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.

[AdmiralCochrane]

13 minutes ago, LeoG said:

Lighting is just like tornadoes.  Destroying one while barely touching the one next door.  Could have been grounding, or just dumb luck.  People struck by lighting can survive or become crispy kritter piles of dust.

It was all about EMF and loops that absorbed it.  Any luck involved was whether the loop was tuned/angled to the wave that passed thru it.

[SteveShannon]

1 hour ago, LeoG said:

That right there should protect the radio.  But I know nothing will protect with a direct hit.  Dissipating charge should be accomplished with the wire sizes as they are.
 

That won’t protect the radio at all. Electrons don’t stop instantly and between the antenna connector and the power input there’s a lot of components that are at a different potential than the coax shield and center conductor. 

1 hour ago, LeoG said:

I'm just thinking about my situation.  The main electrical connection to all 4 bays in the building I'm in is at the opposite side of where my antenna is.  That's 170' of conductor needed to make the connection from where the cable enters the building to the bond where the electrical box is.  25'+100'+45'. 
 

Yes, it’s not cheap. 

1 hour ago, LeoG said:

And as to having a ground rod for each leg of the tower why can't the 3 or 4 legs be connected by copper wire and then go to a single ground rod?  The ground loop around the tower is doing essentially just that but just increasing the cost substantially.  And would that change between a steel tower and an aluminum tower since aluminum conducts better?

Tying all of the legs to a single ground rod requires changing the path of the discharge. Having a ground for each provides a straight path to ground, plus having more rods reduces the impedance going to the ground. In an engineered ground system such as a substation you might even see a ground mat, chemicals, and other things done to minimize the resistance and create a large bed of equal potential. 

[WRTC928]

15 hours ago, WRKC935 said:

The CB guys will tell you about their coaxes popping while they are in a glass jar and disconnected from the radio.  This is the MOST DANGEROUS situation of all. 

So, what happens if the antenna is adequately grounded and you disconnect it from the radio? I have assumed the electricity would follow the path of least resistance to the ground and the coax would be at minimal risk. Is that incorrect? 

[SteveShannon]

20 minutes ago, WRTC928 said:

So, what happens if the antenna is adequately grounded and you disconnect it from the radio? I have assumed the electricity would follow the path of least resistance to the ground and the coax would be at minimal risk. Is that incorrect? 

Less risk, but not no risk.  The coax might still be at risk. What’s the breakdown voltage for the insulation of the coax?  A long piece of coax exposed to a high voltage pulse at one end but disconnected at the other end can still be damaged.  And what about the center conductor?  It isn’t grounded unless you have done something to ground it.  Depending on the design the antenna radiator elements are not usually connected to ground.

[WRTC928]

14 hours ago, SteveShannon said:

Yes, it’s not cheap. 

200' of 4 awg copper wire is about $300 which isn't prohibitive, but if you have to add another ground rod every 8', that's going to get into some serious cash, aside from the work of driving 25 ground rods. In my case, I have to cross about 30' of asphalt. Is there any reason I can't cut a groove in the asphalt, lay the bare wire in it, and fill it with asphalt patch material? Is there any disadvantage to burying the wire where it crosses grass?

[WRTC928]

2 minutes ago, SteveShannon said:

Less risk, but not no risk.  The coax might still be at risk. What’s the breakdown voltage for the insulation of the coax?  A long piece of coax exposed to a high voltage pulse at one end but disconnected at the other end can still be damaged.  And what about the center conductor?  It isn’t grounded unless you have done something to ground it.  Depending on the design the antenna radiator elements are not usually connected to ground.

My question really is whether it's safer to leave the antenna connected to the radio or to disconnect it. I assume a direct strike may fry the coax even if it's properly grounded. I can replace an antenna and coax; it's my house and myself I'm concerned about. 

