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| NFPA 70E Table 130.7(C)(9) Question https://brainfiller.com/arcflashforum/viewtopic.php?f=2&t=1634 |
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| Author: | WBurtt [ Fri Mar 25, 2011 5:11 am ] |
| Post subject: | NFPA 70E Table 130.7(C)(9) Question |
Gentlemen; Question concerning a task as listed out in NFPA 70E Table 130.7(C)(9) that shows up in several sections for voltages =<600V "Work on energized electrical conductors and circuit parts of utilization equipment fed directly by a branch circuit of the panelboard" Is this referring to connecting/disconnecting live cables? or is this just referring to voltage and other measurements? Thanks |
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| Author: | Zog [ Fri Mar 25, 2011 7:25 am ] |
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I cannot imagine how you can justify ever disconnecting or connecting live cables? I recommend you read article 130.1 Justification for work. |
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| Author: | jghrist [ Fri Mar 25, 2011 10:23 am ] |
| Post subject: | |
WBurtt wrote: Gentlemen;
Question concerning a task as listed out in NFPA 70E Table 130.7(C)(9) that shows up in several sections for voltages =<600V "Work on energized electrical conductors and circuit parts of utilization equipment fed directly by a branch circuit of the panelboard" Is this referring to connecting/disconnecting live cables? or is this just referring to voltage and other measurements? Thanks I believe it means doing work on energized conductors or circuit parts at the equipment being served by the branch circuit. For example, measuring voltage. |
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| Author: | TheArk [ Fri Apr 08, 2011 3:22 pm ] |
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For 600v class motor control centers this entry in the table (Utilization equipment) is defined as cat#2. I work in a paper mill with 373 motor control centers. We have been wrestling for the passt year how to deal with all of the local disconnects and/or panels that are fed from these motor control centers. We have pretty much come to a conclusion that we would make a blanket statement that all of this field mounted equipment is to be treated as cat#2 devices (per the table). We would then pursue identification and labeling of circuits that potentially fall outside of that status, i.e.; extremely long circuit conductors or isolation transformer installations, etc. |
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| Author: | jghrist [ Sat Apr 09, 2011 6:42 pm ] |
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TheArk wrote: We would then pursue identification and labeling of circuits that potentially fall outside of that status, i.e.; extremely long circuit conductors or isolation transformer installations, etc.
Equipment on long circuit conductors may well have higher incident energy levels that at the MCC. If the fault current drops below a short time or instantaneous pickup value, the clearing time could increase significantly and may exceed the table assumptions. |
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| Author: | TheArk [ Sun Apr 10, 2011 1:54 pm ] |
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All of our 373 MCC's have fuses in them. We did a sensitivity study, increasing cable lengths, to prove at what circuit lengths we would exceed a Cat#2 at the recieving end. The circuit lengths where that occurs varies with the size of the cable. For MCC's with molded case circuit breakers it is alot trickier, however, to come up with a rule of thumb to follow. |
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