I am replacing a very old heat lamp in a bathroom ceiling with a fan/light/nightlight.
The house is over 50 years old but the heat lamp may have been added in the 80's, when a previous owner did some remodeling. The original house wiring did not use junction boxes in the attic or at light fixtures, but there is one junction box in the attic above this fixture.
I am trying to understand how that wiring worked.
There is 12-3 romex running from the electrical panel into that junction box above the old light.
There are three 12-2 romex lines coming out of that junction box: One 12-2 runs to the switch that controlled the heat light. That line is controlled by breaker 10 in the panel. I understand that. A second 12-2 runs from the junction box directly to the heat lamp. It is also controlled by circuit breaker 10. The third 12-2 runs out from the junction box to a different bathroom. That line is controlled by breaker 12 in the panel.
I am assuming that 10 and 12 share the 12-3 at the electrical panel.
I do not understand why one wire fed the light directly while the other ran through the switch. I would be grateful if someone could explain to me how that works. How does the switch cut the power when there is a second line running directly into the fixture that is always on?
The 2x6 is charred where the heat lamp was attached (4 or 5 inches). Is that likely to have been caused by the heat from the fixture or the wiring? The white romex jackets close to the fixture are browned.
What should be done with the line that ran directly from the junction box to the heat lamp? Should the junction box be rewired so that it can be removed?
I am planning to call an electrician, but I want to understand it before I get an estimate.