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What is equipotential bonding for radio frequencies, and parallel earth conductors?

Where there are different items of equipment in different locations, with metal cables connecting them together (e.g. a variable-speed drive and its motor, a thermocouple and its remote amplifier, two servers) – electrically bond all the metal parts of their respective structures together with multiple welds, multiple screws, or multiple short (<100mmm) wide braid straps to create a meshed earth/ground structure that extends over the whole area. This is sometimes called cross-bonding.

Bonding should include metal cabinets, cable trays, ducts, trunking, conduit, ladders, gratings, plumbing, motor frames, pressure vessels, etc. Where these metal structures are supporting cables, they are called parallel earth conductors (PECs).
This is equipotential bonding for radio frequencies (the usual single-point earthing method is only capable of being equipotential up to about 5kHz, whatever the CSA of its earth wires). The highest frequency that is capable of being controlled by this method is given in MHz by the 75/L where L is the dimension of the largest mesh in the structure. So a 3m mesh size can be equipotential up to 25MHz.

The exceptions to this is when the different items of equipment only share the same electrical power supply, and the signal conductors between them are fibre-optic, or metal fieldbus cables with high noise immunity and high surge immunity (ideally at least 10kV).

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