Low voltage circuit breaker arc flash
Low voltage circuit breaker arc flash
(OP)
I am using IEEE 1584 spreadsheet to calculate the arc flash energy downline from a low voltage circuit breaker. The maximum available fault current is 26kA and the Digitrip is set to 18kA instaneous trip. The cell in the spreadsheet turns orange noting 'out of range'. What range are they talking about? 18kA is well below the 26kA that is max available. Any help would be much appreciated.






RE: Low voltage circuit breaker arc flash
I suspect the calculated arcing fault current is less than 18 kA. In addition, IEEE 1584 recommends a second evaluation at 85% of the calculated **arcing** fault current, since arcing current is highly variable.
I haven't used the spreadsheet in many years, but you should check what the calculated arcing current is.
"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg
RE: Low voltage circuit breaker arc flash
I'm guessing that you input 26kA as the source (1.5MVA transformer with Z=7%), but there's a large impedance between the LV breaker and the equipment you're analyzing.
All of this results in a much lower bolted fault current used in the equation. As dpc pointed out, the arcing fault current is much less than the bolted fault current (remember to check your conductor gap), so you're probably not getting the trip unit to pickup.
RE: Low voltage circuit breaker arc flash
RE: Low voltage circuit breaker arc flash
"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg
RE: Low voltage circuit breaker arc flash
Perhaps the 1.3 factor is equivalent to a +10% breaker tolerance and an 85% fault? 1.294=1.10/0.85
RE: Low voltage circuit breaker arc flash