratings. The standard also includes three-phase devices rated at 250 V (phase-to-neutral) / 440 V (phase-to-phase). The Swiss standard does not require the use of child protective shutters. The Swiss standard was first described in 1959. 10 A plugs and sockets (Type J) SEV 1011 defines a "Type 1x" series of 10 A plugs and sockets. The type 11 plug is unearthed, with two 4 mm diameter round pins spaced 19 mm apart. The type 12 plug adds a central 4 mm diameter round earth pin, offset by 5 mm. The type 12 socket has no recess, while the type 13 socket is recessed. Both sockets will accept type 11 and type 12 plugs, and also the 2.5 A Europlug. Earlier type 11 & 12 plugs had line and neutral pins without sleeved pins, which present a shock hazard when partially inserted into non-recessed sockets. The IEC type J designation refers to SEV 1011's type 12 plugs and type 13 sockets. Unique to Switzerland is a three-phase power socket compatible with single-phase plugs: The type 15 plug has three round pins, of the same dimensions as type 12, plus two smaller flat rectangular pins for two additional power phases. The type 15 socket is recessed, and has five openings (three round and two flat rectangular). It will accept plugs of types 11, 12, 15 and the Europlug. 16 A plugs and sockets SEV 1011 also defines a "Type 2x" series of 16 A plugs and sockets. These are the same as their 10 A "Type 1x" counterparts, but replace the round pins with 4 mm × 5 mm rectangular pins. The sockets will accept "Type 1x" plugs. The unearthed type 21 plug has two rectangular pins, with centres 19 mm apart. The type 23 plug adds a central rectangular earth pin, offset by 5 mm. The recessed type 23 socket will accept plugs of types 11, 12, 21, 23 and the Europlug. Again, the three-phase power socket is compatible with single-phase plugs, either of 10 A or 16 A ratings: The type 25 plug has three rectangular pins of the same dimensions as type 23, plus two rectangular pins of the same dimensions as type 15. The corresponding type 25 socket is recessed and will accept plugs of types 11, 12, 15, 21, 23, 25 and the Europlug. Adaptors etc. A 2012 appendix to SEV 1011:2009, SN SEV 1011:2009/A1:2012