Paul,
In my opinion the shower space is defined by the shower enclosure or shower curtain. The bathtub space is the bathtub itself and the space extended vertically above the tub. The rule in 550 prohibits receptacles from being within 30" of these spaces. The rules in 380 and 410 only prohibit installation within the space. I don't know why the rule is different for mobile homes, but it is. There have been other cases of rules being more stringent in Article 550 then in Chapters 1-4. One example that I can think of is the requirement for 4 wire branch circuits for electric dryers and stoves. This rule was in 550 3 or 4 code cycles before it was in Chapter 2.
Don(resqcapt19)
