Single-Point Cable Sheath Bonding: Purpose, Limits and Design Inputs
Engineering guide: Single-point bonding interrupts the continuous sheath-current path, but it does not eliminate induced sheath voltage. The arrangement therefore requires a project-specific voltage and insulation assessment.
On this page: What the arrangement changes · The trade-off is standing voltage · Inputs the calculation needs · Protection and continuity · Lifecycle check
What the arrangement changes
One end of the metallic sheath section is bonded to earth while the other end is insulated from an earth connection for power-frequency current. This can reduce circulating-current loss compared with solid bonding.
The trade-off is standing voltage
Magnetic coupling from conductor current produces a voltage along the sheath. Its magnitude depends on cable geometry, current, section length, phase arrangement and nearby circuits. The accessible voltage and jacket stress must remain within the project criteria.
Inputs the calculation needs
Record conductor current for normal and contingency states, cable spacing and formation, sheath dimensions and resistance, section length, grounding arrangement, fault levels, joint locations and transient study basis. Generic distance rules are not a substitute for calculation.
Protection and continuity
The design may include sheath voltage limiters, insulated joints, bonding leads and link boxes selected through insulation-coordination and fault-duty studies. Their earthing and physical protection are part of the system.
Lifecycle check
CIGRE treats design, installation testing, maintenance and monitoring as one lifecycle. Keep the approved bonding diagram with cable records and verify that field links match it before energization.
Related engineering guides
Continue with the main topic guide. The design concepts here require project-specific studies, applicable standards and qualified personnel.
Next in this series: Both-End Bonding of Cable Sheaths: Circulating Current and Rating Impact · Cross-Bonding of HV Cable Sheaths: Major Sections and Transposition Logic · Sheath Voltage Limiters in HV Cable Systems: What the Design Must Prove
Sources and image credit
Technical reference: primary engineering source. Photo by American Public Power Association under the Unsplash License. Original educational content by ST College.