The major difference between an expatriate and a seconded employee (“détaché”) only concerns their status with regard to French Social Security law. Therefore this notion of status only applies to French employees.
Secondment status (http://www.ameli.fr/assures/droits-et-demarches/a-l-etranger/index.php) applies to employees who continue to contribute to the French standard scheme for social security, unemployment, pension and complementary pension. It means that the employee remains covered by the French Social Security system.
Consequently return to France is made easier. This status is recommended for short stays of less than one year.
Unlike seconded employees, expatriates (http://www.ameli.fr/assures/droits-et-demarches/a-l-etranger/index.php) do no longer contribute to the French standard Social Security scheme unless they decide to enroll with the Caisse des Français de l’Etranger (http://www.cfe.fr/index.php) to continue benefiting from the French social coverage.
The expatriation assignment has an unlimited duration.
When an employee is sent abroad, they can be employed under a local contract. In that case, they will be subject to the social security scheme of their host country and will be no longer covered by the French Social Security system.