[SteveShannon]

1 minute ago, WRTC928 said:

200' of 4 awg copper wire is about $300 which isn't prohibitive, but if you have to add another ground rod every 8', that's going to get into some serious cash, aside from the work of driving 25 ground rods. In my case, I have to cross about 30' of asphalt. Is there any reason I can't cut a groove in the asphalt, lay the bare wire in it, and fill it with asphalt patch material? Is there any disadvantage to burying the wire where it crosses grass?

If you use 8’ ground rods they should be driven every 16’.  There’s no benefit from placing them every 8 feet. Code doesn’t require 4 gauge. It requires 8 awg.  I wouldn’t cut the asphalt, but I would go under it.  Burying the ground wire is fine, even preferable.

Look at this document: https://reeve.com/Documents/Articles Papers/Reeve_AntennaSystemGroundingRequirements.pdf

[SteveShannon]

Just now, WRTC928 said:

My question really is whether it's safer to leave the antenna connected to the radio or to disconnect it. I assume a direct strike may fry the coax even if it's properly grounded. I can replace an antenna and coax; it's my house and myself I'm concerned about. 

Exactly.  Best is to disconnect it before it enters the house.

[WRTC928]

6 minutes ago, SteveShannon said:

If you use 8’ ground rods they should be driven every 16’. 

Okay. For some reason, I was thinking 8'. That's still a lot of ground rods for a 200' run.

6 minutes ago, SteveShannon said:

Code doesn’t require 4 gauge. It requires 8 awg.

The code is a minimum. My thought was that for such a long run, a heavier wire might be preferable. If so, I'm okay with absorbing the extra cost.

6 minutes ago, SteveShannon said:

I wouldn’t cut the asphalt, but I would go under it.  Burying the ground wire is fine, even preferable.

I can't think of any way to go under 30' of asphalt without cutting it. 

[SteveShannon]

12 minutes ago, WRTC928 said:

Okay. For some reason, I was thinking 8'. That's still a lot of ground rods for a 200' run.

The rule of thumb is that the distance between ground rods should be twice the length of the ground rod.  Anything less results in minimal additional protection.

12 minutes ago, WRTC928 said:

The code is a minimum. My thought was that for such a long run, a heavier wire might be preferable. If so, I'm okay with absorbing the extra cost.

The wire is used for bonding, equalizing the potentials of the different ground rods, not carrying the full current of a surge.  The nearby ground system takes the brunt of the current surge. 

12 minutes ago, WRTC928 said:

I can't think of any way to go under 30' of asphalt without cutting it. 

A water jet might be able to do it, but maybe cutting the asphalt is easiest.

[LeoG]

Lest you forget that a lightning strike starts on average about 20,000 feet in the air and travels to the ground with air as an insulator.

Arguing about a couple feet is moot.

[SteveShannon]

23 minutes ago, LeoG said:

Lest you forget that a lightning strike starts on average about 20,000 feet in the air and travels to the ground with air as an insulator.

Arguing about a couple feet is moot.

You’re wrong, Leo. Air, and what’s in it, is the conductor for lightning, not an insulator. There are better conductors and better insulators but ionized air is actually a pretty good conductor.
But who’s arguing about a couple feet?

[LeoG]

16' between ground rods.  Putting a coax in a glass jar etc.  Lighting is going to do what it wants even with grounding.  The grounding is a preventative measure to take care of as good as it can.  There is no 100% it's going to follow any cable, it's the least path of resistance but because of the huge voltage potentials it can leave that path.

Certainly better to have grounded the crap out of something than nothing at all.  But it doesn't mean the lightning is going to go where you want it.

I pretty much figure a direct hit is a death strike most of the time for equipment.  Near misses is where the grounding really shines.

[WRYZ926]

I have bulkheads through the wall to bring the coax in. I also have a metal plate on each side of the wall with a piece of 1/4" 20 all thread through the wall that I use for my ground point. I have a ground rod right below the bulkheads and the all thread, plates, and lightning arrestors are all connected to that ground. That ground rod along with my masts and roof mounted antennas are all bonded to my service ground.

