CALGARY, Alberta, Oct 23 (Reuters) - Enbridge Inc said on Tuesday it will ration capacity on several of its U.S. Midwest oil pipelines in November after nominations from its shippers exceeded capacity. Enbridge, whose pipelines carry most Canadian crude exports to the United States, said its Line 5 is apportioned by 17 percent; Lines 6A, 62, and 64 are apportioned by 15 percent; and 6B is apportioned by 8 percent. The pipelines, between Wisconsin and southern Ontario, make up much of Enbridge's U.S. network, which carries more than 2 million barrels a day. Enbridge spokesman Graham White declined to specify reasons for the apportionment, which occurs when shippers seek to move more crude on pipelines than available capacity. The operators ration capacity when there is a glut of crude, maintenance on the system or a combination of the two.