Question re: grounding for lightning protection

[WRTC928]

What is the logic behind bonding your lightning ground to the house ground? Lightning always wants to go to the earth, so grounding your antenna and coax makes sense. You give the lightning an easy path to the earth, and hopefully it will take it. I also understand why it's recommended that you bond the common ground for your equipment to the house ground. The powered equipment is part of the same circuit as all the other electrical equipment in the house and you want to keep it at the same potential. However, I don't follow the reasoning of bonding the two together. It seems to me that the most logical solution for protecting against lightning is to give the electrical buildup a way to get to the earth without directing it into your house; i.e., a lightning ground separate from the equipment ground. Yet everything I read recommends bonding the lightning ground to the house ground, so there must be some reason that I don't understand.

[SteveShannon]

49 minutes ago, WRTC928 said:

How does it change the calculations if the antenna is mounted on something non-conductive like a fiberglass mast? 

Obviously you don’t ground a fiberglass mast, but your coax shield is attached to part of the antenna somewhere and it will develop a charge as air currents pass over it.
Now the difference in potentials is between the metal parts of the antenna connected to the shield of the coax and the service ground, again going through your equipment and possibly you. One of the purposes of a surge suppressor (commonly called a lightning protector but nobody guarantees that) is to allow you to bond the coax shield to the grounding system. 

[tcp2525]

14 minutes ago, WRTC928 said:

What is the logic behind bonding your lightning ground to the house ground? Lightning always wants to go to the earth, so grounding your antenna and coax makes sense. You give the lightning an easy path to the earth, and hopefully it will take it. I also understand why it's recommended that you bond the common ground for your equipment to the house ground. The powered equipment is part of the same circuit as all the other electrical equipment in the house and you want to keep it at the same potential. However, I don't follow the reasoning of bonding the two together. It seems to me that the most logical solution for protecting against lightning is to give the electrical buildup a way to get to the earth without directing it into your house; i.e., a lightning ground separate from the equipment ground. Yet everything I read recommends bonding the lightning ground to the house ground, so there must be some reason that I don't understand.

All radio related grounding should be done with 500MCM cable. End of story.

[WRTC928]

22 minutes ago, tcp2525 said:

All radio related grounding should be done with 500MCM cable. End of story.

I'm sorry, but I don't understand how that relates to my question. Please elaborate.

[tcp2525]

7 minutes ago, WRTC928 said:

I'm sorry, but I don't understand how that relates to my question. Please elaborate.

You answered your own question by keeping PROPER grounding outside so there's no need to do any grounding inside the house.

[WRXL702]

It's Called Single Point Grounding.

Reason - To Eliminate A Potential Difference Between Having (2) Separate Grounding Systems.

Single Point Grounding Is Done On All Commercial Tower Sites.

[UncleYoda]

The actual ground (i.e., dirt) can be a conductor of lightning that hits nearby, especially wet ground in a thunderstorm.  By installing grounding wires, you may be increasing potential of that getting to your electronic devices inside.  For ordinary folks, disconnecting the devices from the AC and antenna lines is the best option.

[WRTC928]

2 hours ago, WRXL702 said:

It's Called Single Point Grounding.

Reason - To Eliminate A Potential Difference Between Having (2) Separate Grounding Systems.

Single Point Grounding Is Done On All Commercial Tower Sites.

Yes, but commercial tower sites don't then bond the ground to a house ground. What I'm trying to figure out is why almost every article or video I find recommends doing that.

[WRTC928]

2 hours ago, UncleYoda said:

The actual ground (i.e., dirt) can be a conductor of lightning that hits nearby, especially wet ground in a thunderstorm.  By installing grounding wires, you may be increasing potential of that getting to your electronic devices inside.  For ordinary folks, disconnecting the devices from the AC and antenna lines is the best option.

That was my logic, hence my confusion at the recommendation to do that.

[WRXL702]

32 minutes ago, WRTC928 said:

Yes, but commercial tower sites don't then bond the ground to a house ground. What I'm trying to figure out is why almost every article or video I find recommends doing that.

Correct - Because Commercial Sites Don't Have A House - They Have A Structure Or A Cabinet For Equipment.

The Structure Or Cabinet Requires Proper Bonding - For Single Point Grounding - To Avoid A Ground Potential Difference. 

[nokones]

4 hours ago, WRTC928 said:

What is the logic behind bonding your lightning ground to the house ground? Lightning always wants to go to the earth, so grounding your antenna and coax makes sense. You give the lightning an easy path to the earth, and hopefully it will take it. I also understand why it's recommended that you bond the common ground for your equipment to the house ground. The powered equipment is part of the same circuit as all the other electrical equipment in the house and you want to keep it at the same potential. However, I don't follow the reasoning of bonding the two together. It seems to me that the most logical solution for protecting against lightning is to give the electrical buildup a way to get to the earth without directing it into your house; i.e., a lightning ground separate from the equipment ground. Yet everything I read recommends bonding the lightning ground to the house ground, so there must be some reason that I don't understand.

