Half My House Lost Power: Causes and What to Check First

Half the lights are out, the other half work, no breaker looks tripped, and the dryer tumbles without heating. That pattern has a name.

Short answer: half your house lost power because one of the two 120 V legs feeding your panel is gone. The cause is usually a failed connection between the utility transformer and your main breaker: on the utility's service drop or lateral, in the meter socket, or on one pole of the main breaker. Call your utility's outage line first. If they find normal voltage on both legs at the meter, call a licensed electrician.

Why does only half the house lose power?

US homes get split-phase service: two hot conductors (the legs) and a neutral from the utility transformer. Each leg to neutral is nominally 120 V, and leg to leg is nominally 240 V. Breaker positions alternate between the two legs down the panel. The details are in 120V vs 240V circuits explained.

Lose one leg and:

• Every 120 V circuit on that leg goes dead. Roughly half of them, scattered around the house rather than a tidy half of the floor plan, because circuits are assigned to legs by panel position, not by room.
• Every 120 V circuit on the other leg works normally.
• 240 V appliances lose their 240 V supply. The range, electric dryer, water heater, central AC or heat pump and any Level 2 EV charger either stop or behave strangely.

What does a lost leg look like?

The usual symptoms:

• Lights and outlets dead in some rooms and fine in others, sometimes both in the same room
• An electric dryer that runs but doesn't heat. Its drum motor typically runs on one leg at 120 V, while the element needs both legs
• Range elements or the water heater not heating; the indoor furnace fan may run while the outdoor AC unit sits idle
• Weak or dim power on the "dead" circuits, sometimes coming and going. A 240 V appliance connected across both legs can bridge some voltage from the live leg onto the dead one, so dead-side lights may glow dimly or flicker as the water heater or dryer cycles
• Nothing brighter than normal. That's the key difference from the next fault

Lost leg or open neutral?

The two get confused, and they aren't equally dangerous.

If anything is brighter than normal, treat it as a possible open neutral: unplug electronics and call the utility right away.

What causes it, most likely first

1. The utility side. A burned or broken connection where the utility's conductors join yours at the weatherhead or in an underground splice, a conductor damaged by wind, ice or a falling limb, a failed underground cable, or a connection problem at the transformer. This is utility equipment, and they repair it, usually at no charge to you. Where their responsibility ends is explained in who owns what on your electrical service.

2. The meter socket or service conductors. A corroded or burned jaw in the meter socket, or a failed termination on the service entrance conductors. The socket is normally your equipment, so this is an electrician repair, and the utility has to pull the meter first. See meter socket and service entrance explained.

3. One pole of the main breaker. The main breaker is a two-pole device. If one pole's contacts, its line-side lug or its connection to the bus fails, that leg stops at the panel even though the utility is delivering it. An electrician diagnoses and replaces it.

4. A tripped breaker feeding part of the house. If the dead area is a wing, an addition, a garage or a basement rather than scattered circuits, look for a tripped double-pole breaker that feeds a subpanel, or several tripped branch breakers. If a breaker trips again after one reset, see why does my breaker keep tripping. If it's really one room or a few receptacles, work through outlet not working troubleshooting instead.

What can you safely check?

None of this involves opening anything beyond the panel's outer door.

1. Check the breakers. Look for handles sitting between ON and OFF. Reset a tripped one once: fully OFF, then ON. If it trips again, leave it off.
2. Briefly test a 240 V appliance. Run the dryer on a heat setting or turn on a range element. If it heats normally, both legs are reaching the panel and the problem is downstream, in a feeder or branch circuit. If it doesn't, a lost leg is likely.
3. Ask the neighbors. If homes nearby have the same half-power pattern, the problem is almost certainly the utility's transformer or shared lines. If they're fine, it can still be your own service drop.
4. Map the dead circuits. Plug a lamp into outlets in the dead rooms, or check them with a non-contact voltage tester, proving the tester first on an outlet in the half that works. A pen only tells you live or not live, and on a lost leg it may still beep at a "dead" outlet because of the bridged voltage described above.
5. Write down what you found: which circuits are dead, which 240 V appliances fail, and whether anything is brighter than normal.

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Who do you call, and in what order?

1. The utility's outage line. Report partial power, not a full outage, and mention the 240 V symptoms. A technician checks voltage at the meter and fixes anything on the utility's side.
2. A licensed electrician, if the utility confirms both legs arrive normally at the meter. The fault is then in your meter socket, service entrance conductors or main breaker.

If there's smoke, a burning smell, sparking or buzzing at the meter or panel, don't wait for a callback. Move away from it and call 911 as well as the utility.

What should you do while you wait?

• Unplug sensitive electronics such as computers, TVs and networking gear, on both halves of the house.
• Shut off large motor and 240 V loads. Set the thermostat to OFF and leave the dryer and range off. Switching off the double-pole breakers for the water heater, dryer and AC also stops those appliances bridging voltage onto the dead leg, where motors can run hot on low voltage.
• Know where your service disconnect is: the main breaker, or on newer homes an outdoor disconnect, in case you need to shut everything off.
• Never pull the meter, break its seal, or open the panel's inner cover. The meter jaws, service conductors and main lugs stay energized with the main breaker off, and no breaker of yours protects them.
• Never plug a generator into a dryer or range outlet. Backfeeding the panel without transfer equipment can energize the utility's lines while a crew is working on them.

Why is this utility or electrician work?

Everything that causes a lost leg sits on the line side of your main breaker, where no overcurrent protection of yours applies. The utility's drop, lateral and transformer are outside the NEC entirely and theirs to repair. The meter socket, service conductors and main breaker are yours, but working on them means pulling the meter first, and finding which one failed means measuring voltage on live service equipment. That's licensed-electrician work.

Standards and code reference

The standards behind this guide, for looking up in the edition your jurisdiction has adopted:

• NEC 90.2: scope; installations under the exclusive control of an electric utility are not covered by the NEC
• NEC 230.70: service disconnecting means, including its readily accessible location
• NEC 230.85: outdoor emergency disconnect for one- and two-family dwellings
• NEC 702.5: transfer equipment required when an optional standby generator is connected to premises wiring

Code editions and local amendments vary. Confirm the adopted edition with your AHJ, and treat manufacturer instructions as governing wherever they are more restrictive.

Where to go next

• How to reset a tripped breaker
• Lights flickering in the house: causes
• What is a service disconnect?
• Overhead vs underground service

More in our electrical panel guides.