Question About Lightning Risk For Computers And Phones

Discussion in 'General Electronics Chat' started by Glenn Holland, Sep 12, 2017.

  1. Glenn Holland

    Thread Starter Active Member

    Dec 26, 2014
    We had a nice round of thunderstorms go through the San Francisco area last night with lots of C to C and C to G lightning.

    I live in a building that's mostly wood frame with no formal lightning protection except for an old fashioned antenna on the roof. The antenna has been left intact for those who don't have cable TV and still rely on broadcast. The antenna is connected to a cable/broadcast selector box that is grounded through ComCast's main cable that's finally terminated in a box under the sidewalk in front of the building. So that's the "lightning rod" and the only protection against some other part of the building getting a hit.

    However just to be on the safe side, I disconnect the power and internet connections from my computer and phone when there's a lightning storm in the area. My concern is if lightning hits the antenna (or another part of the building like a sheet metal pipe for a heater vent), it may seek ground through the power and phone wiring and fry my computer and phone which are both essential and expensive items to replace.

    So is this a wise precaution or am I just being paranoid?
    Last edited: Sep 12, 2017
  2. nsaspook

    AAC Fanatic!

    Aug 27, 2009
    Wise precaution. Unless you are very sure about the level of grounding and circuit protection a disconnect is the best thing. Thunderstorms are rare here too but my house is still grounded and protected like I like in the tropics with a bonded loop ground with several rods for the house and antenna connections. I've no external cable or phone connections (dug-up and removed the wire on my property) and the internet is a 100Mb symmetrical fiber-link to my own Linux firewall and router on a well grounded rack-mount.

    Last edited: Sep 12, 2017
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
    We have thunder/lightning storms here on a regular basis, I've never used "surge protectors" and never had an issue. The soil is moist clay and we have a well planted grounding rod at a low spot in the property - I'm sure it never dries to the bottom and even if it did, the clay is never completely dry.

    When I lived in NorthWestern, NJ - I had a two acre plot on the side of a mountain. The mountain was made of rocks about 4 to 10" in diameter and virtually no soil - just rock and sand. The grounding rod could be grabbed and pulled up and pushed back down easily. Over a four year period, we had lightning issues, one with computer, VCR/DVD player and video game console, and, in a second event, garage door opener and a fluorescent lamp in the garage (bulbs broke).

    I think grounding plays a huge role in the process of a lightning strike.
  4. Glenn Holland

    Thread Starter Active Member

    Dec 26, 2014
    I lived in Oklahoma back in the 1960s and one of our distant neighbors antenna got hit and part of the strike went to ground through the house wiring. Obviously, the TV was totaled, but it also started a fire in the walls.

    I vividly recall that incident which occurred after an early morning thunderstorm had "supposedly" past through our area and was headed out of town. I believe the lightning jumped from the "anvil" (that veil of cirrus clouds on top of a cumulonimbus cloud) on the trailing edge of the main part of the storm and its path to the antenna was probably around 30,000 feet.

    My home was about 1/4 mile from the strike and produced a brilliant blue flash through the living room window. Then came the thunder which started with a deep sharp thud followed by almost 20 seconds of rumbling. That was the longest round of thunder I've ever heard and I thought it would never stop.
  5. joeyd999

    AAC Fanatic!

    Jun 6, 2011
    nsaspook likes this.
  6. Glenn Holland

    Thread Starter Active Member

    Dec 26, 2014
  7. Glenn Holland

    Thread Starter Active Member

    Dec 26, 2014
    This diagram illustrates the relative risk of being hit by lightning even if you're next to a tall object:

    Lightning Rod 1.jpg
  8. OBW0549

    Well-Known Member

    Mar 2, 2015
    Wise precaution. I had some electronics zapped once during a storm, so anymore I do the same.
  9. Reloadron

    Distinguished Member

    Jan 15, 2015
    The house beside my sister's home took a direct hit. My sister claimed she actually felt the electricity in the air inside her home. This was before broad band internet and she used a dial up modem. She actually only lost the modem in her home computer. Not bad considering the houses were about 60 feet apart.

