Martindale vt12 voltage tester and pd690 proving device martindale vt12 the martindale vt12 is a two pole voltage indicator amp continuity tester with automatic acdc detection up to 690v bright led indicators provide immediate display of the voltage range continuity testing is via optical and acoustic indication up to 500komegathe vt12 is ergonomically designed and durable enough for both industrial and domestic use and is constructed in accordance with the latest safety standards m