NOT FOR ELECTRICAL CIRCUITS...Continuity monitor for monitoring grounds or metal to metal contact when true isolation is critical.. Not for use on live circuits or any circuit containing voltage, we specifically used this to make sure MRI shield is free of building contact while construction is going on, would detect MRI shield to ground or a/c ducts touching shield or MC cable touching shield, etc. this device would plug into an extension cord or outlet, one probe on shield the other on building ground, if they make contact an audible alarm goes off so you can clear the fault and continue working...you don't want to build the mri suite and have a ground on the shield, that wont fly with the vendors..