**This strongly suggests a loose, damaged, or disconnected main neutral—and the 50-amp breakers create a separate fire hazard. Stop using the electrical system until it is inspected.**

In a normal 120/240-volt home supply, the neutral keeps both groups of 120-volt circuits at the proper voltage. When that connection fails, plugging something in can make voltage drop on one group and rise on the other. That explains why some lights dim while others become unusually bright, and why heaters behave differently depending on the outlet. Appliances can receive dangerously high voltage. This is a likely diagnosis, but an on-site inspection must confirm it. [Power Monitors’ explanation](https://powermonitors.com/whitepapers/identifying-loose-neutrals/)

Take these steps now:

- **Switch off the main breaker if you can safely operate its normal handle without removing covers.** If the panel is hot, buzzing, sparking, or smells burned, stay away and have the utility disconnect power.
- **Call your utility’s emergency/service number and a licensed electrician today.** Tell them: “Lights brighten and dim when loads change; I suspect a lost neutral.” Explain the 300-foot underground aluminum run and the breaker replacements.
- **Have the electrician restore correctly sized breakers before power is restored.** Ordinary lighting and receptacle circuits generally require 15- or 20-amp protection, depending on their wiring. A 50-amp breaker can allow those wires to overheat without tripping. Larger breakers cannot correct voltage problems. [CPSC wiring-hazard guidance](https://www.cpsc.gov/s3fs-public/518.pdf)

The neutral fault could be at the utility connection, meter equipment, either end of your buried cable, or within the cable itself. A poor aluminum termination or damaged insulation allowing underground corrosion could explain why it worked for six months before deteriorating. [Power Monitors](https://powermonitors.com/whitepapers/identifying-loose-neutrals/)

The electrician should also assess the cable’s capacity and voltage drop over 300 feet, and verify grounding and bonding. **Leave the walls open until the wiring has been inspected. Don’t keep plugging in loads to investigate or retighten service connections yourself.**