A floating ground is a reference point for

electrical potential Electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is defined as electric potential energy per unit of electric charge. More precisely, electric potential is the amount of work neede ...

in a circuit which is galvanically isolated from actual earth ground. Most electrical circuits have a ground which is electrically connected to the

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

, 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 field An electromagnetic field (also EM field) is a physical field, varying in space and time, that represents the electric and magnetic influences generated by and acting upon electric charges. The field at any point in space and time can be regarde ...

s or charge accumulation within the conductor rather than being due to the usual external

potential difference Voltage, also known as (electrical) potential difference, electric pressure, or electric tension, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge ...

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 In electrical engineering, a transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple Electrical network, circuits. A varying current in any coil of the transformer produces ...

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 the 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 equipme ...

. 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 must 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 powered. Other applications include aircraft and spacecraft, where a direct connection to Earth ground is physically impossible when in flight. Instruments with floating ground

Fourthly, a floating ground can help eliminate ground loops, which reduces the noise coupled to the system. The image on the right shows an example of such a configuration. 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 An electrical injury (electric injury) or electrical shock (electric shock) is damage sustained to the skin or internal organs on direct contact with an electric current. The injury depends on the Current density, density of the current, tissu ...

upon touching it. Live chassis TVs, also known as hot chassis, 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 Headphones are a pair of small loudspeaker drivers worn on or around the head over a user's ears. They are electroacoustic transducers, which convert an electrical signal to a corresponding sound. Headphones let a single user listen to an ...

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 with 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 ...

to make the arrangement safe. Floating grounds can cause problems with audio equipment using RCA connectors (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 can be incorporated into a system to reduce but not eliminate the risks caused by a floating ground.

References

{{Reflist Electronic circuits

Applications

Safety

See also

References