Floating Voltage
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Most electrical circuits have a ground which is electrically connected to the
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, hence the name "ground". The ground is said to be ''floating'' when this connection does not exist. Conductors are also described as having a floating voltage if they are not connected electrically to another non-floating (grounded) conductor. Without such a connection, voltages and current flows are induced by electromagnetic fields or charge accumulation within the conductor rather than being due to the usual external
potential difference Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to m ...
of a power source.


Applications

Electrical equipment may be designed with a floating ground for one of several reasons. One is safety. For example, a low voltage DC power supply, such as a mobile phone charger is connected to the mains through a
transformer A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...
of one type or another, and there is no direct electrical connection between the current return path on the low-voltage side and physical ground (earth). Ensuring that there is no electrical connection between mains voltage and the low-voltage plug makes it much easier to guarantee safety of the supply. It also allows the charger to safely only connect to live and neutral, which allows a two-prong plug in countries where this is relevant. Indeed, any home appliance with a two-prong plug must have a floating ground. Another application is in
electronic test equipment Electronic test equipment is used to create signals and capture responses from electronic devices under test (DUTs). In this way, the proper operation of the DUT can be proven or faults in the device can be traced. Use of electronic test equipmen ...
. Suppose you wish to measure a 0.5 V potential difference between two wires that are both approximately 100 V above Earth ground. If your measuring device has to connect to Earth, some of its electronic components will have to deal with a 100 V potential difference across their terminals. If the whole device floats, then its electronics will only see the 0.5 V difference, allowing more delicate components to be used which can make more precise measurements. Such devices are often
battery Battery most often refers to: * Electric battery, a device that provides electrical power * Battery (crime), a crime involving unlawful physical contact Battery may also refer to: Energy source *Automotive battery, a device to provide power t ...
powered. Other applications include aircraft and spacecraft, where a direct connection to Earth ground is physically impossible when in flight. Fourthly, a floating ground can help eliminate ground loops, which reduces the noise coupled to the system. An example of such a configuration is shown in the image on the right. Systems isolated in this manner can and do drift in potential and if the transformer is capable of supplying much power, they can be dangerous. This is particularly likely if the floated system is near high voltage power lines. To reduce the danger of electric shocks, the chassis of the instruments are usually connected separately to Earth ground.


Safety

Floating grounds can be dangerous if they are caused by failure to properly ground equipment that was designed to require grounding, because the chassis can be at a very different
potential Potential generally refers to a currently unrealized ability. The term is used in a wide variety of fields, from physics to the social sciences to indicate things that are in a state where they are able to change in ways ranging from the simple r ...
from that of any nearby organisms, who then get an electric shock upon touching it. Live chassis TVs, where the set's ground is derived by rectifying live mains, were common until the 1990s. Exposed live grounds are dangerous. They are live, and can
electrocute Electrocution is death or severe injury caused by electric shock from electric current passing through the body. The word is derived from "electro" and "execution", but it is also used for accidental death. The term "electrocution" was coined ...
end users if touched. Headphone sockets fitted by end users to live chassis TVs are especially dangerous, as not only are they often live, but any electrical shock will pass through the user’s head. Sets that have both a headphone socket and a live chassis use an audio
isolation transformer An isolation transformer is a transformer used to transfer electrical power from a source of alternating current (AC) power to some equipment or device while isolating the powered device from the power source, usually for safety reasons or to re ...
to make the arrangement safe. Floating grounds can cause problems with audio equipment using
RCA connectors The RCA connector is a type of electrical connector commonly used to carry audio and video signals. The name ''RCA'' derives from the company Radio Corporation of America, which introduced the design in the 1930s. The connectors male plug an ...
(also called phono connectors). With these common connectors, the signal pin connects before the ground, and 2 pieces of equipment can have a greater difference between their grounds than it takes to saturate the audio input. As a result, plugging or unplugging while powered up can result in very loud noises in speakers. If the ground voltage difference is small, it tends to only cause hum and clicks. A
residual current device A residual-current device (RCD), residual-current circuit breaker (RCCB) or ground fault circuit interrupter (GFCI) is an electrical safety device that quickly breaks an electrical circuit with leakage current to ground. It is to protect equip ...
can be incorporated into a system to reduce but not eliminate the risks caused by a floating ground.


See also

* Chassis ground *
Floating-gate MOSFET The floating-gate MOSFET (FGMOS), also known as a floating-gate MOS transistor or floating-gate transistor, is a type of metal–oxide–semiconductor field-effect transistor (MOSFET) where the gate is electrically isolated, creating a floating no ...
*
Cheater plug A cheater plug, AC ground lifter or three-prong/two-prong adapter is an adapter that allows a NEMA 5-15P grounding-type plug (three prongs) to connect to a NEMA 1-15R non-grounding receptacle (two slots). They are needed to allow applian ...


References

{{Reflist Electronic circuits