How do operators/maintenance know when heavy machinery is truly & completely isolated? By turning the dual pole isolator handle to the “OFF” position, is it truly isolated – even if there is an LED/Pilot light indicator installed next to the isolator? Could that indicator light be faulty?
Dirty/Faulty/High Resistance contacts can result in voltage/Back EMF across the poles & can be enough to cause an ignition hazard to personnel carrying out maintenance on the assumed isolated machine/vehicle, along with other associated hazards that fault may cause in the procedure of isolation being required.
The 24VDC solution that can be installed is the Isolation Verification Control. It is a screen that can be installed to show either “LIVE”, “OFF” or “FAULT” status on a screen – no guessing. There should always be a visual, positive status of indication on the screen. If, in the remote chance that there is no screen indication at all, maintenance must be notified to investigate the issue.
Lecky's Hunter Valley 