Power to half a house is typically lost when one leg of the split-phase electrical system fails, often due to a loose or damaged wire, a faulty breaker, or an issue with the utility’s service line. This results in only one of the two 120V legs delivering power, affecting circuits connected to the failed leg. Let's look into different reasons for half of the power going off in more detail:

1. Lost Hot Leg (Phase) in a Split-Phase System:

• In most homes, power comes from two 120V legs (phases), which together provide 240V for larger appliances (e.g., dryers, stoves). If one leg of power is lost due to a loose connection, damaged wire, or utility issue, half of your house will lose power. Circuits connected to the working leg will still function, while those on the dead leg won't.
• Symptoms: Half the house loses power, especially 240V appliances like dryers, stoves, or AC units. Some outlets and lights may still work on the other leg.
• Most Likely If: There’s no obvious internal problem, and your neighbors don't have the same issue.
• How to Check:
• If they aren't working, it suggests one leg is out.
• Measure the voltage at the breaker panel. Between the two hot legs, it should read 240V. If it reads 0V or significantly lower, you’ve likely lost a leg.
• Measure voltage between each leg and ground. Each should read 120V. If one reads 0V, you've lost a leg.
• Solution: Call your utility provider to inspect the service line, as they can determine if the problem is with the incoming power from the pole or transformer. If the issue is on their side, they will fix it; if it's inside your home, an electrician will need to repair it.

      2. Burnt or Loose Wire:

• Over time, wiring can degrade, especially at the service entrance or behind the meter. This can lead to a wire burning out or becoming loose, causing one leg of power to be lost.
• Common Case: Homeowners have found wires burnt or severed behind the meter due to overheating or poor connection, which interrupts power to one side of the house.
• Symptoms: Flickering power, intermittent outages in certain areas, possibly near heavy-load appliances like HVAC, stoves, or near the main breaker panel. There may be a burnt smell or visible signs of damage.
• Most Likely If: There’s no external power outage, and you notice intermittent outages or flickering in specific areas of the house, often near high-load appliances like the meter or main panel.
• How to Check:
• Look for burnt, frayed, or melted wires at the breaker panel or behind the meter. Do not touch; just visually inspect.
• If you feel comfortable, carefully check for loose connections in the panel or at major appliance connections (with power off).
• Solution: Have an electrician inspect for burnt or loose wires at the main breaker or behind the meter. The utility company may need to disconnect power temporarily for the repair.

      3. Backfeeding Through 240V Appliances:

• In some cases, 240V appliances like a dryer or water heater may momentarily power circuits on the dead leg by backfeeding through the working leg. This can cause the power to flicker or return intermittently, but is unsafe for the appliances.
• Symptoms: Power returns or flickers when large appliances (like water heaters or dryers) turn on, but then cuts off when they cycle off.
• Most Likely If: Some circuits seem to regain power only when large appliances are running.
• How to Check:
• Turn off the breakers for large 240V appliances.
• If power to affected circuits goes completely dead without intermittent flickering, this confirms backfeeding was occurring through the appliance.
• Check voltage at the panel to confirm one leg is dead (as mentioned in lost hot leg).
• Solution: Turn off breakers for all 240V appliances to prevent damage while the issue is being diagnosed.

  4. Faulty Main Breaker or Panel:

• The issue could also be due to a malfunctioning main breaker or a poor connection in the breaker panel, causing one leg of power to fail. A visual inspection may reveal signs of damage or loose bus bars.
• Symptoms: Power loss in large sections of the house, even though the breakers aren’t tripped. Resetting the main breaker doesn’t solve the problem.
• Most Likely If: There are signs of wear, loose connections, or overheating in the panel.
• How to Check:
• Turn the main breaker off for 30-60 seconds, then back on. If the power doesn’t return, it may be faulty.
• Look for visible signs of wear or damage on the main breaker or bus bars in the panel.
• If you can measure voltage, check the main breaker’s output. If voltage is low or zero, the main breaker could be the issue.
• Solution: If resetting the main breaker doesn’t work, an electrician will need to test and possibly replace the breaker or inspect the panel for internal issues.

 5. Utility Side Problems:

• Sometimes the problem is outside the home, such as a bad transformer or damaged service line leading from the pole to your house. If neighbors on the same transformer have similar issues, it’s likely a utility problem.
• Symptoms: Sudden power loss after weather events, utility work, or external incidents. Neighbors may also be affected, and no internal issues are found.
• Most Likely If: There’s no sign of internal damage, and the problem started suddenly, especially after external factors like weather or utility work.
• Solution: Call the utility company and report a partial power loss. They will check the lines and transformer and repair any issues. You can consult neighbors to confirm this is an issue.

In general:

• Lost hot leg is common with external power supply issues.
• Burnt or loose wires are common in aging or poorly maintained systems.
• Backfeeding typically occurs with large 240V appliances.
• Faulty main breakers or panels affect older systems.
• Utility problems are more likely after weather or utility-related incidents.

If you need to replace the wiring as a result of half of the power going off, NNC has a vast catalogue of cables to choose from.