I disconnect the coax from the bulkheads inside the house and put caps on them. I know the caps won't be much protection but hopefully they keep any charge coming down the coax and just shooting into the room.

Nothing will protect from a direct lightning strike. All we can do is minimize the damage from near strikes. 

[WRTC928]

8 hours ago, SteveShannon said:

The rule of thumb is that the distance between ground rods should be twice the length of the ground rod.  Anything less results in minimal additional protection.

The wire is used for bonding, equalizing the potentials of the different ground rods, not carrying the full current of a surge.  The nearby ground system takes the brunt of the current surge. 

A water jet might be able to do it, but maybe cutting the asphalt is easiest.

Ah, okay. The wire isn't really carrying a current in the usual sense. Good. 8 gauge wire is a lot cheaper than 4 gauge.

[WRTC928]

7 hours ago, LeoG said:

I pretty much figure a direct hit is a death strike most of the time for equipment.  Near misses is where the grounding really shines.

That's my understanding. There's a lot of weather between a sunny day and a full-on direct lightning strike, so we want to protect against as much of it as we can.

[WSIU940]

On 6/29/2025 at 8:58 AM, WRXB215 said:

Very good explanations in this thread.

Ground because lightning.

Bond because potential.

Yes. WRKC935 hits the nail on the head on all counts. It is also important for the radio system to be bonded in case there is an electrical short between the radio system conductors like antenna cable and any hot conductors of an electrical system. The only way some breakers can sense a fault when a communications line become energized is if there is a return path back to the electrical panel that is bonded to the neutral conductor. The breaker cannot clear the fault without a return path. The earth is a poor conductor and is not an effective fault current return path. Ground fault circuit interruptors (GFCI) sense an imbalance of current on the hot and neutral conductors. If the difference is around 5 milliamps or so, the GFCI trips. This is why a GFCI doesn't need a ground wire to work. It senses when current is being drawn by other sources and that current isn't returning to the source (electrical panel). 

[WRKC935]

On 6/30/2025 at 10:21 AM, WRTC928 said:

So, what happens if the antenna is adequately grounded and you disconnect it from the radio? I have assumed the electricity would follow the path of least resistance to the ground and the coax would be at minimal risk. Is that incorrect? 

Remember that I personally work in the commercial two-way field.  Ham's and GMRS folks have the ability to disconnect their gear.  Police and fire don't.  And again, a public safety dispatch site really can't.  They need stuff up and operational all the time.  The stuff I am talking about is what gets done with their setups and what keeps them on the air. 

If you disconnect your antenna line from your radio then it's no different than leaving it connected IF everything is properly grounded and bonded.  Because the lines, tower, and equipment is all still grounded. 

Something I forgot to mention with grounding and bonding.  And the reason you bond the coax cables to the tower at the top, every 100 feet down and then at the bottom where the cable turns out of the tower and goes to the building is the magnetic pulse that happens if the tower does get hit.  Due to the extreme currents that are present during the event (strike) there is a significant magnetic field that surrounds the tower.  We all know that a wire will have a field around it as current passes through it.  It's how motors work.  Now crank that from a 6 volt battery to lightning.  EVERY conductor that's around that structure taking the hit is exposed to that field.  And remember that we pass coils of wire in magnetic fields to generate power.  Again, little DC generator hooked to a light bulb with a couple small magnets will light a light bulb when we spin the generator with our fingers.  Turn that up to lightning power and magnetic fields.  So we BOND the coax shield, since it's a conductor back to the tower to equalize that induced current and voltage and shunt it back to the tower and ultimately to ground.

There is a LOT of science to bonding and grounding of towers and antenna systems.  There are some of use that have went down that rabbit hole and have a reasonable understanding of this. 

