Where should I start to diagnose intermittent grounding on a circuit? I have 3 power strips on the same circuit with lights to indicate "grounded" and "protected". The "protected" indicator light is always illuminated, but the "grounded" indicator light is intermittent (indicator light goes from bright to very dim) About 4 hours on and then goes very dim, then back on again very bright, then dim. About 4 hour intervals. This happens on all 3 outlet strips simultaneously.