What is the point of the existence of TT-30R along side 5-30R?

[Flicker Index]

Is there a valid reason for both versions of straight plug system to exist?
It's not like one offers additional functionality.. such as in the case of twist lock

 

[ModbusMan]

TT-30R strikes me as a more weather- and abuse-resistant option, while (L)5-30R is more for indoors.

 

[infinity]

According to Leviton their TT-30R is labeled Recreational Vehicle Use Only.

 

[zbang]

TT = "travel trailer", and it actually is a NEMA type! (pg 140 in ANSI/NEMA WD 6-2002 Wiring Dimensions; wasn't sure I'd find it there). The origin story should be interesting. (Remember all the non-NEMA twistlocks in the 60s and 70s?)

It also doesn't appear to be any more weather resistant than a 5-30 (which I've never seen in the wild, only L5-30s).

 

[Jraef]

40 years in this business and I have never encountered a 5-30 plug or receptacle. TT-30s, all the time, L5-30s, sometimes. But no 5-30s.

As I heard it, TT-30 was developed and heavily promoted by Airstream for trailer parks all across the country, so that people getting into the trailer life in the 50s could be confident in being able to plug in when they got to one.