To prevent electrical noise being transferred from one system into the other system. You are drawing power from one electrical system thus you should be using only one grounding system. If you have two earth grounding points then you have two grounding systems and that will cause problems.

[WRTC928]

43 minutes ago, nokones said:

To prevent electrical noise being transferred from one system into the other system. You are drawing power from one electrical system thus you should be using only one grounding system. If you have two earth grounding points then you have two grounding systems and that will cause problems.

I'm not following you. What does that have to do with lightning protection? What kinds of problems will it cause?

To be clear, I'm not being confrontational. I'm really trying to understand this.

[AdmiralCochrane]

So, a home antenna tower shouldn't have it's own ground? Just bond to house ground?

[SteveShannon]

Let’s disregard lightning protection for a few minutes and just talk about bonding to your house service ground. 
Your tower is sort of grounded. We all agree with that I think. It’s embedded in an imperfect conductor, concrete, at the bottom. To improve the grounding a ground wire runs from each leg of the tower to a ground rod. But any two separate ground rods are almost always at different potentials. Whenever you have different potentials between two points in a circuit you will have electric currents flowing from one point to the other. So, the three or four legs of the tower are bonded together using a material that is more conductive than the tower itself. Otherwise you have current flowing between the legs of your  tower. If current flows between the legs of your tower over time the metal of the tower will corrode. Bonding between the three or four legs provides an easier path for the current to flow which keeps the legs all at the same potential. 

In addition your antenna mount is certainly connected electrically to your tower and your coax shield is connected to your antenna mount. Your coax shield then runs to your radio. If you have a watt meter, amplifier, or any other device between your radio and your antenna, they are all connected serially via the coax shield. Their metal cases are all connected to the coax shield. So all of the devices in your shack are connected together via the coax shield. If a power surge comes through the shield (static, lightning, unicorn farts, whatever) it is going to cause current to flow through your equipment because that’s the most direct path. By bonding the chassis of all those devices to a single point, we provide a much better path that doesn’t flow through those devices. So that’s why we use a single point ground. But remember, that single point ground is connected to ground at the tower.  

You power your radio with a power supply that’s plugged into your house power. Its case is connected to the ground wire in the outlet which runs back to the service panel where it’s bonded to the service ground for the utility power coming into your house. It has to be because NEC says so. 

So let’s say you don’t have your single point ground bonded to your service ground. You reach out to touch your radio and at the same time your brush your other hand on the power supply. The potential of your tower ground, which is what your one hand is touching, is probably different than the potential of the service ground, which is what your other hand is feeling. And it’s DC. Your heart can be stopped by as little as 1/10 of an ampere. So you die. 
So we bond the tower ground to the utility ground to ensure they are at the same potential and save your life. 
Also with fewer ground currents in the shack we hear less noise. 

[WRYZ926]

18 minutes ago, AdmiralCochrane said:

So, a home antenna tower shouldn't have it's own ground? Just bond to house ground?

Unless I misread the NEC and other sources, the tower should have its own ground and be bonded to the service ground.

 

2 hours ago, WRXL702 said:

The Structure Or Cabinet Requires Proper Bonding - For Single Point Grounding - To Avoid A Ground Potential Difference. 

This is correct. 

Steve did a good job of expelling things

[WRTC928]

30 minutes ago, SteveShannon said:

In addition your antenna mount is certainly connected electrically to your tower and your coax shield is connected to your antenna mount. Your coax shield then runs to your radio.

How does it change the calculations if the antenna is mounted on something non-conductive like a fiberglass mast? 

[WRYZ926]

5 minutes ago, WRTC928 said:

How does it change the calculations if the antenna is mounted on something non-conductive like a fiberglass mast? 

It's no different than using a chimney mount or a satellite dish mount on your roof. You run the proper sized ground wire from the antenna/mount to ground.

Look at a properly installed satellite dish antenna. There will be a ground wire running with the coax. And that ground wire should be bonded to your service ground before the coax enters the structure. The same goes for cable TV, there will be a ground wire coming off the feed  to your home and it to will be grounded to the service ground when installed correctly.

[WRKC935]

To explain it really simple. 

If you have a ground rod on one end of your house for your service and another one at the other end of the house with your radio gear and they are not bonded together.  If you have a strike, even a ground strike at one end of the house, a tree near the house, or whatever at that end.  The lightning will COME IN the one ground, go through your equipment via the safety ground (bottom pin on power cord) across the equipment / power supply, into the radio then back out to the coax or ground wire, then out to the ground rod it's all hooked to.  That is the difference of potential that is talked about.  The ground is NOT a perfect conductor.  And it's not unreasonable to see 50 Kv or more across 10 feet of ground during a strike.

