NFPA-70E Table 130.7.c.a question
NFPA-70E Table 130.7.c.a question
(OP)
Ok, I am fairly new to the arc flash issue so I am hoping to get some assistance from the more experienced engineers out there.
In the table notes, it mentioned clearing times of 0.03sec (2-cycles). What devices clear in 2-cycles (other than fuses)? Does this include breaker operating time?
I am just trying to fully understand this 2-cycle note. Thank you in advance for the advice.
In the table notes, it mentioned clearing times of 0.03sec (2-cycles). What devices clear in 2-cycles (other than fuses)? Does this include breaker operating time?
I am just trying to fully understand this 2-cycle note. Thank you in advance for the advice.






RE: NFPA-70E Table 130.7.c.a question
"Clearing Time" includes all time from initiation of the fault until the arc is extinguished (and stays extinguised).
RE: NFPA-70E Table 130.7.c.a question
What about if the bolted fault current is not in the instantaneous region of the breaker? I would think you need an arc flash analysis to know if this is the case or not.
RE: NFPA-70E Table 130.7.c.a question
RE: NFPA-70E Table 130.7.c.a question
RE: NFPA-70E Table 130.7.c.a question
RE: NFPA-70E Table 130.7.c.a question
As a rule of thumb, the smaller the transformer, the more problems you will have.
RE: NFPA-70E Table 130.7.c.a question
RE: NFPA-70E Table 130.7.c.a question
For 208 V systems, there is a statement in IEEE 1584 that only transformers 125 kVA and larger need to be evaluated. That's probably the origin of the option in SKM.