hi
As far as I know there is no industry standard for terminal boxes....but they are governed by the IP rating of the motor...ie. protection against ingress of dirt,water etc. and also hazardous area use motors, such as flameproof motors etc.
hope this helps
Jeff
I have an old version of NEMA MG-1 ( 1990). It has a Table 20-3 that related terminal box size and ampacity and voltage. Section 20 of this stndard in which the table was located was for large induction machines - > 100 hp.
In ANSI regions, reference 1999 NEC §430-12 Motor Terminal Housings
or IEEE Std 841-2001 §6.5 Main terminal boxes and terminal leads
or NEMA Std MG 1-2003 §4.4 …Dimensions