Principle and configurations of grounding

Principle of grounding

Grounding is providing a low-impedance path to a common reference point (earth or chassis) for return currents, fault current and noise. The principle: all circuits should have a common zero-volt reference and every current should have a defined, low-impedance return path to its source without creating common-impedance coupling between circuits. Grounding also provides safety (fault current diverts to earth so protective devices operate), and a stable reference for signals, and diverts noise and static charge.

Configurations

There are three basic grounding configurations:

1. Single-point ground: every circuit has its own ground wire, connected to one common point.
   • Series (daisy-chain) connection: simple but with common impedance coupling.
   • Parallel (star) connection: no common impedance, better, but needs more wiring. Suitable for low frequency (below 1 MHz).
2. Multi-point ground: every circuit connects to the ground plane/chassis by the shortest path. Suitable for high frequency (above 10 MHz) since lead inductance is minimised.
3. Hybrid ground: acts as single-point at low frequency and multi-point at high frequency (using capacitors/inductors) for systems containing both.

 Single-point (star)        Multi-point
  C1  C2  C3                C1   C2   C3
   \  |  /                  |    |    |
    [ point ]            ===== ground plane =====

Floating ground (isolated from earth) is sometimes listed as another configuration used to avoid ground loops.