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ekstra   ara
 Post subject: Arc Flash & Cable, Cable Entry Questions
PostPosted: Thu Jan 20, 2011 7:36 am 

Joined: Wed Nov 24, 2010 2:11 am
Posts: 10
Location: Maine
References I am using:
a) NFPA 70E, 2009 Edition
b) IEEE STD 1584-2002 Arc-Flash Hazard Calculations
c) IEEE STD C37.20.7-2007 Arc Fault Rated Switchgear Rated =< 38kV
d) IEEE STD C37.20.2-1999(R2005) Metal-Clad Switchgear
e) Attached diagram

From my reading of references a-d, I could not find any reference to a fault at an arbitrary point along a cable run outside of any connected equipment. All of the calculations and such appear to only deal with the equipment at either end of the cable with the cable only entering in the calculations for available fault current at the fault point.

My arc fault related questions – in your experience …
  1. How are cables handled (or are they) during an Arc Flash Hazard Analysis. I assume since the cables are insulated (i.e. not exposed) and are not normally interacted with during operation that an Arc Flash Hazard does not typically exist.
  2. Assuming proper maintenance and construction of the cable and break-out boot. Does it make a difference if the individual conductors are broken-out inside or outside the equipment?
  3. Does using a break-out boot adversely affect the cable integrity such that it is something that you worry about? My gut feeling is no, or else they would not get used.
  4. An accessible cable vault is below non-arc fault rated metal-clad switchgear. Are there any special arc fault related concerns that should be looked at and addressed?
  5. Does it matter if the cableway is enclosed or not?
  6. Can a relatively reliable prediction be made concerning the resulting cable condition during the fault event?
  7. How many failures have you experienced related to break-out components?
General cable related questions …
  1. What specific role does the cable shield play any role during a short circuit event?
  2. Does any useful (to the protection scheme) current get impressed on the shield that aids in tripping protective devices? I assume not for fuses but how about protection relays?

Thanks in advance for any information you can provide. I am particularly interested in any other documents that you feel are relevant.


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PostPosted: Fri Jan 21, 2011 5:52 am 
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Joined: Mon Mar 29, 2010 5:02 am
Posts: 136
The breakout boot installed within the equipment would provide greater mechanical protection for your conductors.. Should the boot be installed improperly or the wrong size, moisture may get into the cable assembly and lead to a cable failure.

Typically cables installed in a tray or wireway assembly are not (to my knowledge) listed separately for Arc Flash labels, or calculations.. The probability of specific cable failure is low....

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