46 CFR 111.12-3: -3 Excitation.

In general, excitation must meet sections 4-8-3/3.13.2(a), 4-8-5/5.5.1, 4-8-5/5.5.2, and 4-8-5/5.17.5(e) of the ABS Marine Vessel Rules (incorporated by reference; see § 110.10-1 of this subchapter), except that those for mobile offshore drilling units must meet sections 6-1-7/5.17.1 and 6-1-7/5.19.1 of the ABS MOU Rules (incorporated by reference; see § 110.10-1 of this subchapter). In particular, no static exciter may be used for excitation of an emergency generator unless it is provided with a permanent magnet or a residual-magnetism-type exciter that has the capability of voltage build-up after two months of no operation.