turtlepokerman
Member
- Location
- USA
- Occupation
- Electrical
Can anyone give me an explanation of how duration of line to ground fault is tied to the insulation level (100%,133%, 173%) of the cable? See notes 1,2,3 in NEC 2011/2014 Table 310.104(E). I'm curious how these times were determined and if fault current has anything to do with this duration.
Reason I am asking is if I have a 5kV low-resistance grounded system with a relay that only has instantaneous (ANSI 50G element) where the INST pickup current is set to 20A, do I technically need a timer that opens the circuit after 1 hour if my cable (133% level of insulation) is operating at <20A of SLG fault current.
Any help is appreciated!
Reason I am asking is if I have a 5kV low-resistance grounded system with a relay that only has instantaneous (ANSI 50G element) where the INST pickup current is set to 20A, do I technically need a timer that opens the circuit after 1 hour if my cable (133% level of insulation) is operating at <20A of SLG fault current.
Any help is appreciated!