1936 F. A. Westbrook in H. Pender (ed. 3) iv. xvi. 14 Drip-Proof Motors. This type of motor has the upper halves of the heads closed so that materials, including liquids, cannot fall into it.
1960 15 Mar. 171 (advt.) B.S.D. motors (drip-proof or totally-enclosed fan-cooled).