2018 IEEE 1584 6.10 says "When a model of the power system is developed, the equipment compartmentalization and fault location need to be considered. The arc fault could occur on the line side, bus side, and load side of protective devices located in different compartments... ...When evaluating the incident energy at an arcing fault location in the system, the interrupting time of the protective device upstream from the point of the fault must be considered. An integral “main� overcurrent protective device may be considered in the calculation if it is adequately isolated from the bus to prevent escalation to a line-side fault. When the integral main overcurrent protective device is not adequately isolated from the bus, the upstream protective device must be considered as protecting the main and bus."

I see lots of discussion on this subject and "propagation" on this forum in the early 2010s, but not much since the 2018 standard came out.

How are all of you currently determining/defining:
"compartmentalization" and "adequately isolated"?

Engineering judgment based on the construction of the equipment.

Mike

Thanks, Mike. Are there standards or manufacturer's information that you are consulting? Do you have default assumptions? Or are you eyeballing it on a case-by-case basis?

I put eyes on it. Shop drawings for the equipment are helpful as well.

Mike

Basically gear built to UL standards, like switchboards and MCCs are not compartmentalized in a manner that would be beneficial for arc flash studies
However, most medium voltage equipment such as switchgear and MCCs is compartmentalized.

The iffy products are LV drawout switchgear where some is fully compartmentalized but some manufacturers have openings between the cross bussing and the cable compartments.

I have a hard time with

Isn't that what buckets do? Each feeder bucket is isolated from the bus, and the main breaker is almost always in a different section. I have a hard time imagining a fault in a feeder bucket propagating to the line side of the main.

JBD, are there particular standards you refer to?
E.g., UL gear = NOT compartmentalized, ANSI something gear = compartmentalized? Do those standards actually say anything on the subject, or is this your engineering judgment?

The standards JBD is referring do not talk about arc flash. Those references are equipment/construction standards.

Mike