When exactly half of your home loses electricity while the other half works, you have lost one of the two 120-volt "hot" legs feeding your split-phase electrical service. This is almost always caused by a blown utility transformer fuse or downed overhead service line from Duke Energy or TECO, or a failed double-pole main circuit breaker in your electrical panel. Because 240V appliances (AC compressor, electric water heater, electric dryer) require both legs simultaneously, they will completely fail to operate until the missing leg is restored.
- Split-phase architecture: Your home is powered by two distinct 120V hot phases (Leg A and Leg B). Breakers alternate down the panel busbars. If Leg A dies, every other breaker row in your panel loses power.
- 240V appliances cannot run: Air conditioners, electric ranges, and water heaters span across both Phase A and Phase B to produce 240V. When one leg drops, these appliances receive only 120V or zero voltage and will hum, buzz, or overheat.
- Turn off your AC breaker immediately: Central AC compressors subjected to single-phasing or under-voltage can burn out their motor windings within 30 minutes. Shut off your double-pole AC breaker.
- The utility is responsible half the time: If the dropped leg occurs between the street transformer and your weatherhead, your power company repairs it for free. If it occurs at your meter socket or main panel, an electrician is required.
How North American Split-Phase 120V/240V Power Works
To understand why half a house loses power, you must understand how residential electricity is delivered. Electric utilities (such as Duke Energy or Tampa Electric in Polk County) deliver power via three overhead or underground conductors: Leg A (120V), Leg B (120V), and a center-tapped Neutral wire.
Inside your main electrical panel:
- The metal busbars are interleaved like fingers. Row 1 connects to Leg A. Row 2 connects to Leg B. Row 3 connects to Leg A, and so on.
- Standard single-pole 120V breakers (for bedroom outlets, living room lights, kitchen receptacles) connect to either Leg A or Leg B and the neutral bar.
- Double-pole 240V breakers (for central AC, electric dryer, range, and Level 2 EV chargers) connect to both Leg A and Leg B simultaneously (120V + 120V = 240V).
When one incoming 120V leg drops out (due to a blown transformer fuse, severed wire, or burned breaker contact), every single breaker attached to that specific phase dies, leaving approximately 50% of your lights and outlets without power while the rest continue operating normally.
The 4 Primary Causes of a Partial House Blackout
1. Dropped Utility Phase (Street Transformer or Service Drop)
This is the most common cause. Power utilities protect their street transformers with individual primary line fuses. If a lightning strike, falling oak tree branch, or squirrel blows only one fuse on the pole, one 120V leg to your home dies while the other remains energized. Similarly, high winds can sever one of the two aluminum conductors in your overhead triplex service drop.
2. Failed Main Circuit Breaker
Your main electrical panel is protected by a large double-pole main service disconnect breaker (typically 100A, 150A, or 200A). Inside the main breaker are two independent mechanical contact assemblies tied together with an external plastic handle bar. Over 20 to 30 years of thermal expansion and contraction, internal contacts can carbonize, pit, or mechanically jam, disconnecting one pole while leaving the other engaged.
3. Burned Meter Base Socket Jaw or Panel Lug
The outdoor meter enclosure mounted on the side of your home contains spring-loaded brass jaws that clamp onto the utility meter stabs. In Florida’s hot, humid climate, thermal fatigue and moisture oxidation can cause the aluminum lug or meter jaw to overheat and melt completely away, breaking connection to one 120V phase.
4. Tripped Subpanel Feeder Breaker
If the partial power loss is isolated to a specific wing of your house (e.g., the entire upstairs, mother-in-law suite, or detached garage), the issue is likely a tripped double-pole 60A or 100A subpanel feeder breaker inside your main panel.
If all the dead lights and outlets are located in every other breaker row down your panel (e.g., breaker 1, 3, 5, 7 are dead, but 2, 4, 6, 8 work), you have definitively lost one 120V service leg.
Lost Half Your Power in Winter Haven or Lakeland?
Our licensed master electricians carry digital power quality analyzers to test incoming utility voltage at your meter base and main panel in minutes.
