You really can't distinguish between IP 42 and IP 54 just by looking at them. An IP 42 and IP 54 enclosure may be made out out the same metal but, one may be slightly thicker or have a different hinge and latch mechanism or a different gasket material. You should always go by the manufacture rating for the enclosre in question. You also should make sure that you have the right enclosure for the application. NEMA, UL, CSA and IEC all rate areas a little differently so make sure you select the right enclosure.