The phantom voltage or stray voltage can cause issues like detecting voltage even the switch is off.
What Causes Voltage to Be Present When the Switch is Turned Off?
You might notice that your multimeter is detecting voltage even though the switch is off. Due to stray voltage, it’s capacitively coupled causing a voltage reading on a digital meter. But the ghost voltage can not power a load. So why is it that your voltmeter can detect it?
A standard multimeter or voltmeter is designed to provide as much impedance to current flow as possible. The intent is so that you can get a measurement while affecting the circuit as little as possible. This high impedance means that your meter won’t bleed off the ghost voltage, instead reading it as some funny-looking number of volts.
- Firstly, it might be the fault of phantom voltage or stray voltage, or ghost voltage.
- Otherwise, the switch can be faulty and not do its job correctly. Or it switches to neutral instead of breaking the circuit. This is an electrical hazard because it still keeps the hot wire active.
- Next, very often that little voltage between neutral wire and earth gets detected by a multimeter. This is a very trivial issue. Don’t worry about it.
- Then, it is possible for the switch to be shorted and lose voltage control of the outlets.
- Also, the faulty connection of the neutral wire to the ground may show extra voltage after being switched off.
- Finally, there can be a high-value filter capacitor installed at the source outlet for protection purposes. If the capacitor is not completely discharged, the stored charge shows up for a few seconds. Then the resultant capacitance may show some voltage after being powered off.
Although there are many reasons why you find voltage on an open outlet, phantom voltage is the most common & basic one of them.
Why Is There a Current When the Switch Is Off?
A very common chance is that the switch is set on the neutral wire of the circuit with a grounding fault between the switch & the voltage source. So even when the switch is off, current flows from the hot wire to the switch, then into the direct high ohm faulty ground. Think of a water tap. When you abruptly close a full-force water tap, the water stops instantly leaving a huge pressure in the system for milliseconds.
Another big reason is electromagnetic induction voltage. When current passes through a regular circuit due to voltage drop, an electromagnetic field occurs. The increasing current increases the magnetic field. Soon, the increment of this magnetic field creates a voltage that counters the applied voltage & nullifies itself eventually. The increasing current also slows down.
This whole process works in reverse after switching off the electric source. Now, the induced magnetic voltage keeps running the current through the circuit. That’s why you can still find current when switched off. But this current only exists for a few seconds.
What Causes Ghost Voltage?
Ghost voltage or stray voltage is a temporary and sourceless voltage between two points detected by a multimeter even if the switch is off. One of the reasons behind this might be the existence of stray capacitance in the circuit.
When circuits with source voltage and dead wires are close in distance or in the same circuit, then capacitive coupling occurs between the energized wire and the dead wire. Thus, ghost voltage appears on the non-energized wires. On top of that, any electric field near or around the circuit contributes to creating unwanted voltages.
Electromagnetic induction is another source of ghost voltage. Current flowing through a conductor generates a magnetic field which eventually produces a voltage in another non-energized conductor. This induced voltage rests still until a neutral wire clears it out. Insulation leakage and poor earthing might also be the causes behind this situation.
Is Phantom Voltage a Problem?
Phantom voltage has very little value of capacitance. It is unable to generate a load, furthermore, hardly impacts a functional circuit. That’s why the phantom voltage can not potentially cause any harm to a human being. However, barn animals especially dairy cows are hypersensitive to phantom voltage.
The abundance of phantom voltage on a dairy farm decreases milk production. Farmers have observed breeding and calving issues over the years due to phantom voltage.
In addition, make sure to check if it is really a phantom voltage initiated by the incorrect use of high-impedance multimeters. Any kind of electrical installation blunder mistaken as phantom voltage may lead to a shock hazard.
Why Does My Neutral Wire Have Voltage?
We measure the rest of the voltage drops in the circuit relative to the neutral. That’s why the neutral wire has zero volts. Normally, neutral wires have a negligible amount of voltage.
But in some cases, the voltages appear to be comparatively higher. Probably because the neutral wire might not be correctly grounded to the Earth.
Another reason could be neutral wire might deliver back some current from the hot to its line through the other load. Your voltmeter is identifying this voltage without showing the other load’s existence. Try disconnecting the other voltage sources, and check if the neutral voltage becomes null.
Faulty wiring and open grounds are also some other reasons to display neutral voltage.
To Conclude
There is very little energy transferred in the phantom voltage. So, it’s usually not dangerous because it can produce almost no current. However, it can cause confusion and confusion can lead to dangerous mistakes. Most voltage testers and multimeters are useless for telling the difference between real and phantom voltages.
Leave a Reply