Electrical – Why is the electric going on only in half the house

I am pretty sure what you have is classic case of voltage drop. Ballasts for vapor lights and some cheap light sensors for incandescent par bulbs will be tricked or drop output, so light goes out and has to restart when voltage is restored. The reason for the sudden drop is really the concern. Since the heat pump employs a fairly large motor, it draws a lot of current at start up. This is called inductive kick. It takes a few seconds for the coils of the motor to saturate and start he armature spinning in the magnetic field. Since the coils are a dead short until saturation is achieved, they draw large current. E = I/R, ohms law explains this. So what is the solution? You may need to have the heat pump motor checked out or add a motor starting capacitor across the windings. I cannot tell you what size capacitor you will need as it can vary widely depending on motor size. This is a very common problem in residential services that are close to current capacity with an unbalanced motor load. Even though you may have a 100 or 200 amp electrical service, it can be overtaxed temporarily by an unbalanced motor start up

It sounds like you have or had knob and tube wiring that might have been converted,
which consists on a Hot and a Neutral With no Ground (which is needed for GFCI, but

sometimes use the Neutral pigtail to mickey mouse false ground,).

*You can add a ground with a wire to copper pipe from sink’s water supply or run to basement)

14-2 wire is rated at 15 amps MAX

12-2 wire is rated 20 amps MAX

If you splice or run off a 14 Gauge to a 12 Gauge you must treat it as a 14 gauge

The higher the gauge the smaller the wire weakest link being 14 while using 14 to 12

If you are rewiring the whole bath and rooms then 12 gauge is the sanest answer

12 Gauge handles 15 or 20 amperes 14 should not be more than 15 for safety reasons

(When using 12 on 20A breaker use screw terminal as opposed to tension insert)

Testing for a hot wire when there is no labeling on wire casing (sheath) use a meter on ~ AC

And use a ground from ground cold water pipe and then touch pos lead on each wire (they do sell polarity test tools also don’t always work with conversion wiring)

The 110 – 120V reading wire is the hot

Hope that answers your question.

Sincerely BEAR