And I will say this, keeping it simple.  Cars get hit by lightning, even though they are on rubber tires.  And the reason is that 6 inches of rubber ain't enough to keep an arc that's thousands or tens of thousands of feet in length from hitting a car with 4 inches of rubber.  And they get hit because they aren't grounded.  You ever get a bite from a car getting in or out?  It's a thing. But a glass jar isn't gonna keep that genie in the bottle any more than 4 inches of rubber is gonna keep your car from being hit.  IT has to be grounded properly or you are INVITING a strike.

 

 

[WRKC935]

On 6/28/2025 at 1:21 PM, tcp2525 said:

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

Even though this is about as far from the truth as I can imagine, I am gonna give you to benefit of the doubt to explain this, WITH links to real documentation proving what you are saying is true. 

Even if I know it's BS and in truth NOT EVEN possible.  I mean seriously, just give me a part number for the Burndy lug that's a single .25 (1/4 inch) hole that I can connect to an MTR repeater ground screw.   Let along the one for a 10-32 screw hole that would be on a radio.  Never mind getting the 500 bent into shape to connect to the radio.  I have to see this.  Do you have pictures?  Are you using the 500 cable as the method to mount the radios on a desk? 

 

[WRKC935]

On 6/28/2025 at 1:53 PM, tcp2525 said:

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

Again, where are you placing the surge suppressor's?  They typically are inside the structure, either directly mounted to or wired to a ground bar located right at the entry point.  Surge suppressors are a serviceable item, so they need to be exposed to be replaced after they fire and short.  Not wrapped in putty and tape outside.  Where do you come up with this crap? 

[WRTC928]

So, to expand on the subject a little, what about a situation where the entire system is self-contained such as a portable setup? Battery, radio, and antenna, but no connection to outside power. What does that need for grounding? Obviously, it doesn't need to be kept at the same potential as the house, since there's no house and it's not getting power from a shared system. Since you have a pole holding an antenna up in the air, does it need something for lightning protection? Is there a way or even a need to equalize potentials among the components?

[SteveShannon]

8 minutes ago, WRTC928 said:

So, to expand on the subject a little, what about a situation where the entire system is self-contained such as a portable setup? Battery, radio, and antenna, but no connection to outside power. What does that need for grounding? Obviously, it doesn't need to be kept at the same potential as the house, since there's no house and it's not getting power from a shared system. Since you have a pole holding an antenna up in the air, does it need something for lightning protection? Is there a way or even a need to equalize potentials among the components?

Portable devices typically are not grounded. 

[WRTC928]

1 hour ago, SteveShannon said:

Portable devices typically are not grounded. 

I thought that, but I just wondered if anyone thinks they should be. 

[WSIU940]

On 6/28/2025 at 12:05 PM, 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.

 

Bare with me, I will try to explain this as concisely as possible but things are about to get technical. This is by no means every reason as to why you should bond the two systems but here are a few examples.

 

Bonding creates a low-impedance path for lightning to flow to ground which in turn prevents dangerous voltage differences between different parts of a structure or different systems. Bonding reduces the risk of electrical shock to anyone who may be in contact with metal objects during a lighting strike event. Bonding can also prevent an event called a side flash. A side flash is where lighting current jumps from one conductive object to another due to the difference of electrical potential. 

So one of the reasons why you want to bond to the main electrical system ground (house ground) are to equalize the electrical potential of the radio communications system and its power source. Say there is a strike and the systems aren't bonded together. The lightning strike can jump to or cause what's called induced voltage on any conductive metal objects including piping, wiring, telecoms conductors etc. The earth actually makes for a poor conductor albeit some caveats and special circumstances such as soil composition, soil moisture content, yada yada; on a molecular level, the soil is comprised of elements with few free electrons. Free electrons allow for the movement of an electrical charge from one atom to another. The fewer the free electrons in an atom, the poorer the conductor. 