    Another friend lived out in the rural areas. House had a grounded lightening rod and was surrounded by tall trees which overshadowed the house. He was in his den with his two boys when lightening struck. The house took a hit on, of all things, the brick and mortar chimney. The house was a wood frame structure. His fireplace literally exploded sending chunks of bricks, mortar and glass flying. One of his boys sustained cuts and bruises from the debris and the majority of his home electronics never worked again. His homeowners covered things.

    My opinion is that small devices like surge protectors are a nice to have all of the nice to have on the planet are not going to do much during a direct lightening hit. We once had a tree explode in our backyard when it took a direct hit. The sheer heat of the strike created super heated steam with every drop of moisture in the tree resulting in millions of toothpicks in a 100" radius. :)

    I see it as a wise precaution. Over all of my years I have seen lightening do some strange things which seem to defy all the rules. Why did my friends chimney take the hit and not the grounded lightening rods on his roof peaks? Why did the strike not hit any of the trees towering well above his house? So does it help to take a few simple precautions? Nope, as you have nothing to lose and everything to gain.

    Forgot to mention when we had a direct hit in close proximity to our home we lost one cordless phone wall wort which was strange. No clue how close the hit was but the only loss was a wall wort. That was peculiar.

  10. Tonyr1084

    Well-Known Member

    Sep 24, 2015
    Here's what I believe I've understood about lightning and how it selects a target: From the illustration below, as cloud energy reaches critical strike levels, the ground begins to send up spires of electrical energy. The cloud above and the ground below seek and reach toward each other. Eventually one of those connections are made and that's where the lightning discharges to, be it the house, the ground, the antenna or the tree.

    Assume you're standing on the ground. Lightning begins to develop overhead. Lets jump to the strike - suppose it hits the antenna and not you on the ground. If you're standing in the location where the spire is reaching up you're being exposed to extremely high voltages. Even though lightning doesn't HIT you, you can definitely feel the charge. So when @Reloadron said his sister believed she could feel the electricity in the house - yes, absolutely. She was likely exposed to one of the much lower level energy spires when the lightning found a critical path to ground.

    Remember in school? Remember rubbing your arm against the plastic back of the chair and how your arm hairs stood out reaching toward the plastic? That's the same thing a person can experience when they're very close to a critical strike. I've felt that once in Big Bear CA, during a mountain thunderstorm. Lightning struck a tree some 30 feet away from where we were digging a trench. Every hair on my body began to stand on end and we all jumped into the trench (3 feet deep). On my way to the bottom I SWEAR I saw lightning exit one side of the trench and enter the other just two feet away from my face. I'm probably wrong about that, the whole thing was over - um - in a flash. But I definitely remember the experience of being really really close to a critical strike. Today I believe what I saw was something I saw out of the corner of my eye and as I was drawn to look it APPEARED to exit the trench wall just two feet away.

    Nevertheless, lightning can hit a lower lying object by chance IF the upward spire makes contact first. So the brick chimney? Yeah, it can hit there and ignore taller trees. Lightning reaches in both directions, and depending on the energy level, the altitude the spire reaches is barely affected by the height of where it begins to reach skyward. So yes, you can feel the presence of a close strike. Many people have been directly hit by one of these spires and lived to tell about it because the spire was not the path the lightning finally took. Standing under a tree or next to a tall telephone pole can increase your chances of being hit by one of these spires. And if lighting chooses THAT path to ground then you can be in serious trouble.

    Unplugging things prior to a lightning storm, while infrequently you may experience a strike, it never hurts to unplug things. Now: Talk about tall thunder? Houston had the biggest storms I've ever known. Most places I've lived, if lightning was more than 30 seconds away (30 ÷ 5 = 6 miles), you seldom heard the thunder. In Houston I've seen lightning that was 60 to 90 seconds away (12 to 18 miles) and the ground shook with the thunder. Read an article where a bicyclist was struck by a storm that was 4 miles away with no clouds overhead.

    In the drawing, let the red line represent the spires reaching upward.