Question E0A01:
What is the primary function of an external earth connection or ground rod?  

Choices:  
A: Prevent static build up on power lines  
B: Lightning charge dissipation  
C: Reduce RF current flow between pieces of equipment  
D: Protect breaker panel from power surges    

Correct Answer is  B: Lightning charge dissipation  

Primary function: Provide a low-impedance path to earth so lightning and static charge on antennas/towers can be safely bled off and diverted away from equipment and people. Hence, Lightning charge dissipation is correct.

Why the correct answer is correct
- An external earth connection (ground rod) gives lightning and static a direct path to earth, reducing the chance that surge energy will enter the shack or equipment via feedlines or AC wiring.

Why the other choices are incorrect
- A: Prevent static build up on power lines — Utilities handle power-line grounding; your station’s ground rod does not control static on the utility distribution system.
- C: Reduce RF current flow between pieces of equipment — Inter-equipment RF issues are addressed by bonding equipment to a single-point ground bus and using ferrites/chokes. A ground rod is often inductive at RF and is not effective for controlling RF currents between gear.
- D: Protect breaker panel from power surges — Surge protective devices (SPDs) at the service entrance do this. While the grounding electrode system is required and helps provide a reference, the ground rod itself is not the primary surge protector.

Useful formulas and rules of thumb
- Lightning is a fast-rising surge; inductance in the down conductor creates voltage:  
  $$V = L \,\frac{di}{dt}$$  
  Keep ground conductors short, straight, and wide to minimize $L$.
- At RF, a “ground wire” can be inductive and ineffective:  
  $$X_L = 2\pi f L$$  
  Don’t rely on an earth rod for RF returns; use bonding, proper feedline chokes, and a single-point ground.
- Bond all grounds together (station ground to AC service ground) to avoid dangerous potential differences.
- If needed to lower ground resistance, use multiple rods spaced at least one rod length apart and interconnect with heavy bonding strap.