Running a ground (earth) cable beside each phase cable is an important safety & performance procedure in electrical systems.
This is why it is done:
Primary Reasons
Safety Protection
The earth cable serves as a low-resistance conduit for fault currents to return to their source.
If a phase conductor’s insulation fails and it contacts a metal enclosure (or) equipment frame the earth cable permits the fault current to swiftly trip the circuit breaker protecting anyone from being shocked by the equipment.
Voltage Stabilization
The earth connection serves in maintaining the electrical systems reference potential (zero volts) constant.
This maintains the system voltage stability and predictability which is essential for effective equipment performance.
Electromagnetic Compatibility
Connecting the earth connection to the phase cables decreases electromagnetic interference.
The fault current (or) leakage current returns via the ground wire in close proximity to the phase conductors reducing the magnetic field loop area and inductance. This is especially critical for sensitive electronic devices.
Faster Fault Clearing
When the ground cable runs parallel to the phase cables it has a lower impedance than a remote ground return connection. This enables for greater fault currents to flow causing safety devices (circuit breakers & fuses) to work more efficiently and disconnect the damaged circuit.
Equipotential Bonding
The earth cable ensures that all metal parts of an electrical installation have the same potential which prevents dangerous voltage discrepancies between various pieces of equipment or structural components.
Applications
In current installations this method is often carried out using multi-core cables that comprise both phase conductors & a protective earth conductor in the same cable assembly (or) by running separate earth cables in same conduit (or) cable tray as the phase cables.
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