Home electrical grounding question

[CumminsPower98]

Last November I setup a personal weather station and mounted my anemometer to a steel pipe mast that is 33 feet high. This mast is mounted to a metal semi trailer. I have 240v/100A power running from a mobile home load center to a sub panel in my shed. From there the power runs to a second sub panel in the semi trailer. Yesterday I bought and installed grounding lug bars for these sub panels so I could separate the grounds and neutrals as the panels didn't come this way. I removed the bonding screw that was in the first sub panel.



This evening I sunk an 8' grounding rod and ran #6 copper from that into the last sub panel. I bonded the #6 copper to the semi trailer on the way up to the panel to give the anemometer mast a good ground. I ran the in-line anemometer surge protector #12 AWG ground wire into the panel ground bar. I may sink a second ground rod at some point as well.



My concern is having this lightning rod, um I mean mast tied into the home system. If there was a direct hit could this cause damage or would it go to earth ground first assuming I have enough rods in the ground. Someone on another forum who sounded like they knew what they were talking about said I should have it all tied together. So the question is should I leave it all tied together or put the mast/trailer on a separate rod from the home system? I just want to see if I can get a few more opinions.

 

[EricBu12]

voltage likes the least resistance so to ground it goes.

 

[Skydiver]

It is true that you have built a lightning rod. You can never have too many ground rods. A hamm radio forum would be my thoughts for best info.
My friend who has a 50 free standing tower has 4 ground rods within 2 feet of the base with heavy braided wire.
Lightning will take the path of least resistance as we know. Try to make the transition from the pole to the rod as straight as possible. Lightning does not like to make sharp turns. It might start out on a ground (or other) wire then exit to another path.
A direct hit from a lightning bolt will take out most anything. The fingers as I call them of static discharge can be dealt with. It's been many years since I've researched lightning arrestors. Years ago a MOV (metal oxide varistor) was the best for trapping static discharge. The main thing is if your mast or lightning rod takes a direct hit you want most of that energy to go to ground and not cause a fire.
My home took a direct hit in 2001. I had a new computer with the best lightning protection money could buy. It all got fried. T R I P P - L I T E surge protector company tried their best to get out of paying to replace my computer. I did what they said and paid (another company or 3rd party) to for a letter saying that my computer was fried. Had to hire a lawyer and still did not get all my money.
One thing I do when a lightning storm appraoches is get all my induction motors running. Central air, deep freeze, refridgerator. An induction motor can soak up a small amount of lightning thus protecting other appliances. Your electronics operate (ICs and such) on 1-5 volts and can't take much surge.
2 years ago I saw a tree get hit by a very strong lightning bolt 110 yards from my front porch. That event changed how I think about lightning. Massive amount of energy. Later we walked across the road to find tree bark all over the ground. That large tree was dead within 4 months.
Remember that the phone line can zap things as well.
May I suggest, Wind Map - South West United States Observations
Yes, you want as many ground rods as you can afford properly connected.

 

[fest3er]

Lightning will take the shortest path to where it's going. But there's a big 'but' here. While it is heading to ground, the voltage on the stuff around it rises, and that voltage propagates along the wire at a known speed. If your house is sufficiently far away, it probably won't see much of a voltage surge. If it's closer, it could see a 100-300VAC surge for a few micro-seconds. If it's really close, it could see kilovolts for more micro-seconds. It's like dropping a big rock into a pond, where a wave flows out from the rock. With lightning, a wave of high voltage flow out form the point of the strike. Once the bolt is done, the point of the strike starts returning to normal earth potential and a wave of 'zero' voltage flows outward, which pulls the wire voltage down. Voltage and duration vary from strike to strike. That variance changes how far the surge travels along affected wires and how high the voltage will get.

Your best bet would be (1) to install a lightning rod atop the mast, something with a sharp point. The point serves to dissipate the rising voltage before it can build up to damaging levels, and (2) install a whole-house filter in the panel in the house's panel, attached to the breaker for the shed's subpanel. Tytewad makes a nice unit that really does work. Give the lightning rod its own ground rod, separate from the electrical circuit's earth rod; you want to try to encourage lightning to stay away from the electrics.

As to electrical circuit grounds (earths), everything should be tied to a single point so that all equipment is at the same potential above earth. I don't think I've ever seen safety grounds (green/base) and neutrals (white) separated past the panel; they're all attached to the same bonding strips. And, if you think about it, you want the neutrals and grounds to be at the same potential; they're really the same thing, just redundant paths.

