Any county, city, incorporated town or village or other political corporation or subdivision of the state, by vote of the qualified electors thereof voting thereon, may become indebted in an amount not to exceed five percent of the value of taxable tangible property therein as shown by the last completed assessment for state or county purposes, except that a school district by a vote of the qualified electors voting thereon may become indebted in an amount not to exceed fifteen percent of the value of such taxable tangible property. For elections referred to in this section the vote required shall be four-sevenths at the general municipal election day, primary or general elections and two-thirds at all other elections.