Half House Dead After Storm Decision Tree

Why this matters

"Half the house is dead" after a storm is one of the most misdiagnosed calls in residential electrical service. Techs see no power on a row of breakers, suspect a tripped main, reset everything, and walk. Two days later the homeowner reports dimming lights and burned electronics, because the real fault was a lost service-neutral and one leg of the 120/240 V split-phase was floating at line voltage. This article puts the diagnosis in the order a senior tradesperson actually walks it: utility side first (lost leg or lost neutral), then meter base, then main panel, then internal branch circuits. Skipping the utility-side check is how techs get hurt and how customers get billed for work that the utility owes them.

Symptom presentation

Customer reports approximately half the lights, outlets, and 240 V appliances do not work after a recent storm, lightning event, fallen tree on the drop, or vehicle hitting a pole. Possible variations: lights brighten and dim independently of load, refrigerator and electronics burning out, mild shock from metal appliances, a humming or buzzing service drop. Ask: storm timing, any sound or flash at the meter, any utility crew already on-site, any neighbor reports.

Quick checks before opening anything

Stand outside at the meter and look at the service drop. Visible: torn conductor, twisted splice, charred meter ring, missing neutral conductor (the bare twisted middle on triplex), tree contact, drop pulled away from the mast head. If you see ANY of this, stop and call the utility. The conductors from the transformer to the weatherhead are utility property in every U.S. jurisdiction; touching them outside an authorized de-energization is an OSHA 29 CFR 1910.269 violation and most state codes treat it as theft of service.

Inside, check the main breaker is ON. Check both 120 V legs at the main lugs with a non-contact tester first, then a meter. The next step depends on what those readings show.

Isolation tree

Step 1 - Voltage at the main lugs. Measure L1 to neutral, L2 to neutral, L1 to L2. Healthy reading: 120 / 120 / 240 (plus or minus 5 percent per ANSI C84.1). Three failure patterns drive every subsequent decision:

Pattern A - One leg reads 0 V to neutral, other leg reads 120 V to neutral, L1-L2 reads 120 V: lost utility leg upstream. The half of the panel fed by the dead leg is dark. Lights and outlets on the live leg work normally. No appliance damage in progress. Call the utility, lock the main open, document.

Pattern B - L1 to neutral reads above 130 V, L2 to neutral reads below 110 V, L1 to L2 still reads near 240 V: lost or high-resistance service neutral. This is the dangerous one. Voltages on the two legs float in proportion to the loads on each side - lights brighten under heavy 240 V appliance use, electronics fry, metal appliance frames may be near line voltage to earth. Shut off the main immediately, evacuate any appliances that came on during the event from the call list as suspect, call the utility for the drop, and put the customer on notice that surge damage may be hidden until power is restored. NEC 230.40 makes the service-entrance conductors from the weatherhead to the meter base the responsibility of the customer in most jurisdictions; the neutral splice INSIDE the weatherhead can be either party depending on local tariff.

Pattern C - Both legs read near 120 V, L1 to L2 reads near 240 V, but half the panel is still dead: the utility is healthy. Move to Step 2.

Step 2 - Continuity from main lugs to branch breakers on the dark half. Pull the cover. Look for burned bus-bar stab, melted breaker hook, evidence of a recent breaker that failed and dropped its grip on the bus. A blackened single stab usually means one breaker failed, arced, and that arcing destroyed the bus stab; replacing only the breaker will not restore reliable contact. If the bus is intact, individually rack each breaker on the dark leg and look for one that is mechanically tripped to the center position (residential breakers often look ON when they have actually tripped - you must cycle them fully OFF then ON).

Step 3 - Tandem and quad breaker scrutiny. After a storm-induced surge, a quad breaker feeding a 240 V load (water heater, range) sometimes fails internally with one half open. The branch circuit on the open half feeds nothing useful, but more importantly, in a multiwire branch circuit fed by a quad, an open half plus a remaining 240 V handle tie can leave a downstream 120 V leg energized through the 240 V load. Test each leg of the suspect quad to neutral with the breaker ON and the connected load disconnected.

Step 4 - Subpanel feeder. If the dead "half" is actually a whole subpanel, drop everything in the main and verify the subpanel feeder at the main breaker, then re-test at the subpanel main lugs. A storm-event lost neutral at the SUBPANEL feeder (rather than the service) produces exactly the same Pattern B symptoms inside the subpanel. The neutral-to-ground bond at the subpanel must NOT be made (NEC 250.142) - if you find a bonded neutral at a subpanel, that is a separate violation to correct after the immediate fault is resolved.

Confirming the diagnosis

Pattern A confirmed when utility restores the dead leg and both 120 V readings come back to 120 V. Pattern B confirmed by the utility splicing or replacing the neutral and the main-lug readings normalizing. Pattern C confirmed by replacing the failed breaker AND, if the bus stab is damaged, replacing the panel - a damaged bus stab is a fire risk that cannot be reliably repaired in the field. Document with photos before and after, and meter readings at every step.

Remediation

Pattern A and B - hand off to the utility. Do not energize anything until they confirm the drop is repaired and you re-meter at the main lugs. Pattern C with intact bus - replace the failed breaker with the panel manufacturer's listed device (UL 489 listed and tested to the specific panel family - cross-brand breakers are a separate compliance issue, see the panel selection matrix). Pattern C with damaged bus - quote a panel replacement and document the bus damage with photographs in the work order. Any pattern with suspect surge damage to electronics - the customer should file a utility damage claim under their tariff, which typically requires a licensed electrician's statement; provide that statement on company letterhead with your meter readings attached.

References

• NEC 2023 Article 230 - Services (specifically 230.40 service-entrance conductor responsibility, 230.71 disconnect)
• NEC 2023 Article 250.142 - Use of grounded conductor for grounding equipment (subpanel separation)
• ANSI C84.1-2020 - Electric Power Systems and Equipment Voltage Ratings (plus/minus 5 percent service tolerance)
• OSHA 29 CFR 1910.269 - Electric power generation, transmission, and distribution (utility-side work boundary)
• UL 489 - Molded-Case Circuit Breakers (panel-specific listing requirement)