To dispense with changing the wirings and parts of a circuit part side irrespective of the power specifications by making only the part of relay terminal blocks and connectors responsible fort the conversion of power specifications.

A relay terminal block TA2 consisting of relay terminals 'S1' to 'S5' and 'GROUND' is fixed to the apparatus side of an external terminal block TA1, comprising power terminals 'T1' to 'T3', 'N' and 'GROUND'. In addition, three short-circuiting connectors 31, 32, 33 of identical structure are mounted at the downstream side as connectors for converting power specifications. It is preset so that the short-circuiting connector 31 is used for single-phase two-wire system, the short-circuiting connector 32 for three-phase three-wire system, and the short-circuiting connector 33 for three-phase four-wire system. These short-circuiting connectors 31, 32, 33 have identical structure, with six jacks numbered from '1' to '6' being formed in the connectors with each jack being isolated electrically.