I believe the intent is to use the RMS value. Everything we do is in terms of RMS.
Then again I may be the only person who deals with the NEC that would take the word maximum and relate it to the peak value.
Pete
Equipment ratings are expressed in terms of RMS. Also, the second sentence of 110.24(A) speaks of the calculation used to determine the maximum available fault current. Such calculations are always performed in terms of RMS current. The idea is to show the operator or maintenance person that the available fault current is no higher than the equipment's rating, evidence that the system was designed and installed safely. Bringing a peak value into the process would confuse, not clarify, the situation."The word ?maximum? was added in an attempt to clarify the requirements as an equipment rating consideration and not for use in conjunction with arc flash hazard analysis."