Conductor Spacing           A very old standby Peak Voltage Between Conductors  DC or AC IPC-ML-910A With no coatings to 10,000 ft. altitude IPC-ML-910A With no coatings above 10,000 ft altitude IPC-ML-910A With soldermask or internal layers IPC-ML-910A MIL-STD-275D 0-15 .015" .25" .005" 16-30 " " .010" 31-50 " " .015" 51-100 .25" .600" .020" 101-150 " .125" .030" 151-170 .50" " " 171-250 " .250" " 251-300 " .500" " 301-500 .100" " .060" 500+ .0002" / volt .0010" / volt .00012" / volt