Originally Posted by cpaharley2008
Actually these Marinco connectors were originally made for marine applications, here is a good video as to how to use and connect these sets as well as explain their limits.
DIY Shore Power | West Marine
in the video it clearly shows use of the locking connection, without the locking ring.
"Originally" the Marino line was intended for marine use - thus the name - but the underlying L5-30 connector is the same existing locking 30-amp three-wire design which has been used for all sorts of industrial and commercial equipment since the 1930's, with no provisions for sealing. The weatherproofing is very much an add-on for marine/RV use, adding security and weather resistance, and not part of the L5 design.
(I didn't watch the video - few online videos are worth it on a rural mobile connection)
I see on that page that Marinco now also has a newer and supposedly better add-on to the NEMA L5-30, instead of the threaded ring - the "Easily Engaged Locking (EEL) System". Unfortunately, their "full line" of cordsets and adapters apparently doesn't include any right-angle products for the trailer end, and the cords are useless for RVs anyway without a custom adapter because they have the locking connector on both ends, instead of a TT-30 (the standard 30-amp campground connector) on the end for the campsite outlet.
Anyone interested in another connector design which should latch securely and is designed to be weather-resistant - and isn't an adaptation of another design - might want to look for the SmartPlug
. It is a new design I've seen in forum discussions, which pushes straight in then latches, and has rubber (or similar) seals. Like Marinco's products, it was originally intended for marine shore power use, but the SmartPlug is not based on the NEMA L5 connector. Like Marinco, SmartPlug does not offer a cord with their connector on the trailer end and a standard TT-30 on the campsite end, but at least they do offer separate connectors so customer can custom-build a cord.