View Single Post
Old 23-Jul-2019, 4:47 AM   #24
GroundUrMast
Moderator
 
GroundUrMast's Avatar
 
Join Date: Oct 2010
Location: Greater Seattle Area
Posts: 4,750
OTAFAN, Thanks for inviting more discussion about this...

Electrical potential is simply the voltage difference between two objects or points in an electrical circuit.

The purpose of grounding is to provide a conductive path for current between the ‘grounded’ object and earth. In the early history of electrical distribution systems, grounding was not common. As a result, those early systems experienced problems with static build up and so would experience insulation break-down and the subsequent damage to distribution equipment and/or customer equipment when the static voltage rose too high. By connecting one of the distribution conductors to earth, the voltage difference can not rise to damaging levels on the rest of the system. An antenna system would be at similar risk if it's not grounded. The modern day electrical distribution systems in most parts of North America use the multi-grounded-neutral method which has a connection to earth at most if not every distribution station, pole, transformer and customer service entrance. This assures that even if there is a poor connection to earth at one or even many points in the system, overall, the system neutral conductor has a very low resistance (impedance) connection to the earth. As a result, there is very high confidence that static build up and the damaging effects of it can be prevented.

Bonding is not the same thing as grounding and grounding is not the same thing as bonding. However, they work together to reduce hazards. Bonding is simply connecting two or more conductive items with a conductor that has low resistance and that can safely carry current if one of the objects becomes energized through some fault or accident. If the source of fault current is from a circuit conductor, you would want the use a bonding conductor that could safely carry the current until the circuit breaker trips. This serves two purposes during the fault… First, the voltage difference between all the items bonded together remains very close to zero so if you were touching two bonded items during the fault, you wont experience a shock. Two, the fault condition generates enough current flow so as to ensure the breaker will trip and thereby disconnect what would have been a hazardous voltage on the item had it not been bonded.

The earth is a rather poor (high resistance) conductor in many areas. Here in the Northwest, we commonly encounter glacial-till (the deposits left by glaciers grinding mountains into sand and gravel). My property is pretty much glacial-till with a small amount of clay. The last time I drove a ground rod here, I applied 120 AC to it (before connecting it to any part of my existing electrical service) and then measured the current… and calculated the resistance of the rod. As I expected, that 5/8ths inch by 8 foot copper clad rod had about 1500 ohms of resistance. Pretty typical for this part of the country. That means that I would have to apply 1500 volts to that ground rod in order to make one amp of current flow. The method I used is dangerous and anyone attempting to duplicate some or all of the test just described could suffer serious injury or death.

If I were to rely on a ground rod with any significant resistance to protect my antenna system I would almost always have confidence that I was protected from static build up on the antenna system. Great… But if a nail of screw happened to be driven through a a power cable and my coax, the 120 volts shorted to my coax would not be able to force enough current into the earth to cause a fuse or circuit breaker to open… I could have 120 volts standing on the exposed part of my antenna system, including the TV connected to it. That would be an obvious shock hazard and it could remain there for an indefinite period of time.

By bonding my antenna system to the electrical service grounding system (which in turn bonds to the rest of the electrical system on my property), I can have high confidence that damaged Christmas lights or errant nails and screws can’t apply hazardous voltage to my antenna system.

For what it's worth, in my work over the years, I have encountered improperly boned/grounded systems in homes and businesses. One was a dentists office where an outlet receptacle had an open circuit neutral inside... rather than replace it, someone had connected the downstream receptacles to the the conduit in order to return circuit current to the panel. I found out when I was holding onto both sides of a loose conduit connection. Current traveled through both arms and my chest. I've also come across appliances that were wet inside and as a result, had enough leakage current through the wet insulation to make me 'wakeup'. Both examples demonstrated the danger of improper bond/ground connections. I would not have been shocked if the appliance ground had not been defeated or the conduit had not been used as a circuit conductor.
__________________
If the well is dry and you don't see rain on the horizon, you'll need to dig the hole deeper. (If the antenna can't get the job done, an amp won't fix it.)

(Please direct account activation inquiries to 'admin')

Last edited by GroundUrMast; 11-Aug-2019 at 12:52 AM. Reason: Safety Warning
GroundUrMast is offline   Reply With Quote