Monitoring of electrical insulation integrity

A system for monitoring the integrity of at least two layers of insulation forming part of an electrical device which further includes at least two conductive members having a potential therebetween and surrounded successively by the two layers of insulation, said system comprising:

• means defining a conductive, integrity monitoring layer interposed between said two layers of insulation such that a first one of said layers of insulation is disposed between the conductive members and said conductive layer and a second one of said layers of insulation is disposed between said conductive layer and the environment surrounding the device;
• a first impedance monitoring circuit connected between the conductive members and said conductive layer for monitoring the current passing through said first insulating layer under the influence of the potentials on said conductive members;
• and a second impedance monitoring circuit connected between said conductive layer and the environment surrounding the device for monitoring the current through said second insulating layer.