The Incident Energy levels for something that shares the same interior air space, like an MCC lineup, should be the same through the lineup, because blast pressure from an arc fault incident anywhere in the lineup will be expressed through it. That would not change even if the MCC were labeled as Arc Resistant.
And just so you know, if it WERE Arc Resistant, it must state so with a label a fixed to each and every section with the specific wording “Arc Resistant Equipment” with the IE of the lineup. Some people have used other variations of the wording to get around the fact that their MCC was not qualified as Arc Resistant, usually because it failed the rather difficult testing requirements. There is no AR standard for LV MCCs yet, so the standard that is use for those that have it is the IEEE/ANSI C37.20 standard for Medium Voltage Gear and it’s a tough test standard to meet. It requires that blast pressure be relieved to the point of not creating any hazard to people standing in front of (or to the side or back of if added) the gear, no matter where the incident takes place in the gear. This is measured by placing white cotton blocks around all openings, setting off an arc flash event inside and if any of the cotton turns brown, you fail. So there is no way this can be effectively applied separately to individual buckets at different levels.
Labels in buckets are not the same as the overall Arc Resistant label and not required, so someone likely did that on their own, not the manufacturer, or it’s just for general information. But for the purposes of determining the PPE when a door is opened, it is the IE at the main incoming terminals that counts.
The only time a Main OCPD can be used to reduce the IE is if you have fast acting Current Limiting fuses or if you have a main breaker with “Maintenance Mode”. MM is a separate setting with much lower trip thresholds so that the clearing time is reduced, effectively lowering the IE. But the levels required will put the breaker at risk for nuisance tripping. So you have one set of normal coordinated trip settings, then with a switch closure, a n electrical worker changes to the Maintenance Mode lower settings, but only while working on the equipment.
Something I just remembered regarding that last statement about MM breakers. I recently bid a job for a national food producer where the corporate standard for MCCs was calling for MM breakers on all feeders of 400AF or higher. Ostensibly that could be used to reduce the IE on the DOWNSTREAM equipment when engaged. But it would not reduce the IE in that MCC bucket because it would be based on the line side IE. But it made me wonder if someone misinterpreted that on yours?
