Customer Says Half The House Has No Power, Translation To Fault Decision Tree

Why this matters

"Half the house has no power" is the single most reliable verbal signature of a lost line (open hot leg) or an open service neutral, and both are upstream, potentially dangerous faults. A 120/240 V single-phase service feeds the panel on two hot legs. Lose one leg and every circuit on that leg goes dead, which is roughly half the house. Lose or loosen the neutral and the two legs stop sharing a stable reference, so voltages swing high and low across the panel, dimming some loads and overdriving others. Reading "half the house" as a tripped breaker wastes the call and misses a fault that can damage appliances or, with an open neutral, energize things that should be dead. Translate the words to a leg-level test at the panel before touching a single branch circuit.

Symptom presentation

The customer reports that a group of rooms or circuits are completely dead while the rest work normally, often "one side of the house." Variants that point to an open neutral instead of a dead leg: lights brightening and dimming as other loads switch on and off, bulbs burning out, electronics behaving strangely, or one side dimming while the other side reads abnormally bright. The breakers are not tripped (or resetting does nothing), which is the tell that this is upstream of the branch breakers, not a branch fault.

Quick checks

• Confirm scope with the customer: a cluster of dead circuits, not one outlet, and the breakers are not tripped.
• At the panel, with the cover off and PPE on, measure leg-to-ground and leg-to-leg at the main lugs or main breaker line/load: L1-to-ground and L2-to-ground should each read about 120 V; L1-to-L2 should read about 240 V.
• A leg reading near 0 V to ground is a lost leg. Both legs present but voltages swinging or one high and one low under load points to an open neutral.
• Check the main breaker and lugs for heat, discoloration, or loose connections; check the meter and service entrance.
• Ask whether anything preceded it: a storm, a buzz or pop, flickering, or a utility event.

Isolation tree

1. One leg reads near 0 V to ground while the other reads 120 V? Lost line (open hot leg). The dead circuits are all on the missing leg. The break is at the main breaker, a main lug, the meter, the service drop, or a utility-side connection. Find where the leg goes dead by working from the main breaker back toward the meter.
2. Both legs read about 120 V to ground at rest but voltages swing wildly as loads change, one side dim and the other overbright? Open or high-resistance neutral. The neutral connection is loose or broken at the panel neutral bar, the meter, the service neutral, or the utility connection.
3. Leg-to-leg reads 240 V and both legs steady to ground? The service is intact; the dead group is a downstream feeder or a multiwire branch issue. Trace the dead circuits to a common feeder, subpanel feeder, or shared neutral that is open.
4. Heat, scorch, or a loose lug at the main breaker or neutral bar? You have found a likely break point; do not energize through a damaged lug.
5. Fault traces to the meter or the drop, ahead of your point of demarcation? It is the utility's; stop and call them.

Confirming diagnosis

For a lost leg, confirm by tracking the 0 V leg upstream: it will read 120 V at the source side of the break and 0 V on the load side. A bad main breaker pole, a burned main lug, or a failed meter jaw are the common in-panel culprits; a failed drop connection is the utility's. For an open neutral, confirm by measuring neutral-to-ground at the panel under varying load: a sound neutral stays near 0 V, while an open neutral shows voltage on the neutral that rises with imbalance, and the two legs read complementary (one high, one low) that worsens as you load one side. Wiggle-testing the neutral connections (de-energized where possible) often reveals a loose bar screw or a corroded splice.

Remediation

Match the fix to the confirmed break. Loose or burned main lug or neutral-bar screw: de-energize, clean or replace the lug/conductor, and torque to spec. Failed main breaker pole feeding a dead leg: replace the main breaker. Damaged or corroded panel neutral connections behind an open neutral: re-terminate to clean, properly torqued connections; replace damaged bus or conductor. Anything on the line side of the meter (drop, weatherhead, meter base/jaws, utility neutral): coordinate with the utility, as that is their conductor. After repair, re-measure both legs to ground (about 120 V each), leg-to-leg (about 240 V), and neutral-to-ground (near 0 V) under load to confirm a stable, balanced service before closing up.

References

• National Electrical Code (NFPA 70), Article 230, Services.
• NEC Article 250, Grounding and Bonding (grounded/neutral conductor and main bonding jumper).
• NEC Article 408, Switchboards, Switchgear, and Panelboards (busbar and terminal connections).
• NEC Article 110.14, Electrical Connections (torque and termination requirements).
• NFPA 70E, Standard for Electrical Safety in the Workplace (energized-work and PPE requirements).