I don't think circuit is a very useful tag, as I can't think of any time you'd use it as the only tag on a post. I also don't think many folks would use it to find questions they might be interested in.
The tag should probably be removed.
I created a new tag, refinishing (because we have the other tags basement-refinishing and hardwood-refinishing this seemed like the logical choice for a name), and merged the typo tag refinsh into it, without creating a synonym.
End result: all the questions that had the bad tag on them now have the new tag instead.
I think when it started, the tag was for questions that had to do with the electrical system beyond the service drop. Transformers, types of systems, etc. However, it's likely not used properly, and can probably be killed.
The tag can be removed from any questions that are not asking about the distribution of electricity.
wire is only a good tag on questions that ask specifically about wire. For example: "Is there a difference between stranded and solid wire?", "What material is the insulation of THHN wire?", etc.
If questions are tagged with the wire tag, but are not discussing wire. Then that tag should be removed from the post.
I think you could try to retag some if its absolutely clear what they mean, but I would wager that most of them are not specific enough.
Adding a more specific tag in to help future searchers is good, but I agree that the generic [gas] tag is required.
I would point out that in some countries "gas" is the only term people would use to describe what others would call natural gas and or propane because gas is not a shorthand for gasoline. Some people would never tag propane or natural gas as its not a term they would ever be familiar with.