Ground Lift on:
[Wikipedia]
[Google]
[Amazon]
In 
If all pieces of equipment are tied to a common ground reference without establishing ground loop, no current flows in the ground conductors and cable shields, and no noise is introduced into signal circuits. In applications such as
sound recording and reproduction
Sound recording and reproduction is the electrical, mechanical, electronic, or digital inscription and re-creation of sound waves, such as spoken voice, singing, instrumental music, or sound effects. The two main classes of sound recording te ...
, ground lift or earth lift is a technique used to reduce or eliminate ground-related noise
Noise is unwanted sound considered unpleasant, loud or disruptive to hearing. From a physics standpoint, there is no distinction between noise and desired sound, as both are vibrations through a medium, such as air or water. The difference arise ...
arising from ground loops in audio cables. It may also increase or decrease noise from other sources. Activating the ground lift on a particular piece of equipment opens the connection between the equipment ground and the shielding conductor of audio cables attached to the equipment, leaving those cables grounded only at their opposite end.
If all pieces of equipment are tied to a common ground reference without establishing ground loop, no current flows in the ground conductors and cable shields, and no noise is introduced into signal circuits. In applications such as sound reinforcement
A sound reinforcement system is the combination of microphones, signal processors, amplifiers, and loudspeakers in enclosures all controlled by a mixing console that makes live or pre-recorded sounds louder and may also distribute those sounds ...
for a concert, however, it is difficult to ensure all equipment shares a common ground reference.
Ground lift switch
Professional audio equipment intended for use withbalanced line
In telecommunications and professional audio, a balanced line or balanced signal pair is a circuit consisting of two conductors of the same type, both of which have equal impedances along their lengths and equal impedances to ground and to other ...
s may have a ground lift switch for the cable shield. The ground lift switch eliminates unwanted hum and buzz by interrupting the ground loops between equipment, preventing current flow along the cable shield between two devices. The switch disconnects pin 1 on the XLR jack, which is connected to the braid or foil shield in the cable and acts as the ground point of the circuit.
Ground lifts do not conform to Audio Engineering Society
The Audio Engineering Society (AES) is a professional body for engineers, scientists, other individuals with an interest or involvement in the professional audio industry. The membership largely comprises engineers developing devices or products ...
standard AES48.
Other ways of isolating the cable shield
Specially wired signal adaptors may leave the shield connection disconnected, or connected to safety ground through an RF bypass capacitor. Isolation transformers may be used to convert from balanced lines to single-ended inputs, and also to isolate the cable shield from the equipment safety ground.Safety
Removal of the safety ground connection on equipment can expose users to an increased danger of electric shock and may contradict wiring regulations.Douglas Self, ''Self on Audio 2nd edition'', Newnes, 2006 pp. 113-116 The safety ground is disconnected by an adaptor (cheater plug
A cheater plug, AC ground lifter or three-prong/two-prong adapter is an adapter that allows a NEMA connector, NEMA 5-15P Ground (electricity), grounding-type AC power plugs and sockets, plug (three prongs) to connect to a AC_power_plugs_and_sock ...
) in a power lead in which the ground conductor is deliberately disconnected, or by cutting a ground pin in the power plug. If a fault develops in any line-operated equipment, cable shields and equipment enclosures may become energized, creating an electric shock hazard. For example, the metal shell of a stage microphone or the strings of a guitar may become energized, creating a hazard to performers. British musicians Leslie Harvey
Leslie Cameron Harvey (13 September 1944 – 3 May 1972) was a Scottish guitarist in several bands of the late 1960s and early 1970s, most notably Stone the Crows. He was the brother of Alex Harvey.
Biography
Harvey was born in Govan, Gla ...
and Keith Relf
William Keith Relf (22 March 194312 May 1976) was an English musician, best known as the lead vocalist and harmonica player for rock band the Yardbirds. He then formed the band Renaissance with his sister Jane Relf, The Yardbirds ex-drummer Jim ...
were, in the 1970s, examples of this type of electrocution
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 ...
, in both cases fatal. Many other musicians have experienced electric shock due to ungrounded or improperly grounded equipment with less severe consequences.
See also
*Electromagnetic compatibility
Electromagnetic compatibility (EMC) is the ability of electrical equipment and systems to function acceptably in their electromagnetic environment, by limiting the unintentional generation, propagation and reception of electromagnetic energy whic ...
References