page_title: Stray voltage
section_title: Coupled voltages
hierarchical_section_title: Stray voltage / Causes / Coupled voltages
caption_attribution_description: English: Fluorescent tube glowing in the electromagnetic field under high voltage power transmission lines, so called "navigated voltage" which you can see near HV lines. The fluorescent lamp shown here is 8 ft (2400 mm) long. Русский: Свечение ЛДС под действием т.н. "наведённого напряжения" вблизи высоковольтных линий электропередач.
context_page_description: Stray voltage is the occurrence of electrical potential between two objects that ideally should not have any voltage difference between them. Small voltages often exist between two grounded objects in separate locations, due to normal current flow in the power system. Large voltages can appear on the enclosures of electrical equipment due to a fault in the electrical power system, such as a failure of insulation.
context_section_description: Ungrounded metal objects close to electric field sources such as neon signs or conductors carrying alternating currents can have measurable voltage levels caused by capacitive coupling.  Since voltages detected by high-impedance instruments disappear or become greatly reduced when a low impedance is substituted, the effect is sometimes called  phantom voltage (or ghost voltage). The term is often used by electricians, and might be seen, for example, when measuring the voltage at a lighting fixture after removing the bulb.  It is not unusual to measure phantom voltages of 50–90 volts when testing the wiring of ordinary 120 V circuits with a high-impedance instrument. While the voltage produced may read almost to the full supply voltage, the capacitance or mutual inductance between the wires of building wiring systems is typically quite low and incapable of supplying significant amounts of current.
  However, in overhead transmission work on or near high-voltage lines, safety rules require connecting a conductor to earth ground during maintenance, since induced voltages and currents on a conductor may be sufficient to cause electrocution or serious injury.
caption: The very small capacitance between overhead lines and a fluorescent lamp tube (in the foreground of the photo) provides enough current to cause the lamp to glow.
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