On Tue, 22 May 2007 02:54:15 +0000, Larry wrote:

The
ground pin on the dock plug is plainly marked. It's L shaped.

It turns out that the L shaped pin is ground only on the 20 and 30 amp
connectors. On a 50 amp connector it is neutral:

http://www.marinco.com/docs/guides/Boater'sGuidetoACElectrical.pdf