There are five reasons for grounding your system. They are Electrical Shock Hazards, Power Faults Clearout, Lightning Hazards, Electrostatic Discharge (ESD) and Electro-magnetic Interference (EMI) Control.

Our power distribution system uses the earth ground as a reference rather than allow the power distribution to be floating. A floating system is not referenced to ground but instead has a hot and return with the return not grounded. They do this to prevent us from getting shock when we touch the equipment. If we could design a perfect floating system and we didn't conduct electricity there would not be a problem. However, the human body resistance can be as low as 1000 ohms. If you touched 115 V ac then 75 mA would flow through your body which is enough to kill (as little as 50 mA can kill a person). Thus the reason for the National Electric Code requiring grounds.

Rodents chewing on wires, old insulation, damage to wires, misconnected wires can cause power faults. These can result in electrical currents flowing in the ground and return wires over and above what the wires are supposed to carry. Since the equipment frame is grounded, this current can flow in the frame, causing a shock hazard. The energy of the fault may overheat the wire causing a fire and the burning insulation to give off toxic fumes. Provided the neutral is grounded to earth at the power source (your breaker box), any fault will appear as a short and cause the circuit breaker to trip or fuse to blow. Hence the power fault is cleared and the user alerted to a problem to be repaired before someone gets injured.

Lightning can induce currents as high as 30,000 to 100,000 A in the worst case. Hence lightning rods, aerials, and associated down conductors must be able to drain these currents to earth. Without the lightning ground excessive currents could be induced between your equipment and ground, causing shock hazards to the equipment operator. These are the reasons the lightning protection system has as low an impedance path as possible to ground.

Static charges that can build up when there is no ground can cause damages to sensitive electronic equipment, particularly the integrated circuits (IC) used in today's equipment. Voltages as high as 30,000 V can easily be obtained. Static charges can also cause fires and explosions if flammable or explosive materials are in the area. Unless you are repairing your equipment or adding new IC or circuit boards, then the manufacturer has solved the ESD problem by properly grounding the equipment. If you are doing an upgrade (for example adding a new board to your ham shack computer), then use a ground strap to discharge any unwanted static buildup.

Good grounds help prevent electromagnetic interference by grounding unwanted signals. This prevents them from being coupled into you radio as noise. For example, my laptop operates in the same frequencies as my 2 meter radio. If I am not careful when I set up my station and plug my computer into an outlet serviced by a different breaker box (hence a different ground), then I can hear my computer processing on the radio. That's why I need to tie the grounds from the various breaker boxes in our home together to prevent EMI. Another example: where I live farmers have electronic fences to keep their cattle in. When grass gets to long and brushes against these fences it causes EMI than is picked up on our satellite TV as lines across the screen. One that we traced down was from a fence 1/2 mile from my home. Manufacturers design their equipment to reduce EMI. By having a good ground system you'll be helping yourself to prevent or reduce EMI coupling into your radios, and other electronic equipment or your radio coupling into other electronic equipment.

Last updated on March 30, 2006