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.

[LeoG]

9 minutes ago, AdmiralCochrane said:

Disconnect/open loops because EMF.

 

 

Lightning strike between my house and neighbor's house took out 2 window AC's and 3 TV's at the neighbor's house, but just a light ballast and the power filter board on my HF rig.  If I had had the HF rig disconnected from the power supply it would have just been the light ballast.  Power poles are your friend.

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.

[WRKC935]

27 minutes ago, LeoG said:

So why isn't the tower bonded to the electrical ground through the coax which is attached to the chassy which is grounded through the ground line in the power outlet?  No matter how much you ground anything because of the resistance of wire they'll always be at a different potential?

Yes, there is always going to be a difference.  You bond because coax connectors are NOT high current rated. The circular mills of the shield conductor is also not sufficient to minimize the resistance of the conductor.  This is why you don't use split bolts and crap to do your grounding.  It's all CadWeld or 15 ton compression lugs / connections.  

 

[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.