In results calculated using IEEE 1584-2018 equations, I have noticed that Incident Energy values are lower for Shallow enclosures than for Typical enclosures (when all parameters except Enclosure Depth are identical). See the attached image for some examples.



In past topics on this forum, members have commented that calculated Incident Energy will be lower for Shallow enclosures (see 2018 IEEE 1584 - Arc Flash and Shallow Enclosures and Implementing New 1584). Having looked closely at the Intermediate Incident Energy equation (Eq. 6), I can see why a lower energy value is generated.

What I would like to understand is why a shallower enclosure would in practice produce a lower Incident Energy. My simplistic understanding was that the larger the enclosure the more volume is available for the arc to disperse (and the effect of the arc would therefore be lessened) and conversely the smaller the enclosure the more focused the effects of the arc would be.

If anyone can shed any light, I would be very grateful.

I've also just read a statement in IEEE Std 1584-2018 Annex G (G.9.4) which that states that Incident Energy test results were higher for enclosures with depth <= 203.2 mm (8 in) than those of depth > 228.6 mm (9 in). Is that a typo?

Here's a screenshot of the aforementioned excerpt...