lightning rods

[tomplum]

I used a friend's rotohammer & it worked well on all dozen 8' rods I instslled even in out hard clay. You wantvas much contact between the dirt & rod as possible. Driving the rod in like a nail gives optimal contact. Digging a hole or using a water jet especially creates a hole bigger than the rod. It will sit loose in the hole & give you a much worse connection to ground. The higher the resistance to ground, the higher the likelihood that the lightning will find an alternate path to ground. Murphys law says that other path will be something that will melt, catch fire, or otherwise Bevan expensive repair.

The rod doesn't stay loose in the hole for very long. It is a wet job, but gets done quick and in the end the result is the same. Another plus is not having to extract the rod when you get it half way in and hit a rock that says you shall not pass.

 

[deereman75]

When I built my yard we trenched between all the buildings and the pole. Instead of rods at each building, there was a heavy copper ground wire buried in the trench alongside the service cable. They all tie together back at the pole and into the grounding grid of the pole. It's a hell of a lot more contact than you'd get with any reasonable number of rods....

 

[Fallon]

The rod doesn't stay loose in the hole for very long. It is a wet job, but gets done quick and in the end the result is the same. Another plus is not having to extract the rod when you get it half way in and hit a rock that says you shall not pass.

Just like any other compaction job, it takes years for dirt to settle. If you aren't compacting in 6" lifts it's not compacted. Try getting a fence post to stay tight in a hole if you don't massive tamp in the backfill every few inches. A ground rod is even worse as you aren't getting any backfill or compaction a fraction of the way down that hole.

You need maximum surface area contact between that dirt & rod. If you put the rod in a hole even a little bit bigger than the rod it will only make intermittent contact with dirt. You'll end up with a high resistance ground.

I had a friend who was a sparky in the air force. In some bases in the desert they would excavate around the buildings & weld 4x8 sheets of copper plate together all the wayvariund the building then backfill & compact properly. The dry sand ground was so poor of a conductor they needed to go that far to get good low resistance conductivity to ground.

There are specialty multimeter type devices you can use use to verify how well your ground system is actually working. They usually show bored holes not working well unless the ground is super conductive & moist year round.

 

[Grumpycat]

Actually, electricity mostly flows along the surface of the wires, which is why the conductors for lighting systems are multi-strand braided wires instead of one big wire. More surface area means more conductive capacity, which is why those wires don't melt. (This is even more pronounced at higher frequencies.)

Wrong. If anything stranded wire has a greater resistance than same AWG in solid. Look up AWG wire current capacity tables. This site says stranded has lower current carrying capacity but most codes do not distinguish between stranded and solid: Stranded Wire vs Solid Wire in Electrical Applications

Current flows in fields at and near the surface of conductors. Bundled conductors aggregate the effective diameter not the areas. High power utility lines have steel core for strength surrounded by aluminum for conductivity. Note really high voltage systems bundle 3 conductors several feet apart as one conductor to increase the diameter of the electric field. Those 3 spaced apart have less total losses than 3 individual conductors.

 

[Grumpycat]

When I built my yard we trenched between all the buildings and the pole. Instead of rods at each building, there was a heavy copper ground wire buried in the trench alongside the service cable. They all tie together back at the pole and into the grounding grid of the pole. It's a hell of a lot more contact than you'd get with any reasonable number of rods....

Is not just a matter of contact or depth in the ground. In some situations the best "ground" is to be had laying a long bare wire on top of the dirt. That works everywhere but can be a nuisance.

 

[fishdrivel]

Are they even installed much anymore. I see large all metal building and roofs without them. Any need or are they really that effective?

I oversaw construction of military facilites and they were definitely needed and effective. Most lightning rod installations I have seen off-base are questionable. There is a lot to getting them right. Grounding requirements for ammunition storage are complex!

 

[deereman75]

Is not just a matter of contact or depth in the ground. In some situations the best "ground" is to be had laying a long bare wire on top of the dirt. That works everywhere but can be a nuisance.

The burying the bare wire in the trench eliminates that nuisance

 

[ning]

When I built my yard we trenched between all the buildings and the pole. Instead of rods at each building, there was a heavy copper ground wire buried in the trench alongside the service cable. They all tie together back at the pole and into the grounding grid of the pole. It's a hell of a lot more contact than you'd get with any reasonable number of rods....

I'm under the impression that very dry ground is a poor conductor and therefore a poor electrical ground (thus why electric fences don't work well when the ground gets really dry unless you're expecting the fence to zap between the hot wire and part of the fence instead of the ground).

My ground here is bone dry two feet down in the summer, but when you pound a rod down deeper you start getting a decent year-round ground.

I guess the ground ring or ground-in-a-trench works because there's just so much more ground contact that it makes up for the higher resistivity of the potentially drier soil?

Interesting related article: https://www.ecmweb.com/content/article/20892049/achieving-an-acceptable-ground-in-poor-soil

 

[CobyRupert]

Wrong. If anything stranded wire has a greater resistance than same AWG in solid. Look up AWG wire current capacity tables. This site says stranded has lower current carrying capacity but most codes do not distinguish between stranded and solid: Stranded Wire vs Solid Wire in Electrical Applications

Current flows in fields at and near the surface of conductors. Bundled conductors aggregate the effective diameter not the areas. High power utility lines have steel core for strength surrounded by aluminum for conductivity. Note really high voltage systems bundle 3 conductors several feet apart as one conductor to increase the diameter of the electric field. Those 3 spaced apart have less total losses than 3 individual conductors.

What you’re talking about is “skin effect”. It’s only a thing with AC currents. With DC currents, the current will be uniformly distributed across the cross section of the conductor. With 60 hz AC currents, skin depth is about 8.5mm.
One has to be careful with conductor ampacity charts if you’re using one for the other, or if you have 400hz as is common on air planes.

 

[Grumpycat]

One does not install lighting rods to conduct direct strikes to the ground. Lightning rods work by dissipating static electricity. Stranded wires are only used for the convenience of the installers. Solid wires are more reliable.