lightning rods

[RalphVa]

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

The first thing we did when we bought this house in 2000 was to have a lightning protection system put in for the house and then extended it to the carriage house when we built it.

There were 2 house along our road that had been hit by lightning when we looked at buying.

Very good protection if your house is on a knoll.

 

[sunandsand]

Bonding between the ground rods: According to vendor, not needed in this situation. Sufficient counterpoise with proposed system (rod at each corner of 50 by 90 steel building). Now I need to go look that up, but it appears the big roll of #4 copper wire is staying on the shelf for now.

Best regards,

Mike/Florida

 

[Fallon]

Pretty off-topic but if you REALLY have a problem driving the rods in, just cut it off a foot below the top and only drive in one foot.
It's not like the inspector knows how much is below ground.

Obviously, don't do that, cuz your ground will be crap. But still this is what I noticed after spending an hour driving an 8' rod into our hard pack next to my solar array last fall. Inspector saw the top of the rod at ground level with the ground wire & clamp and was like "yup"

Alternatives to driving a whole 8' rod in is multiple shorter rods. I didn't pay attention to the code for that because I was able to get what I needed done (the right way - I may think up wrong ways that are enough to hoodwink an inspector but I don't follow through).

A better legal & safe way to to it is dig a trench as deep as feasible & put the foundation rod in sideways. You still get the dirt contact you need to get a good earth ground. Not as good as vertical but full length but better than a short rod.

 

[jmccaughan1939]

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

Check with your local fire department and see if you are in a high strike area, and yes they do exist. If you are not in a high strike area the normal code grounding should be sufficient.

 

[Fallon]

I put up a 60' HAM radio tower & did a fair bit of research as to code & best practices a few years ago. I have a dozen ground rods connected in a radial pattern. All thermite welded to each other or welded to the rebar in the foundation & guy anchors. Tower tied into the ground with 3" strap. The whole shebang bonded to the house electrical ground. Maybe overkill, but lots of lightning here in Colorado & it's a tallish metal tower.

The key to any lightning system is get as low of a resistance path & direct to ground as possible. Connecting the tower or whatever to the house ground seems counterintuitive, but it's better to get things to ground. The alternative is arcing between unconnected things.

Modern code generally specifies 2 ground rods around 8' apart bonded together. Older code only specifies 1. The more ground rods the better. Ufer grounds are good too. Basically connecting the ground to rebar in foundations or concrete. Concrete is more conductive than dirt & won't blow up if hit.

All ground connections should be properly bonded together regardless of an electrical ground or lightning ground. You are also suppose to bond any metal structures within I think it was 5'. Metal roof, fence, HAM radio tower, etc. Things being bonded prevents arcing between things. If lightning can jump across miles of sky it can easily arc across a few feet if that's the shortest path to ground.

Heat & electromagnetic forces are huge problems with getting lightning to ground. The massive amperage in a lightning strike turns any conductor a massive electromagnet. It will cause ground wire to tear itself off a ham radio tower with hundred lbs of force. So you need to secure it well. Coax cable will literally explode due to the forces. Sharp corners cause inductance issues increasing resistance to get lightning to ground. That's why ground straps end up looking not tightly & neatly routed as you may expect.

As others noted due to various reasons, lightning flows on the outside of wires. So copper strapping actually can take a lot more power than round wire. It also cools off faster. Braided copper strapping isn't actually good, especially outside. Corrosion between strands causes higher resistance & problems.


You never want to solder grounds or high voltage wire. The heat from a lightning strike can easily heat up things enough to melt the solder.

 

[Frankenkubota]

i've always heard ben franklin invented the lightening rod and did not patent it. sort of like his gift to humanity?

 

[Fxfymn413]

The standard that specifies how to do a lightning protection system cited by the building codes is NFPA 780

NFPA 780 Standard Development

Stay informed and participate in the standards development process for NFPA 780

www.nfpa.org

Lightning protection and electrical system grounding are totally different animals.

The best way to drive a ground rod is with a roto-hammer.

One of the ways you can provide some protection from lightning and other surges is to install a "whole house" surge protector in your main panel.

The most over-looked and under used protection is to install some kind of detection device in the attic space that is tied to your smoke detector system. They make rate-of-rise and heat detectors which are suitable for attic installation that will at least tell you that you have a problem in the attic. If you have an out building they are also suitable for that.

 

[CobyRupert]

Yes, NFPA 780 is the standard on how to INSTALL a lightning protection system….but where and what code says you need one?
I’ve never found one.

I believe NFPA 780 itself has a “quiz” that can be used to evaluate whether a lightning protection system is needed on a building or structure. It gives a score based on where in U.S. your located, height and area of building, surrounding objects, whether combustibles are stored, other contents and uses, etc..
The way the questions are structured, the results pretty much ALWAYS say you need one on every building… and the dog house too.

Something that’s often overlooked: Don’t put your down conductors in a ferrous metal conduit, unless you bond the conduit to the conductor itself.

BTW: One of the the purposes of Grounding is to drain static charges. The other is to induce a large amount of fault current during a short circuit, rather than a small amount.
Lighting rods are used because they are pointed, the pointed tip is where electric field lines are most dense (See Gauss’s Law on electrical flux) where lighting will most likely conduct. That, and it’s a low impedance path directly to ground.

 

[Grumpycat]

here's a trick i learned the hard way. if you are having trouble pounding the rods into the ground, run a little water down the rod, just spill a little on the rod and it becomes much easier to drive.

Use a hammer drill to install.

 

[Fallon]

Use a hammer drill to install.

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.