Say one system gets an induced electrical charge or there is a failure of one of the systems causing it to become energized with a charge. A charge from one system will discharge to another system that is not bonded, because that charged system wants to attempt to equalize and shed its excessive charge. Atoms want to remain in a neutral state. If an atom has too many electrons, it will dump those electrons anywhere it can, ie. another atom with fewer electrons.

In electrical systems, the electrons want to go back to the source which is the main electrical panel or wherever the system is bonded to neutral. if a piece of equipment such as a radio fails and sends line voltage into the coax cable, the earth being a poor conductor will have enough resistance to allow that coax to heat up and not trip the breaker that feeds power to the radio. This will cause a fire since the coax basically turns into a resistive load such as a heating element and so do the conductors in your walls feeding power to the radio. 

Static electrical charges can also build up causing discharges on sensitive electrical equipment. Say the wind is creating an electrical charge on your antenna and it wants a place to go. If that antenna isn't properly grounded and bonded, it will find a path through your equipment to ground and cause severe damage. Ground connections degrade over time as well. Copper and other metals tend to oxidize causing resistance in the electrical connection. If the resistance in the grounding system is greater than an alternative pathway to ground, that electrical charge will take that alternate pathway. 

 

Most if not all jurisdictions who have authority over codes and installations of electrical systems, communications systems etc. actually require these systems to be bonded together due to the safety aspect of the examples I listed above. 

[WRTC928]

3 minutes ago, WSIU940 said:

 

Bare with me, I will try to explain this as concisely as possible but things are about to get technical. This is by no means every reason as to why you should bond the two systems but here are a few examples.

 

Bonding creates a low-impedance path for lightning to flow to ground which in turn prevents dangerous voltage differences between different parts of a structure or different systems. Bonding reduces the risk of electrical shock to anyone who may be in contact with metal objects during a lighting strike event. Bonding can also prevent an event called a side flash. A side flash is where lighting current jumps from one conductive object to another due to the difference of electrical potential. 

So one of the reasons why you want to bond to the main electrical system ground (house ground) are to equalize the electrical potential of the radio communications system and its power source. Say there is a strike and the systems aren't bonded together. The lightning strike can jump to or cause what's called induced voltage on any conductive metal objects including piping, wiring, telecoms conductors etc. The earth actually makes for a poor conductor albeit some caveats and special circumstances such as soil composition, soil moisture content, yada yada; on a molecular level, the soil is comprised of elements with few free electrons. Free electrons allow for the movement of an electrical charge from one atom to another. The fewer the free electrons in an atom, the poorer the conductor. 

Say one system gets an induced electrical charge or there is a failure of one of the systems causing it to become energized with a charge. A charge from one system will discharge to another system that is not bonded, because that charged system wants to attempt to equalize and shed its excessive charge. Atoms want to remain in a neutral state. If an atom has too many electrons, it will dump those electrons anywhere it can, ie. another atom with fewer electrons.

In electrical systems, the electrons want to go back to the source which is the main electrical panel or wherever the system is bonded to neutral. if a piece of equipment such as a radio fails and sends line voltage into the coax cable, the earth being a poor conductor will have enough resistance to allow that coax to heat up and not trip the breaker that feeds power to the radio. This will cause a fire since the coax basically turns into a resistive load such as a heating element and so do the conductors in your walls feeding power to the radio. 

Static electrical charges can also build up causing discharges on sensitive electrical equipment. Say the wind is creating an electrical charge on your antenna and it wants a place to go. If that antenna isn't properly grounded and bonded, it will find a path through your equipment to ground and cause severe damage. Ground connections degrade over time as well. Copper and other metals tend to oxidize causing resistance in the electrical connection. If the resistance in the grounding system is greater than an alternative pathway to ground, that electrical charge will take that alternate pathway. 

 

Most if not all jurisdictions who have authority over codes and installations of electrical systems, communications systems etc. actually require these systems to be bonded together due to the safety aspect of the examples I listed above. 

That's a very good explanation. Thank you.