Taparia MDT-81 Multi Purpose Digital Line Tester This durable line tester is very handy and easy to carry around and very safe to use . It has proper insulation and does not possess any harm to you. By pressing the upper button, one can know the DC voltage. To know the phase line, tester is placed on the PVC insulation of wire and a flash is displayed on the screen. To know the break point, tester is placed on the outside of the PVC insulation of wire, the breakpoint is known at the place where screen stops display of the flash.