Grounding Cables Flashcards
What is the main function of a ground in electrical systems?
To provide a common voltage reference, ensure safety, and offer a return path for fault currents and surges.
What is essential to ground in medium/high voltage shielded cables?
The cable’s metallic shield.
What’s the minimum grounding requirement for shielded cables?
At least one ground point.
Where are cables commonly grounded?
At access points like manholes, cabinets, and pole-mount locations.
What do cable accessory kits usually include regarding grounding?
Instructions and materials to ground the metallic shield.
What should ground wire sizing be based on?
The current-carrying capacity of the cable’s metallic shield
What is the traditional ground wire size used if not specified
6 AWG solid copper or equivalent copper braid.
What must be done to ground braid to prevent moisture intrusion?
It must be blocked, typically solder-blocked.
Why should ground conductors be kept short?
To minimize voltage drop during fault conditions.
What’s the tradeoff in ground conductor length?
Short for minimal voltage drop, long enough for clearance
Why use single-point grounding?
To prevent induced shield (circulating) currents.
What is a risk of single-point grounding?
Full fault current passes one path; failure can cause dangerous voltages.
Why is single-point grounding limited to short runs?
Voltage drop becomes significant with longer distances.
What does double-end grounding allow?
Divides fault current between two paths, but allows shield currents
What is a shield break?
A disruption of longitudinal shield continuity while maintaining radial shielding.
Why are shield breaks used?
To enable single-point grounding over long cable runs.
How is a shield break created?
By overlapping and insulating shield ends.
What is cross bonding?
Shield breaks are connected to adjacent phases to neutralize shield currents.
What precaution is needed in cross bonding?
Use insulated jumpers due to high shield voltage.
Where is cross bonding commonly used?
In applications like wind farms for electric power regulation
What issue arose with early concentric neutral cables?
Corrosion of neutrals due to acidic/alkaline soils.
How was corrosion prevented in modern cables?
By adding an outer jacket over neutral wires.
What problem did jacketed concentric neutral cables create?
Loss of earth contact, resulting in shield voltage build-up.
What is the RUS grounding rule for jacketed cable?
Four grounds per mile, or every 1,320 feet (quarter mile).