I install public safety radio sites, including ones that are co-located dispatch centers with radio towers.  Key part of this is the dispatchers wear headsets that as far as lightning goes, a direct path exists between the top of that tower and their headsets.

You BOND everything.  The headset jack gets bonded, the furniture, the equipment, the racks the equipment is in, the radios, the wiring between the radios and the console electronics, the coaxes entering the building with a surge suppressor, then outside the building, at the base of the tower, every 100 foot up the tower and then right at the connection point to the antenna.  The tower gets bonded to all this.  Then there are ground rods on every leg of the tower.  Those are bonded together, called a tower ground loop.  Then the building has a ring around it with ground rods every ten feet again in a loop.  Those rings are bonded together, there are lines that go out into the property with more ground rods that are every 10 feet.  All the connections are done with CadWeld or 15 ton compression connections with a hydraulic press. 

All that is bonded to the service entrance ground. 

Then in the building, everything that is metal that is a fixture gets grounded.  Meaning file cabinets, conduits, desks, window and door frames.  Anything that not immediately movable.  Of course, air handlers, plumbing, and the like are also bonded back to the ground along with the building frame if it's conductive. 

A lot of people will question the required wire gauge, stating that a number 2 wire could never hold the current of a direct strike.  And that's only partly true.  Lightning is very fast.  Wire will carry a very high amount of current for a very short amount of time.  Anyone that's ever shorted something across a battery will recognize that whatever it was didn't instantly turn to plasma and vanish.  It takes some time for the wire to heat up and then catch fire.  And longer for it to burn in half.  It's that fact that allows a number 2 conductor to take the abuse of being hit across and not just being vaporized. 

Yes, there are instances that heavier wire is needed.  Like the ground rings, runs longer than 50 feet and situations where a multipoint grounding bar is located where a number of devices are connected to a single point with number 6 wires.  But a number 6 wire, at least with the R56 install standard, is the minimum required wire gauge for any ground and if it's connected to a ground bar with other devices or grounded objects, then the wire going from that ground bar back the the master / main ground bar needs to be a number 2.

OH, and what you are referring to as a 'house ground' is the electrical service ground.  And at a tower site it IS bonded to the site grounding system.

Google the R56 standard and read over the site grounding requirements for a tower site.

 

[WRTC928]

9 hours ago, WRKC935 said:

To explain it really simple. 

If you have a ground rod on one end of your house for your service and another one at the other end of the house with your radio gear and they are not bonded together.  If you have a strike, even a ground strike at one end of the house, a tree near the house, or whatever at that end.  The lightning will COME IN the one ground, go through your equipment via the safety ground (bottom pin on power cord) across the equipment / power supply, into the radio then back out to the coax or ground wire, then out to the ground rod it's all hooked to.  That is the difference of potential that is talked about.  The ground is NOT a perfect conductor.  And it's not unreasonable to see 50 Kv or more across 10 feet of ground during a strike.

I install public safety radio sites, including ones that are co-located dispatch centers with radio towers.  Key part of this is the dispatchers wear headsets that as far as lightning goes, a direct path exists between the top of that tower and their headsets.

You BOND everything.  The headset jack gets bonded, the furniture, the equipment, the racks the equipment is in, the radios, the wiring between the radios and the console electronics, the coaxes entering the building with a surge suppressor, then outside the building, at the base of the tower, every 100 foot up the tower and then right at the connection point to the antenna.  The tower gets bonded to all this.  Then there are ground rods on every leg of the tower.  Those are bonded together, called a tower ground loop.  Then the building has a ring around it with ground rods every ten feet again in a loop.  Those rings are bonded together, there are lines that go out into the property with more ground rods that are every 10 feet.  All the connections are done with CadWeld or 15 ton compression connections with a hydraulic press. 

All that is bonded to the service entrance ground. 

Then in the building, everything that is metal that is a fixture gets grounded.  Meaning file cabinets, conduits, desks, window and door frames.  Anything that not immediately movable.  Of course, air handlers, plumbing, and the like are also bonded back to the ground along with the building frame if it's conductive. 

 

[WRTC928]

9 hours ago, WRKC935 said:

To explain it really simple. 

If you have a ground rod on one end of your house for your service and another one at the other end of the house with your radio gear and they are not bonded together.  If you have a strike, even a ground strike at one end of the house, a tree near the house, or whatever at that end.  The lightning will COME IN the one ground, go through your equipment via the safety ground (bottom pin on power cord) across the equipment / power supply, into the radio then back out to the coax or ground wire, then out to the ground rod it's all hooked to.  That is the difference of potential that is talked about.  The ground is NOT a perfect conductor.  And it's not unreasonable to see 50 Kv or more across 10 feet of ground during a strike.

Okay, now it makes sense. 

[WRXB215]

Very good explanations in this thread.

Ground because lightning.

Bond because potential.