I'm trying to determine the best (safest) way to ground some new, existing (and future) antennas on our roof.
(this post could be under any forum area, amateur radio, commercial, etc), but the purposes of our antennas is actually both for commercial frequencies and the amateur radio bands).
In researching this, I find there is a lot of confusion, and differences of opinion, as well as NEC, and/or CDN electrical code that is discussed.
btw.. my understanding of NEC and CDN electrical code is (primary requirements - I know there are others):
1) all grounding systems must be bonded together
2) there should be a 6ft/2m clearance between feeder lines (ie:coax) and grounding conductors.
3) coax/line feeders must have arrestors at a point closest to where they enter a building.
To focus on the bonding part... and question... why should we bond our antenna grounding system(s) to our home electrical system grounding.
This is the logic (and my opinion) that tells me why:
(btw, while I have some electrical background, I'm no scientist
)
1) You never want high potential (especially > 1Kv)/voltage between grounding systems (because that can obviously lead to damage, fire etc).
2) The question of how do you get voltage difference between grounding systems... this is how I see it:
a) when lightning hits a specific location, the ground becomes a large resistor over hundreds, if not thousands of feet where the voltage potential between varying distances, can be deadly/damaging. One term they use, is step voltage, or step potential. If you were walking near a tree that was hit by lightning, you could theoretically be subject to thousands of volts between your legs which would/could kill you.
Lightning - People/animals:
Step voltages 1
Step voltages 2
b) so assuming the ground becomes a huge resistor that dissipates the energy over milliseconds, with different very high voltages across two points on the ground (and higher voltage across longer distances between those points), if you had a ground rod on one side of your house, and you electrical system on the opposite side, as the lightning voltage, you could end up with very high (and capable of arcing across what you may consider not very conductive materials) damaging/destructive voltages between those two grounds which would be finding conductive paths.
Therefore, if your the antenna for your radio had a separate ground, the outer sheath would ground the chassis to that antenna ground. If you had another AC system ground (unbounded to your antenna ground) from a wall receptacle also ground the same chassis, in the event of a lightning strike, this could be the point where those two grounding systems, with potentially damaging voltage meets and arcs (with obvious results). This is just one point where this damage could occur where two or more grounding systems that exist in a house or any conductive material that could experience "step voltage" or differences in voltage that can occur between two points during a lightning strike.
The same dissipation of voltages in the ground occur when a high voltage transmission line comes in contact with the earth. The ground becomes a large resistor, with almost cylindrical differences in voltage between two points as it dissipates.
Step voltages from downed transmission lines 1
Step voltages from downed transmission lines 2
When I went to college (decades ago) taking electrical courses, the instructor talked of step voltages, and mentioned that if you absolutely had to move on the ground, to hop on one foot, rather than walk or run.
To summarize, the more ground rods you set up in a given area, around your house, or for different ground systems, and bond them together, along with even other large metal surfaces, you force the ground around high voltage from a lightning strike (or nearby one), to absorb the energy, rather than your house or building.
Perhaps my posting may be disagreed on by some, I haven't seen too may articles that are not technical jargon, and simply described so most can understand it.
Btw.. my next research, is how 90 degree bends affect a grounding conductor from an antenna to a ground rod. (sometimes its hard not to have bends in it).
(this post could be under any forum area, amateur radio, commercial, etc), but the purposes of our antennas is actually both for commercial frequencies and the amateur radio bands).
In researching this, I find there is a lot of confusion, and differences of opinion, as well as NEC, and/or CDN electrical code that is discussed.
btw.. my understanding of NEC and CDN electrical code is (primary requirements - I know there are others):
1) all grounding systems must be bonded together
2) there should be a 6ft/2m clearance between feeder lines (ie:coax) and grounding conductors.
3) coax/line feeders must have arrestors at a point closest to where they enter a building.
To focus on the bonding part... and question... why should we bond our antenna grounding system(s) to our home electrical system grounding.
This is the logic (and my opinion) that tells me why:
(btw, while I have some electrical background, I'm no scientist
)1) You never want high potential (especially > 1Kv)/voltage between grounding systems (because that can obviously lead to damage, fire etc).
2) The question of how do you get voltage difference between grounding systems... this is how I see it:
a) when lightning hits a specific location, the ground becomes a large resistor over hundreds, if not thousands of feet where the voltage potential between varying distances, can be deadly/damaging. One term they use, is step voltage, or step potential. If you were walking near a tree that was hit by lightning, you could theoretically be subject to thousands of volts between your legs which would/could kill you.
Lightning - People/animals:
Step voltages 1
Step voltages 2
b) so assuming the ground becomes a huge resistor that dissipates the energy over milliseconds, with different very high voltages across two points on the ground (and higher voltage across longer distances between those points), if you had a ground rod on one side of your house, and you electrical system on the opposite side, as the lightning voltage, you could end up with very high (and capable of arcing across what you may consider not very conductive materials) damaging/destructive voltages between those two grounds which would be finding conductive paths.
Therefore, if your the antenna for your radio had a separate ground, the outer sheath would ground the chassis to that antenna ground. If you had another AC system ground (unbounded to your antenna ground) from a wall receptacle also ground the same chassis, in the event of a lightning strike, this could be the point where those two grounding systems, with potentially damaging voltage meets and arcs (with obvious results). This is just one point where this damage could occur where two or more grounding systems that exist in a house or any conductive material that could experience "step voltage" or differences in voltage that can occur between two points during a lightning strike.
The same dissipation of voltages in the ground occur when a high voltage transmission line comes in contact with the earth. The ground becomes a large resistor, with almost cylindrical differences in voltage between two points as it dissipates.
Step voltages from downed transmission lines 1
Step voltages from downed transmission lines 2
When I went to college (decades ago) taking electrical courses, the instructor talked of step voltages, and mentioned that if you absolutely had to move on the ground, to hop on one foot, rather than walk or run.
To summarize, the more ground rods you set up in a given area, around your house, or for different ground systems, and bond them together, along with even other large metal surfaces, you force the ground around high voltage from a lightning strike (or nearby one), to absorb the energy, rather than your house or building.
Perhaps my posting may be disagreed on by some, I haven't seen too may articles that are not technical jargon, and simply described so most can understand it.
Btw.. my next research, is how 90 degree bends affect a grounding conductor from an antenna to a ground rod. (sometimes its hard not to have bends in it).
