The 42 circuit limit did indeed result from a fire in the Waldorf-Astoria Hotel in New York in 1928. This was a lighting panel wired with type R wire. This story was confirmed by the late Anthony Montouri, Chief Inspector, New York Board of Fire Underwriters. It was judged at the time that there was too much insulation and braid in one enclosure, and the 1933 NEC in Section 1303g. established the 42 circuit limit. It may have been over-reacting. To change this would require extensive testing and I doubt there is any interest willing to put up the money for such an investigatrion.
Creighton
