Safety dual plug structure

Claim 1

A dual plug structure being mounted in a cavity defined in an electrical device, comprising: a circuit board arranged in the cavity; a pair of first contacts and a pair of second contacts being formed on the circuit board; a primary plug pivotally retained in the cavity and movable between a first erect position where the primary plug partially project beyond the cavity and a first collapsed position where the primary plug is substantially completely received in the cavity, the primary plug comprising: a first casing defining an interior space, a pair of access openings being formed in the first casing corresponding to the second contacts; a pair of prongs extending beyond the first casing and being plugged in a first external electrical socket; a pair of first terminal members fixed in the first casing and having first ends connected to the prongs and second ends extending beyond the first casing; and a pair of raised ribs formed on the first casing and corresponding to and being engageable with the second contacts; and a secondary plug rotatably received in the interior space of the primary plug and movable between a second erect position where the secondary plug partially project beyond the first casing and a second collapsed position where the secondary plug is substantially completely received in the interior space of the primary plug, the secondary plug comprising: a second casing defining a pair of blade receiving bores, and a pair of blades received and retained in the blade receiving bore and partially extending beyond the second casing and engaging with a second external electrical socket, each blade comprising a second terminal member partially extending beyond the second casing without interfering with the first casing; whereby when the primary plug is moved to the first erect position, the first terminal members engage with the corresponding first contacts and when the primary plug is moved to the first collapsed position, the first terminal members disengage from the first contact; and whereby when the secondary plug is moved to the second erect position, the second contacts extend into the first casing through the access openings thereof for engaging with the second terminal members of the secondary plug and when the secondary plug is moved to the second collapsed position, the raised ribs engage with and prevent the second contacts from engaging with the second terminal members.