Stray voltage: Difference between revisions
==Terminology==
==Terminology==
{{anchor|NEV}}Stray voltage is any case of undesirable elevated electrical potential, but more precise terminology gives an indication of the source of the voltage. ”’Neutral to earth voltage (NEV)”’ specifically refers to a difference in potential between a locally grounded object and the grounded return conductor, or [[neutral and ground|neutral]], of an electrical system. The neutral is theoretically at 0 V potential, as any grounded object, but current flows on the neutral back to the source, somewhat elevating the neutral voltage. NEV is the product of current flowing on the neutral and the finite, non-zero [[electrical impedance|impedance]] of the neutral conductor between a given point and its source, often a distant substation. NEV differs from accidentally energized objects because it is an unavoidable result of normal system operation, not an accident or a fault in materials or design.
{{anchor|NEV}}Stray voltage is any case of undesirable elevated electrical potential, but more precise terminology gives an indication of the source of the voltage. ”’Neutral to earth voltage (NEV”’ specifically refers to a difference in potential between a locally grounded object and the grounded return conductor, or [[neutral and ground|neutral]], of an electrical system. The neutral is theoretically at 0 V potential, as any grounded object, but current flows on the neutral back to the source, somewhat elevating the neutral voltage. NEV is the product of current flowing on the neutral and the finite, non-zero [[electrical impedance|impedance]] of the neutral conductor between a given point and its source, often a distant substation. NEV differs from accidentally energized objects because it is an unavoidable result of normal system operation, not an accident or a fault in materials or design.
==Definitions==
==Definitions==
[[Capacitive coupling]] is the mechanism used by electrical tester pen devices. Because the capacitance between an object and a current source is typically small, only very small currents can flow from the energized source to the coupled object. [[Multimeter#Sensitivity and input impedance|High-impedance digital or analog voltmeters]] may measure elevated voltages from non-energized objects due to this coupling, in effect providing a misleading reading. For this reason, high-impedance voltage measurements of normally non-energized objects must be verified.
[[Capacitive coupling]] is the mechanism used by electrical tester pen devices. Because the capacitance between an object and a current source is typically small, only very small currents can flow from the energized source to the coupled object. [[Multimeter#Sensitivity and input impedance|High-impedance digital or analog voltmeters]] may measure elevated voltages from non-energized objects due to this coupling, in effect providing a misleading reading. For this reason, high-impedance voltage measurements of normally non-energized objects must be verified.
Verification of a voltage reading is performed using a ”low-impedance” voltmeter, which usually has a [[shunt resistor]] load bridging the voltmeter terminals. Since very little current can flow from a coupled surface through the small shunt or meter resistance, capacitively coupled voltages will collapse to zero, indicating a harmless “false alarm”. By contrast, if an object being tested is in contact with a [[current source]], or coupled by a very large capacitance (possible but unlikely in this context), the voltage will drop only slightly as dictated by [[Ohm’s Law]]. In this latter case, real power is being delivered, indicating a potentially hazardous situation.
Verification of a voltage reading is performed using a ”low-impedance” voltmeter, which usually has a [[shunt resistor]] load bridging the voltmeter terminals. Since very little current can flow from a coupled surface through the small shunt or meter resistance, capacitively coupled voltages will collapse to zero, indicating a harmless “false alarm”. By contrast, if an object being tested is in contact with a [[current source]], or coupled by a very large capacitance (possible but unlikely in this context), the voltage will drop only slightly as dictated by [[Ohm’s ]]. In this latter case, real power is being delivered, indicating a potentially hazardous situation.
Electric field detectors detect the electric field strength relative to the user’s body or mounting platform. By sensing [[electric field]] gradients at a distance, they can detect energized objects without making direct contact, making these instruments useful for scanning or screening large areas for potential electrical hazards. A low electric field reading also provides a definitive indication that no…
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