Linda, you bring up an interesting question. From what I can tell, under the Category listing, there are only 6 major professions categorized - Actors, Authors, Artists, Aviators, Military, and Musicians. That's not to say that there aren't others lurking out there, but based on that page alone, there's not a proper category currently for a Public Utility worker.
I don't have an answer - but I think it would be a healthy discussion to talk about what sort of categories should be established to properly categorize professions. Considering what appears to be standard so far, there are what I would consider a very long list of potential categories for all the other jobs people have done that don't currently fit in the existing list.
It does appear that this question was asked before (August 4, I believe, by Star Kline?) about creating and standardizing Professions and it does not appear there was a consensus.
To answer your question directly - yes - you would want to establish the chain of professions to show the sub-categories reaching to the specific profession your ancestor held, so I think you're on the right track. But longer term, we really should have a committee at least to study professions and how to categorize them at WikiTree.