Arc Flash Hazard Assessment on SWGR CB
Arc Flash Hazard Assessment on SWGR CB
(OP)
Hello. I am trying to assess whether or not it is safe to operate switchgear with possibly very high incident energies. NFPA 70e table 130.7(c)(15)(A)(a) says that normal operation of a circuit breaker or switch does not require arc flash PPE. My question is, what if the calculated incident energy of the switch or CB is very high, like >100 cal/cm2? Is there a value of IE above which it is NOT safe to operate the CB?
Thanks
EE
Thanks
EE





RE: Arc Flash Hazard Assessment on SWGR CB
RE: Arc Flash Hazard Assessment on SWGR CB
One possibility is remote operation of the breaker.
With an incident energy level that high, did the study engineer look at ways of reducing that IE?
RE: Arc Flash Hazard Assessment on SWGR CB
EE
RE: Arc Flash Hazard Assessment on SWGR CB
The table is not concerned with the level of IE as operating a breaker is considered normal, i.e. it is what the breaker is designed to do. As long as it has been maintained, is installed IAW manufacturer's directions, has all the cover screws in place or latched and there is no indication of impending failure such as noise from arcing or any overheating, then you not doing anything that would cause an arc flash by operating the breaker.
Just curious what software you used for the study?
RE: Arc Flash Hazard Assessment on SWGR CB
That's interesting. I have had a few discussions about this clause and I generally agree with your interpretation. Others insist on full flash suits for doing routine switching operations, on the basis that an arcing event theoretically could occur during routine operations.
RE: Arc Flash Hazard Assessment on SWGR CB
RE: Arc Flash Hazard Assessment on SWGR CB
RE: Arc Flash Hazard Assessment on SWGR CB
I curious on the very high IE as I have not seen many that high. Did you use the utility's available fault current and if this is the first main bus on the transformer secondary side, did you model back to the utility primary protective device?
RE: Arc Flash Hazard Assessment on SWGR CB
Yes, this is the first bus downstream of a 2MVA transformer with Z of 4.6%. I do many of these studies and I find that nearly always the main disconnect has a dangerously high IE. I often require that the main disconnect is remotely operable. FYI, the IE on this particular project is ~78. I mis-stated earlier it being > 100.
The utility has not provided the available fault current (nor do they ever). What I typically do is find out what utility transformer feeds our station transformer. I put the utility's transformer in my model and then use infinite bus in front of that transformer. Sometimes I can even find out the feeder length and size.
EE
RE: Arc Flash Hazard Assessment on SWGR CB
You should be able to find out the actual values.
I have reviewed arc flash studies performed by major companies and found that many used unrealistically high utility fault currents. For example one report had the utility fault current at 40,000A at 34.5kV when I got the fault current from the utility it was actually 5,200A. Big difference. I also found that the study did not take into account the recloser 2 line sections away.
So bottom line is I do not believe your incident energy values represent the actual incident energy values present.
RE: Arc Flash Hazard Assessment on SWGR CB
You can't expect the utility to call you every time they make a change to their grid. There are so many variables that can change over time that the best approach is to be cautious. The goal is to prevent putting personnel in a position where they can be hurt.
RE: Arc Flash Hazard Assessment on SWGR CB
Most grids are fairly stable and changes are one reason why IEEE 1584-2002 has a 5 yr time frame on reviewing and updating the study.