Half the house has no power: what it usually means and what to do

Most homes receive power as two 120-volt legs that together make 240 volts. Every other breaker in the panel is fed by one leg or the other, so when one leg fails, roughly half the circuits go dead while the rest keep working. The 240-volt appliances, such as the range, dryer and air conditioner, may stop, hum or run weakly because they need both legs.

A failed leg can come from the utility side, such as a damaged transformer connection or a service drop pulled loose, or from the house side, such as a burned connection at the weatherhead, the meter base or the main breaker.

Sometimes the problem is not a full failure but a loose connection, often on the neutral. The symptoms are lights that get brighter in some rooms and dimmer in others when appliances turn on, bulbs that burn out quickly, or electronics that fail. This is more dangerous than a clean outage because voltage in some rooms can rise well above normal.

A loose neutral should be treated as urgent. Switch off sensitive electronics and large appliances and call. An electrician measures voltage on both legs under load and finds the loose connection, which may be at the panel, the meter base or the utility connection.

Voltage at the main lugs on both legs, then at the meter base. The main breaker for heat, damage or a failed pole. The service conductors and connections at the meter base and weatherhead for burning or corrosion. The neutral connection for tightness. Once the failed point is found, it is repaired and the voltage is checked under load.

If the meter base is burned or the main is failing, replacement may need the utility to pull the meter, and an older panel may be better replaced than repaired.

Half-power problems cluster around two kinds of weather. Storms and ice put limbs on the service drop, stretching or breaking one leg or damaging the neutral. Long hot spells keep air conditioners running hard, and a service connection that was already loose heats, cools and loosens further until one leg drops out.

That is why the problem often appears at the worst moment, in the middle of a heat wave or the morning after a storm, and why the repair is worth doing properly rather than waiting for it to come back.

While half the house is out, the half that works may be seeing unstable voltage. Unplug computers, televisions and anything with a circuit board, and switch off large 240 volt appliances such as the dryer, range and air conditioner at their breakers.

If lights are flickering or running unusually bright, switch off the main breaker until the cause is found. It is a short inconvenience compared with replacing a houseful of electronics.