Are lightning strikes dangerous to appliances if supply lines are buried in ground???

I recently added a 3rd computer and now have about $15K worth of electronics plugged in so I was needing another surge protector. So I went shopping and holy moly those things have gotten expensive. Last time I bought one it was about $30. Now for the same thing they are running about $130. Then I got to thinking that since my home electric,cable, and phone service are all underground service for atleast 250 ft., shouldnt I be protected good enough without surge protectors?
I would think that lightning striking a power line somewhere and entering the ground would not return out of the ground to my home. Wouldnt the power pole outside my home route said electrical surge into the ground before entering my home even if it did come that far?

I have talked to several people and gotten mixed answers to this question. My personal opinion is that the electrical surge would ground itself out wherever the service line enters the ground and it would not enter my home.

What do you think?

I never knew they made a surge protector for the service box..hmmm..guess I might be giving a call to an electrician and checking hardware stores. I'm an ASE certified auto tech so I am pretty good with electric and electronics, and I dont think I would have any problems installing a surge protection device on the main service line. My service line comes out of the ground on a 3 ft. pole and goes into a dual 100amp breaker box, then into my house breaker box, so I would assume that the surge device would have to go before both breaker boxes. Correct? I work on 600volt hybrid vehicles at work so I have the necessary safety equipment available.

I have homeowners insurance but it only covers about $10K contents...yes, I know I'm underinsured, but the rates go through the roof if I get anymore protection. Not to mention the fact that if I filed a claim, they would jack my rates up and I'd pay for the repair or replacement in the long run anyway.

Frank:

You are at risk. The reason why is called "ground rise potential", sometimes called surge voltage. When the lightning strikes nearby there can be a substantial potential (voltage) difference between wire conductors even if they are normally at ground. The potential difference can be direct or induced (coupled) and it can be sufficient to damage your equipment . For instance a nearby lightning strike can induce a surge voltage into your house wiring that wants to find its way to ground any way it can. The copper water pipe burried in your yard could momentarily be a better ground than the power system ground so there could be a substantial surge potential difference between them and that copper water pipe near your computer could be the path to ground the surge voltage decides to take. You get the idea. Protectors which have MOVs that operate quickly can "short" this potential difference before it rises to a dangerous level for your equipment. An investment in protectors is worth the investment.

The March and April issues of QST have a very good discussion about the issue. Go to www.ARRL.org and order copies of both issues. It is a bit technical, but I think you will benefit from reading it and be able to make decisions pertinent to your situation.

9 June

Frank: Your point of presence is on the house side of the meter. Do not add protectors on the line side of the meter. Hire an electrician who knows the code in your town. If the installation is not per code you will have an issue when you sell the house or if the code inspector has some reason to inspect (not a high probability, but not zero). You may need a building permit. Check.

I will offer you my opinion. I am a graduate electrical engineer but I would not even think of adding protectors at the mains of my house myself. That is a job for an experienced electrician. I have the design experience but not the "doing it" experience. Like you, I have worked on big transmitter power supplies like 10 KV for a high power klystron and I'm comfortable working on the 120V and 220V distribution in my house, but working on the AC mains, man that's another story. Too risky to me and my house. Wouldn't do it!

Good luck and be safe - 73 from the Fisherman

Just like electricity comes yo your home, so can the power surge no matter HOW far down the cable (or whatever) line is! If you need a cheap protector www.ewaey.com and www.ebid.NET are great places. (EBAY SUCKS)

If the supply lines (and phone lines and cable TV and everything else) are underground, then the risk is greatly reduced. However, they have to come aboveground someplace to get into your house so you can use them, so there may be some vulnerability there. The wires sometimes have little above-ground cabinets every half-mile or so where service personnel can get to the lines (instead of having a manhole). Plus, bear in mind that the conduit in your house is (usually) metal and may not be properly grounded. If lightning strikes your house, all it needs is one little pathway to your wiring, and it could then blow everything on that circuit out. Say you have a TV antenna outside - if it takes a strike, the power could go through the TV, through its ground connection, and take out every sensitive device in the room.

Well, there's the problem. You're partly right that once a lightning strike has hit the ground, that's it. It's not coming back up out of the ground. (Hint; that's why the safety return path for electronics is called 'ground'.) But it's not the actual lightning strike itself that is likely to damage your equipment.

If lightning actually struck your equipment, the entire wall would be vaporized, or a raging fire at least. A lightning strike close enough to your house could induce a spike in the voltage in your wiring. Think of a transformer in which electricity goes into a primary winding. There is no direct connection to the secondary, yet current flowing in the primary induces current flow in the secondary So it's not the lightning strike itself, but the proximity of the strike as it's going to ground that can cause the damage.

The cheap surge inhibitors (can't legitimately call them protectors) like those found in $10 power strips aren't worth a nickel. A lightning strike will jump through that so easy it won't have time to protect anything. Good ones are expensive.

Me, I don't bother with them. The chance of a lightning strike damaging my equipment is nearly non-existent. In over 40 years, it's never happened. That's not to say that it can't or won't. but that's the reason I carry homeowner's insurance, for the unlikely event that it does occur.

With all that equipment, especially if you live in an active lightning area, I'd recommend you get whole house protection installed. This is done at the breaker box where the electric service comes into your home. It can protect everything in your house much better than cheap surge strips. You'd need an electrician to install it correctly but if you consider your investment, it's really cheap insurance in the long run.
But what the one other answer says is true. Spikes and surges coming in the electric line are fairly rare. Still, it can and does happen on occasion.