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Topic review - NFPA 70E and Improved Electrical Maintenance
Author Message
  Post subject:  Re: NFPA 70E and Improved Electrical Maintenance  Reply with quote
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.
Post Posted: Wed Aug 24, 2016 6:11 pm
  Post subject:  Re: NFPA 70E and Improved Electrical Maintenance  Reply with quote
PaulEngr wrote:
... that it is labelled (again, incorrectly) "dangerous" and now they don't do maintenance on the switchgear anymore at all...


I think the software and label manufacturers have done the industry a great dis-service by continuing to use the word "Dangerous" as a level of PPE.
Personally, I like the term 'Prohibited' for >40cal/cm^2.
Post Posted: Mon Aug 22, 2016 3:40 pm
  Post subject:  Re: NFPA 70E and Improved Electrical Maintenance  Reply with quote
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.
Post Posted: Mon Aug 22, 2016 9:55 am
  Post subject:  Re: NFPA 70E and Improved Electrical Maintenance  Reply with quote
I've found that its greatly dependent upon the client. There's always some people that are ahead of the curve and have been performing regular maintenance before anyone suggested it (I'll admit, this is rare). About half the time I suggest starting a maintenance program I'll get a positive response and questions about how to start.
Post Posted: Mon Aug 22, 2016 9:25 am
  Post subject:  Re: NFPA 70E and Improved Electrical Maintenance  Reply with quote
I have several clients who have changed and now rely on Thermal Imaging and no longer perform routine maintenance on their low voltage (600v) gear.
Post Posted: Mon Aug 22, 2016 7:45 am
  Post subject:  Re: NFPA 70E and Improved Electrical Maintenance  Reply with quote
At least one client went through an arc flash study and since their main distribution bus is 23 kV, the professional engineer did the "conservative" thing and rated it according to Lee equation. Then everything was labelled some stupidly high incident energy so that it is labelled (again, incorrectly) "dangerous" and now they don't do maintenance on the switchgear anymore at all. For a while we used the tables when they were up to 35 kV but now they are back down to 15 kV, guess where we are at? Thank you, 70E.
Post Posted: Mon Aug 22, 2016 4:03 am
  Post subject:  NFPA 70E and Improved Electrical Maintenance  Reply with quote
The duration of an arc flash can be greatly affected by the condition of electrical protective devices - i.e. circuit breakers, relays etc. NFPA 70E has been placing an increased emphasis on equipment being properly maintained.

Has your company/client increased the emphasis on electrical maintenance as a result of 70E?

Yes
No
Many clients - it depends
Post Posted: Sun Aug 21, 2016 1:52 pm

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