Hello,

I am studying arc flash and have a question. IEEE 1584-2018 adds a enclosure correction factor that requires enclosure size.
If the enclosure have compartments, which size do we use to determine the correction factor? Is the size of the enclosure or compartment?

First we are modeling worst case so it’s an arc on the incoming side of the enclosure. Second the test data is for an open box without obstructions. Real enclosures aren’t like that.Third it’s radiative energy so it bounces off walls, etc. The more “hall way” like the enclosure the higher the energy. If it’s larger, shallower, and more “medicine cabinet” like the energy will just dissipate as if it radiates in all directions like a hemisphere. Souse outer dimensions of the enclosure. A side compartment like medium voltage MCCs, some larger MCCs, etc. narrows the door opening but also reflects/absorbs energymonnthe back side. Breakers, contactors, etc. also add surface area and absorb energy. But the model and standard don’t have provisions for the energy lowering effect of obstructions so we conservatively ignore them.

For MCCs, Switchboards, and Switchgear, we typically will do a calculation for the line side of the main breaker cubicle and the smallest cubicle / enclosure downstream of the main breaker. Typically smaller cubicles in this type of equipment results in slightly higher arc flash energy. The end result is that the main cubicle gets a label and then the main bus of the MCC, Switchboard, or Switchgear gets another label based upon the smallest enclosure. Sometimes the smallest cubicle/enclosure is a TVSS device, or metering compartment.