Control circuit responsive to utility voltage level

For use in connecting apparatus adapted to be powered by multiple phase electrical energy at either of two discrete voltage levels to a utility power source of unknown voltage level corresponding to one of said two discrete voltage levels, said apparatus including interconnection means adapted to be interconnected in at least two combinations for correspondingly adapting said apparatus to be powered at said two discrete voltage levels, the combination comprising

• first connection means adapted for connection to a said utility power source;
• voltage transformer means having at least two primary windings and a secondary winding;
• first control relay means having first voltage sensing means connected to said first connection means and adapted to be responsive to the voltage level of the said utility power source, first relay switch means responsive to said first voltage sensing means for connecting said at least two primary windings to said first connection means in series at one of said two voltage levels and in parallel at the other of said two voltage levels such that a control voltage is provided at said secondary winding at a preselected discrete voltage level which is independent of said unknown voltage level, and second relay switch means responsive to said first voltage sensing means;
• and
• second control relay means including second voltage sensing means connected in series with said second relay switch means across said secondary winding and third relay switch means responsive to said control voltage through said second voltage sensing means and to said unknown voltage level through said second relay switch means to so interconnect said interconnection means to said first connection means as to adapt said apparatus to be powered at a one of said two discrete voltage levels corresponding to said unknown voltage level.