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.

[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.

[WSIU940]

2 minutes ago, WRTC928 said:

That's a very good explanation. Thank you.

Thankfully my education as an industrial controls electrician helped me wrap my head around this stuff pretty well. I use to wonder why things like bonding and what not were required when I first started in the career.  I had great instructors who broke the ideas down to bite size pieces that were easy to understand and gave examples that supported the "science" of it all.