Fixing a computer that was 'struck' by lightning

[westom]

Something that connects the mains ac to the house plumbing through this device would seem like a winner, since you can pass enormous amounts of electricity through water filled 22mm pipe, and the resistance would be low. ...
To the post ages ago about cows near a tree being killed, the bbc reported on it a while ago. They thought the large puddle they were all standing in was the cause, all the cows under the tree were killed not just one.

The same earthing for 230 volt safety must be better for surges. Conductivity, in this case, is not about resistance (lower resistance is a thicker wire). The critical parameter is impedance (lower impedance is a shorter wire). Pipes have solder joints, sharp bends, etc. Factors that contribute to excessive impedance.

The important parameters for better earthing include short ('less than 3 meters'), no sharp bends, no splices, not inside metallic conduit, all ground wires route separate till each meets at the single point ground, and ground wires separate from other non-grounding wires.

Wire impedance is also why a protector is better located close to earth AND farther from the appliance. That 15 meters between the protector and appliance or that up to 50 meter separation used in a BT CO enhance protection.

If the water pipe is solid copper that enters the building adjacent to other utilities, then the water pipe is a good earth ground for surge protection. But only if that ground is also permitted by local human safety codes.

The 'cows' example has existed for generations. A recent event would only be a repeat of what happens often. Another example is sleeping campers. Those sleeping pointed as the struck tree were hurt. Those sleeping tangent to the tree were not a 'better conductor to distant charges'; therefore did no suffer electric shock from a lightning bolt that struck the tree.

Same applied to a house with good earthing at the service entrance. Unknown was a vein of graphite (better conductive earth) on the other side of that house. A surge entered on AC mains, ignored the service entrance ground, and passed through the house to obtain earth on the building's far side. Solution was to encircle the home with a buried ground loop wire. Better earthing meant a surge current did not enter the house to obtain better earth ground.

Damage is how one discovers a flaw to correct it. Unfortunately, few tests to find human 'surge protection' mistakes. The first test is when a surge occurs. If a surge protection system is properly installed, then nobody knows the test has occurred and the system has passed. Best we can do is learn the principles and avoid previous mistakes by others.

First and foremost is to be almost religious about the earthing since every protector is only as effective as its earth ground.

 

[JonJ678]

Indeed, it is the complex part of the impedance which matters for ac more than the real part. Perhaps I can be forgiven for using the more familiar term resistance when I meant the combined opposition to flow of electricity. Solder joints will increase resistance but not impedance, but I agree that bends will increase impedance. Its a sore point that a straight wire has impedance, I can't get that one straight in my head.

Unfortunately your points all revolve around building the house competently, which while we hope will be the case, often may not be. I'm going with fuses as the answer. Ones which blow during a surge but not during normal use, preferably very long ones so that their resistance once blown is huge. I fear practical limitations though.

Basically I can't think of a solution for this. Given a computer plugged into the mains and into a router, how do you protect it? By ensuring it is not the easiest route to ground. How about a small pass through 3 pin plug which goes into the wall, designed to do nothing except to burn out in such a way as to connect the incoming surge to ground? If it short circuits the computer out of the loop, it should save the computer at the potential cost of other appliances. As my computer is worth significantly more than anything else in this room, I think that's a fair trade. Opinion?

 

[westom]

Basically I can't think of a solution for this. Given a computer plugged into the mains and into a router, how do you protect it? By ensuring it is not the easiest route to ground. How about a small pass through 3 pin plug which goes into the wall, designed to do nothing except to burn out in such a way as to connect the incoming surge to ground? If it short circuits the computer out of the loop

Nothing stops or blocks surges. A building is so full of conductive paths that any ‘blocked’ surge will simply find other potentially destructive paths.

A fuse (or tiny pin) will never provide protection for a long list of reasons including 1) a surge will increase voltage as necessary to continue conducting. A fuse has a voltage that, when exceeded, will continue to conduct after opening. 2) Even the fastest 'opening' devices - fuses - take tens of milliseconds to blow. Surges do damage in microseconds. 3) Nothing is going to stop what three miles of the best insulator - sky - could not stop.

The NIST clearly defined what provides protection. Protection works "by diverting the surges to ground. The best surge protection in the world can be useless if grounding is not done properly." After over 100 years of doing this all over the world, that fundamental fact still remains true.

Same principle applies to antenna towers (treated as a separate structure) or even to a buried Norwegian 'nuclear hardened' maritime communication facility (van der Laan and van Deuren in IEEE Transactions on Electromagnetic Compatibility on 4 Nov 1998).

A utility demonstrates how to solve surge damage when utility are erroneously connected:
http://www.cinergy.com/surge/ttip08.htm

Surge protection is about equipotential and conductivity. Attempt to make earth beneath a building equipotential for the same reason that a cow is surrounded by a buried wire loop so that current does not flow up its hind legs and down its fore legs. Ufer grounds are another solution - which is why better protection is installed before the footings are poured.

But we can never achieve sufficient equipotential. So we upgrade conductivity to compensate for insufficient equipotential. A more conductive earth ground includes a lowest impedance connection to even better earthing electrodes. But we can never make conductivity sufficient. So we also need equipotential. Each compensates for the weakness of the other because a protector is only as effective as its earth ground.

To better appreciate how this is done, read principles in Polyphaser's highly regarded application notes:
http://www.polyphaser.com/technical_notes.aspx

 

[Keltik THC]

if your PC is hard wired to your router then it sounds like lightning hit your phone lines, toasting your router and PC.

This happened to me about 10 years ago on a 56k modem, lightning strike, a pop and some smoke from the monitor destroyed that Gateway.

Ever since i always plug my phone lines and plugs through surge protectors, take no chances.

but if surge protectors dont actually work, as the poster above suggests at least with the good ones you get a guarantee covering all your equipment should a surge get passed the unit.

 

[westom]

but if surge protectors dont actually work, as the poster above suggests at least with the good ones you get a guarantee covering all your equipment should a surge get passed the unit.

Good luck getting the guarantee honored. Read the fine print. So chock full of exemption that, as one learned:
> Eventually it boiled down to a line in the warranty that said "Belkin
> at it's sole discretion can reject any claim for any reason".

The protectors that do not claim to provide protection are selling to those who never learn 'free market' principles. A product with the biggest hyped warranty is typically the most inferior. Benchmarks in surge protection have no warranty - instead are selling protection.

If you need a guarantee, buy insurance from a broker who is required to honor your claim.

 

[JonJ678]

Cheers again westom, I'm out of questions.

Much appreciated