Aim tti safety voltage indicator tester p240 aim tti p240 p the p240 is a hand held battery powered proving unit that provides a nominal 240v dc 2ma source intended for proving the integrity of neon type test voltage indicators p p for safety compliance voltage indicators should be checked for correct operation from this known voltage source before and after every use testing is performed by inserting the test probes of the neon tester into two recessed touch proof terminals on