Martindale voltage indicator proving device and lock out kit martindale marvipdlok138 p there is nothing is more dangerous than trusting a defective voltage indicator to test for a dead circuit safe electrical work requires the use of a voltage indicator that has been proved with a proving device before and after use the martindale vipd enables you to comply with health and safety recommendations for safe working and features the following items p p 1x pd440 proving device br 1x vi13