Request Diagnostic DispatchThe Bizarre "Electric Dryer Trick" Backfeeding Phenomenon
Many homeowners experiencing a partial blackout accidentally discover a bizarre anomaly: when they turn on their electric clothes dryer or electric oven, the dead lights in other rooms suddenly flicker back on dimly! When they turn the dryer off, the dead rooms go completely black again.
Why does this happen? It is caused by electrical backfeeding through 240-volt resistance heating elements:
- Your electric dryer heating coil connects directly between Leg A and Leg B.
- When Leg A is dead and you turn the dryer ON, 120V current from the working Leg B travels into the dryer, flows through the heating coil, and exits onto the dead Leg A busbar!
- The dead busbar is now energized with weak, backfed voltage (around 60V to 90V), causing connected lights to glow dimly.
Do NOT leave your dryer, stove, or air conditioner turned on during a partial outage! Backfeeding low voltage (brownout conditions) through compressor motors, refrigerator pumps, and sensitive electronics will cause them to overheat, hum violently, and burn out within minutes.
Who Should You Call: The Electric Utility or an Electrician?
When you lose half your power, knowing whether to call your power company (Duke Energy or TECO) or a licensed electrician saves time and avoids service fees. Follow this decision protocol:
Ask a neighbor on your street if their AC or half their lights are out. If multiple homes are affected, the street transformer dropped a phase. Call your utility company immediately.
Look safely at the overhead power lines connecting from the utility pole to your roof weatherhead. If one wire is dangling or severed by tree limbs, call your utility.
If only your home is affected, the fault may be your main circuit breaker or meter base. Call an electrician to test voltages at the panel deadfront.
Most Florida utilities will dispatch a trouble truck for free to test incoming voltage at the meter can. If they find 120V on both legs, they will advise you to call an electrician.
Florida Weather & Storm Impacts in Polk County
During Central Florida's summer squall season (June through October), severe convective thunderstorms bring 50+ mph wind gusts and intense lightning strikes. Overhead service drops across older neighborhoods in Winter Haven, Bartow, and Lake Wales run through dense live oak and pine canopies.
Falling tree limbs frequently snag overhead service wires. Often, the limb doesn't snap all three conductors—it tears down just one of the insulated aluminum hot conductors while leaving the neutral and second hot leg intact. Furthermore, lightning strikes frequently blow only one high-voltage cutout fuse on Duke Energy or TECO neighborhood transformers, triggering instantaneous half-house blackouts.
From the Field: Dropped Leg Mystery on Lake Shipp
The Symptoms: A homeowner called after an afternoon thunderstorm. Their kitchen lights, refrigerator, and living room TV worked fine, but their central air conditioning, master bedroom outlets, and water heater were dead.
The Diagnostic: Our master electrician opened the panel deadfront and measured voltage across the main lugs:
• Phase A to Neutral: 121.4 Volts
• Phase B to Neutral: 0.3 Volts
• Phase A to Phase B: 121.2 Volts (Should read 240V)
The Fix: We inspected the outdoor weatherhead with binoculars and discovered that a fallen oak branch had ripped Phase B out of the utility overhead crimp connector. We contacted Duke Energy's priority dispatch, verified the service drop was de-energized, coordinated the utility splice repair, and confirmed full 240V restoration across both phases.
How to Protect Your 240V Compressor Motors
Until your power is completely restored, take these critical safety steps to prevent thousands of dollars in appliance damage:
- Shut off your Central AC breaker: Air conditioning compressor motors are designed to operate at 208V–240V. Operating on a single phase (or receiving backfed 60V) causes locked-rotor thermal overheating that will permanently destroy the compressor motor windings.
- Turn off electric water heater breaker: Protect heating elements and thermostats from voltage imbalance.
- Turn off electric range & oven breakers: Avoid dangerous backfeeding through resistive elements.
- Unplug sensitive electronics: Unplug computers, televisions, and gaming consoles on the "working" half of the house in case voltage spikes when the utility restores the missing phase.
Frequently Asked Questions
- NFPA 70: National Electrical Code (NEC), Article 220 & Article 230 (Services).
- IEEE Standard 142 (Green Book): Recommended Practice for Grounding of Industrial and Commercial Power Systems.
- Duke Energy & Tampa Electric (TECO): "Electric Service Standards & Requirements Manual."
- Electrical Safety Foundation International (ESFI): "Understanding Residential Electrical Outages."