I'm currently doing some renovation in my bathroom, and while the walls are open, running updated cable where I have access. This also includes the addition of a GFCI outlet. It's a 1940s home, and the bathroom and its wiring are original. I've lived here for 17 years, and just purchased it in December. Now that I own it, I am starting to correct all of the issues I know of.
With the intention of having a dedicated circuit for the new outlet, I went all the way back to the breaker panel with 12/2+G Romex. Currently, this circuit has many branches throughout the house, and the intention is to ultimately isolate the bathroom when I free up panel space. The breaker panel is full, so a simple "new circuit" is not immediately possible. The new 12/2 was installed at the first "half" of the circuit so far - forming the "trunk" so to speak - and all but 2 of the branches remain unchanged.
But the issue at hand is that one of the outlets on the circuit failed the day after I ran the new cable. EDIT: The dryer and heater would not work, and there were no audible or visible signs of a problem, nor a burning smell. Due to the fact that the current wiring is an absolute mess, I have drawn a schematic with more specifics to illustrate the current configuration rather than trying to fully explain. I am aware of all of the code (and plain stupidity) related issues that are present, and intend to correct them and reallocate circuits incrementally once I finish the bathroom renovation, and then map out the rest of the wiring.
At the end of one of the branches in the basement, is a receptacle that has my clothes dryer plugged in. I work from home, and my office (with its own circuit) is also in the basement. The basement is unfinished, so we have areas separated by shelving or furniture. 2-3 months ago, I added a space heater (set low), just to take the edge off on colder days, figuring while the dryer is not running, the heater set low would be fine there. Note #1: I have another space heater on my office circuit. Note #2: I was not aware that the laundry area was not on its own circuit until I started this. Regardless of these facts, this setup has been working without issues since I started using it. So, the question is that how, after 2+ months, did the old receptacle fail, and when replaced with a brand new one, fail again?
Also... The breaker did not trip. All other outlets are working fine, and the new bad receptacle is reading ~36v to neutral, and ~40v to ground. I get ~126v at every other known branch on the circuit. My only assumption is that the lower resistance of the 12/2 changed the dynamics of the whole circuit somehow?