bbaumer wrote:
We never really do maintenance on energized equipment to start with. Our maintenance is done via planned outages. The equipment is degenergized then thoroughly cleaned, bolts torqued, moving parts lubed and breakers and switches exercised.
Not sure what maintenance folks are referring too that must be done energized that is now not possible due to a warning label.
Switchgear is designed to be serviced while energized. Generally the design prevents you from being able to perform infrared thermography on the bus connections. And in the case I'm referring to all the switchgear is designed as double ended so it is at least theoretically possible to de-energize, rack it out, and do everything you are describing. But the act of racking is energized work, as is "opening and closing doors" for infrared thermography, and testing for absence of voltage. So even if you attempt to do everything de-energized, you just can't get there.
As to bolt torquing...not a good idea. First of all almost immediately (minutes) after initially torquing a fastener to specification, it relaxes due to a mixture of dislocation relaxation, embedment, and similar metallurgical effects typically losing about 20% of the torque. After that point it may continue to decline a little or some other effects occur which can actually increase torque. Thus the reason that "torque checking" (using a torque wrench to "crack on" or "crack off" the fastener) has almost no correlation with the original torque.
Second if you "retorque"...continue to tighten the same fastener without loosening, you will overstretch the bolt and cause failures. If you do the opposite and first loosen, then retorque again, this loosens the fastener because it takes more torque (due to the previously mentioned fastener relaxation mechanisms) to achieve the same amount of clamping force. So unless you ramp it up to a higher torque setting each time (and risk overtorquing) to reach the same level of clamping force, this causes loosening.