Frequency converter module , comprising at least one frequency converter for converting a mains frequency into a higher frequency; and comprising a base and a cover , between which the at least one frequency converter is arranged; wherein the frequency converter comprises a converter receptacle , in which a circuit board is encapsulated in an air-tight manner, for transforming an electrical current applied to the circuit board with regard to its frequency, its voltage and/or its number of phases and for outputting the transformed electrical current; the frequency converter has a housing for accommodating the converter receptacle ; the housing is configured such that it can be connected in a form-fitting manner to a housing of a similarly constructed further frequency converter ; the housing of the at least one frequency converter is configured such that a further similarly constructed frequency converter can be connected in a form-fitting manner to the at least one frequency converter on the upper side or the lower side thereof, that the base can be connected in a form-fitting manner to the at least one frequency converter at the lower side thereof and that the cover can be connected in a form-fitting manner to the at least one frequency converter at the upper side thereof; the frequency converter module is portable; the housing has a cooling apparatus for cooling the circuit board , wherein the cooling apparatus has at least one fan which is suitable for guiding air from an air inlet of the housing via an air duct , which leads along the converter receptacle, to an air outlet of the housing ; and wherein the air duct is inclined in two ways such that liquid which has passed into the air duct runs off to the air inlet and to the air outlet in an operating position of the frequency converter . at least one frequency converter for converting a mains frequency into a higher frequency; and comprising a base and a cover , between which the at least one frequency converter is arranged; wherein the frequency converter comprises a converter receptacle , in which a circuit board is encapsulated in an air-tight manner, for transforming an electrical current applied to the circuit board with regard to its frequency, its voltage and/or its number of phases and for outputting the transformed electrical current; the frequency converter has a housing for accommodating the converter receptacle ; the housing is configured such that it can be connected in a form-fitting manner to a housing of a similarly constructed further frequency converter ; the housing of the at least one frequency converter is configured such that a further similarly constructed frequency converter can be connected in a form-fitting manner to the at least one frequency converter on the upper side or the lower side thereof, that the base can be connected in a form-fitting manner to the at least one frequency converter at the lower side thereof and that the cover can be connected in a form-fitting manner to the at least one frequency converter at the upper side thereof; the frequency converter module is portable; the housing has a cooling apparatus for cooling the circuit board , wherein the cooling apparatus has at least one fan which is suitable for guiding air from an air inlet of the housing via an air duct , which leads along the converter receptacle, to an air outlet of the housing ; and wherein the air duct is inclined in two ways such that liquid which has passed into the air duct runs off to the air inlet and to the air outlet in an operating position of the frequency converter . <EOS>