Shunt (electrical)

In photovoltaics, the term is widely used to describe an unwanted short circuit between the front and back surface contacts of a solar cell, usually caused by wafer damage.

However, a direct lightning strike (such as on a radio tower antenna) will cause the shunt to arc and conduct the massive amount of electricity to ground, protecting transmitters and other equipment.

Another older form of lightning arrester employs a simple narrow spark gap, over which an arc will jump when a high voltage is present.

The term shunt is used in filter and similar circuits with a ladder topology to refer to the components connected between the line and common.

[1] Where devices are vulnerable to reverse polarity of a signal or power supply, a diode may be used to protect the circuit.

Two anti-parallel shunt diodes (one to conduct current in each direction) can be used to limit the signal flowing past them to no more than their threshold voltages, in order to protect later components from overload.

On warships, it is common to install battle short shunts across fuses for essential equipment before entering combat.

In this case, a separate shunt, a resistor of very low but accurately known resistance, is placed in parallel with a voltmeter, so that virtually all of the current to be measured will flow through the shunt (provided that the very high internal resistance of the voltmeter takes such a low portion of the current that it can be considered negligible).

Thomas-type shunts are still used as secondary standards to take very accurate current measurements, as using quantum Hall effect is a time-consuming process.

The accuracy of these types of shunts is measured in the ppm and sub-ppm scale of drift per year of set resistance.

The load is removed from a direct path to ground, which may create problems for control circuitry, result in unwanted emissions, or both.