lost neutral
A dangerous situation where the neutral wire in a split-phase power system becomes broken or disconnected, forcing all electrical current to flow directly between the two line wires and exposing loads connected between line and neutral to unstable and potentially-excessive voltages, posing a risk of equipment damage, electrical fire, or electric shock.
lost neutral: when your return path vanishes
A lost neutral occurs when the neutral conductor in a split-phase electrical distribution system becomes severed, disconnected at a breaker, or fails at a transformer or service entrance. In a standard 240-volt residential or light commercial panel, power arrives on two line conductors (phases) at 120 volts each relative to neutral. When that neutral connection breaks, the two phases no longer have a stable reference point, and current cannot return to the source through its intended path.
The immediate consequence is voltage redistribution across any loads still drawing current. If one phase is heavily loaded and the other lightly loaded, the lightly loaded phase sees voltage rise toward 240 volts, while the heavily loaded phase drops below 120 volts. Equipment rated for 120 volts can receive 200+ volts and burn out in seconds. Conversely, some devices may see dangerously low voltage. A motor or transformer on the high-voltage phase will overheat; incandescent bulbs may glow extremely bright before failing; electronic power supplies can explode.
Where it happens and why it matters
Lost neutrals typically occur at service lugs where the main neutral connects to the utility supply, at the utility transformer itself, or within individual circuits where a neutral wire has been cut, pinched, or corroded. The break is often invisible: a bad crimped lug, corrosion inside a junction box, or a wire fractured by vibration or thermal cycling. The problem escalates because the missing neutral is often not immediately obvious; the power is still there, and some devices still function, so discovery may be delayed until equipment fails or a technician probes the voltage.
Detection requires a qualified electrician with a multimeter. Voltage measurements between each line and ground (or between the two lines) will show imbalance; on a properly functioning 240-volt system, 120 volts should appear symmetrically on both phases relative to neutral and ground. If neutral is open, readings become erratic and depend on connected loads. Thermographic imaging can sometimes reveal hot spots at the failure point if the break is generating resistive heating.
Prevention relies on secure connections: tinned or soldered lugs, torque-spec bolts, regular inspection of service entrance hardware, and testing after any work involving the neutral. In industrial three-phase systems, a lost neutral is less catastrophic because loads can remain balanced across three lines, but it still creates conditions where single-phase loads (controls, lighting, offices) experience voltage swings. Proper bonding and grounding practices, along with ground-fault equipment and voltage monitors, provide defense against the worst outcomes.