I hadn't seen anyone comment on this but it also applies to time at load, so if you are loading it up heavy and then ran for a long time it may heat up more than you were used to. If it is all of a sudden heating up more and ALL detail on loading etc are the same as before, yo may have an issue. If it's heated enough to damage the winding's I think you would know pretty quickly but smell or magic smoke escaping. You also need to consider what others are alluding to, review your actual Watt loading and then determine if you are with in reason or if you may be actually over loading the ZW. Anything over about 180W constant would probably be considered an overload situation. does not matter if it is only accessory lights either.
Lastly, if you have bad connections on your track or dirty connections, that will affect conductivity, which will increase your current draw as well.