IIRC, Dad has to weld a #6 to each leg of his ham tower, attach each of those to its own ground rod and have a continuous loop around all three rods18-24" from the concrete base. He also ran a #6 back to the house in the the trench and connected it to the older rod he sank for his dipole antenna. The electric we ran out there is just tied to the house in its own conduit. The antenna wires are grounded by the tower and by the house. We even included provisions to ground the center leads of co-ax for cables not in use.

 

[CKelley1]

fester3 is not correct on the bonding, neutral theory. leave your grounding just as you have it. at the mast drive four 10 foot ground rods in a square pattern about 4 feet away from the mast, run #6 wire connecting each and run a #6 wire on the mast to the ground rod closest to the mast. try not to put any sharp bends in the wire. lightning does not like to turn corners so make it a smothe arc to ground. pm me your phone # if you need explanation of either one

 

[DennyDay]

fester3 is not correct on the bonding, neutral theory. leave your grounding just as you have it. at the mast drive four 10 foot ground rods in a square pattern about 4 feet away from the mast, run #6 wire connecting each and run a #6 wire on the mast to the ground rod closest to the mast. try not to put any sharp bends in the wire. lightning does not like to turn corners so make it a smothe arc to ground. pm me your phone # if you need explanation of either one

With out using a Megga Earth Ground meter, how do you know if you have a good ground? I've installed ground grids for transfering flammable liquids, and it was proven to me, that with out a meter, you have no idea what you have. Even pouring water and salt around the rods you just can't be sure.

 

[Skydiver]

Good point C. D. Day. Would a volt meter using an extention cord, checking from the hot (120 volts) side to the new ground tell much?
During a drought I sometimes run a little water on my homes ground rod. We have a real sandy soil.

 

[CumminsPower98]

My dad stopped and talked to a local electrician today. He said I have the sub panels setup correctly with the grounds separated. He also said I should have a rod at each sub panel or tie both panels to one rod with #6 copper. I will just drive another rod at the first sub box. He said since it's so dry and sandy here they have started using two rods for a house as well as connecting to the rebar in the concrete foundation. I guess he also talked about using plates and salt in some places but I wasn't there so don't really remember the details. Anyway I will go ahead and do a separate system for the mast.



Wetting the ground rods sounds like an interesting idea. I just need a dripper system to keep them wet. LOL. This electrician mentioned a meeting he was in where they talked about drilling a big hole and filling it with clay for some installations. Thanks for the replies all.

 

[DennyDay]

Good point C. D. Day. Would a volt meter using an extention cord, checking from the hot (120 volts) side to the new ground tell much?

During a drought I sometimes run a little water on my homes ground rod. We have a real sandy soil.

No - - This will not check for earth ground, but will check system ground. Dry, sandy soil is a big problem and calls for extreme measures such as additional ground rods, covering a wider area and put deeper in the ground. Unfortunately using water to improve the system is not a good alternative. If the ground held moisture you wouldn't have a problem. The only way to check earth ground is to measure resistance (in OHMS) between ground rods. To get a good ground, 10 OHMs or less, I've had to use as many as ten (10) rods. A littler over kill for a home system. The ten OHM is a Canadian Standard for flammable liquids, the US does not have any standard at this time, so you have to depend on your electrical contractor. Good move Cummins98, getting a specialist involved, he won't steer you wrong and knows local soil conditions

 

[Dieselnut59]

I had a huge lightening strike about a year ago that was a direct hit on a tree out by my shop. My 2003 Dodge was parked under the tree. The charge blew a trench in the dirt under my truck and between the dual wheels. That hit blew out the computer on my truck. It also burned up one of the transformers on the pole and fried the electrical meter. Only thing it got inside the shop was a Dewalt battery charger.

At the house, it toasted my computer, surge protector, satellite receiver, feed horn at the satellite dish, cordless phone and answering machine. It burned up the phone line under the house and blew the fuses at the phone box. I was extremely lucky it did not start a fire at either the shop or the house. I have three ground rods at the shop (400 amp 3 phase service) and one at the house (150 amp service).

A good idea to keep the ground rod area moist would be to pipe your air conditioner's condensation drain line over to the ground rod's location if possible.

 

[CumminsPower98]

Wow, that's a lot of damaged stuff but glad you didn't end up with a fire. I had a car parked near a tree that was hit one time and had an old CB radio in there and it fried that. That's the only time I have had anything lost to lightning.



It's interesting how the static charge in the air can affect stuff. On the last three T-storms I have noticed that my temp and humidity will dash out for a few moments on my weather station console when there is lightning in the area (doesn't have to be real close either). All the other sensors stay online so today I called tech support and they are sending me a replacement sensor board and hopefully that fixes it.