Isolated ground
Encyclopedia
Isolated ground means the use of a local ground connection with a supply, one of the common earthing arrangements used with domestic mains supplies
.
The primary reason for the use of isolated grounds (IG) is to provide a noise-free ground return, separate from the equipment grounding (EG) return. The EG circuit includes all of the metal conduit, outlet boxes, and metal enclosures that contain the wiring and which must be grounded to provide a safe return path for any fault current that might occur. The IG's purpose is to provide an insulated, separate ground path for the ground reference in electronic equipment, such as computers, hospital equipment, and audio equipment. The use of IG helps eliminate the potential for a "ground loop", which can cause noise, data errors, and disruptions to these systems. The IG is typically insulated and separate all the way back to the point of origin of the circuit, either a main panel or sub-panel. The IG, EG and neutral are all bonded together at that point. Due to the installation of a separate, insulated conductor and the associated special outlets required, IG circuits are more expensive to install than standard power circuits.
Its main downside is its usually higher impedance than other earthing systems, resulting in slightly lower safety levels.
Until the 1950s, isolated ground domestic mains supplies tended to have no RCD
or ELCB
, and too high a ground impedance to blow a fuse if a live to earth fault occurred. This would leave large quantities of metalwork in the house live. The use of RCDs (or formerly ELCBs) with such installs solved this problem. Such installs are called EEBAD.
The British term for isolated ground is "IT", from the French terre isolee.
or an uninterruptible power supply
. If the receptacle is not installed correctly, it can create a dangerous installation.
Mains electricity
Mains is the general-purpose alternating current electric power supply. In the US, electric power is referred to by several names including household power, household electricity, powerline, domestic power, wall power, line power, AC power, city power, street power, and grid power...
.
The primary reason for the use of isolated grounds (IG) is to provide a noise-free ground return, separate from the equipment grounding (EG) return. The EG circuit includes all of the metal conduit, outlet boxes, and metal enclosures that contain the wiring and which must be grounded to provide a safe return path for any fault current that might occur. The IG's purpose is to provide an insulated, separate ground path for the ground reference in electronic equipment, such as computers, hospital equipment, and audio equipment. The use of IG helps eliminate the potential for a "ground loop", which can cause noise, data errors, and disruptions to these systems. The IG is typically insulated and separate all the way back to the point of origin of the circuit, either a main panel or sub-panel. The IG, EG and neutral are all bonded together at that point. Due to the installation of a separate, insulated conductor and the associated special outlets required, IG circuits are more expensive to install than standard power circuits.
Its main downside is its usually higher impedance than other earthing systems, resulting in slightly lower safety levels.
Until the 1950s, isolated ground domestic mains supplies tended to have no RCD
Residual-current device
A Residual Current Device is a generic term covering both RCCBs and RCBOs.A Residual-Current Circuit Breaker is an electrical wiring device that disconnects a circuit whenever it detects that the electric current is not balanced between the energized conductor and the return neutral conductor...
or ELCB
Earth leakage circuit breaker
An Earth Leakage Circuit Breaker is a safety device used in electrical installations with high earth impedance to prevent shock. It detects small stray voltages on the metal enclosures of electrical equipment, and interrupts the circuit if a dangerous votlage is detected...
, and too high a ground impedance to blow a fuse if a live to earth fault occurred. This would leave large quantities of metalwork in the house live. The use of RCDs (or formerly ELCBs) with such installs solved this problem. Such installs are called EEBAD.
The British term for isolated ground is "IT", from the French terre isolee.
Noise
An isolated ground, if installed correctly, can reduce some electrical noise. However, complete power conditioning and protection will usually require other devices such as a surge protectorSurge protector
A surge protector is an appliance designed to protect electrical devices from voltage spikes. A surge protector attempts to limit the voltage supplied to an electric device by either blocking or by shorting to ground any unwanted voltages above a safe threshold...
or an uninterruptible power supply
Uninterruptible power supply
An uninterruptible power supply, also uninterruptible power source, UPS or battery/flywheel backup, is an electrical apparatus that provides emergency power to a load when the input power source, typically mains power, fails...
. If the receptacle is not installed correctly, it can create a dangerous installation.