The 2017 Edition of the National Electrical Safety Code (IEEE C2) contains Table 410-1 Clothing and clothing systems for voltages 50 V to 1000V (ac).

This table lists the maximum arc rating necessary for protection from the arc flash hazard based on equipment type.

4 cal/cm^2 is listed for panelboards 50V to 250 V

Note (1) [applies to entire table]
This table was developed from fault testing based on equipment type and is independent of fault current unless otherwise noted.

Note (2) [specific 50 V – 250 V panelboards]
The arc rating values for the panels are based on industry testing by two separate major utilities and one research institute and that the arc will not sustain more than 2 cycles.

This week’s question:

Have you used 4 cal/cm^2 from NESC Table 410-1 for panels up to 250V?
Yes
No
Never heard of it

Note the scope of the NESC prior to use. It may not be appropriate for many forum members.

To add to the discussion: OSHA letter of interpretation