Science Questions

Lightning on TV

Sun, 20th Apr 2008

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Question

Clive Wilkins, Sutton Coldfield asked:

My Dad always used to unplug the TV when lightning was nearby, was this the right thing to do? And, if you'll excuse the pun, Watt is the Current advice?

Answer

John Hammond, Met Office:
On average in the UK itself we have about 1 in 3,000,000 people that are struck by lightning so thatís quite a high number.  Most of those do survive but overall the people who have been struck have been doing anything from literally using electrical appliances.  Weíve had accounts of people whoíve been ironing and theyíve been blown across the room because the lightning has come down that particular way.  If you are concerned then I would certainly try and unplug an electrical appliance to try and break that link where the lightning therefore canít go and not make contact with the ground ultimately.

Lightning Hitting the Eiffel TowerDr Bob Howlett, Reader in Electrical and Electronic Engineering, University of Brighton:
Whether you plug your television in or not when thereís lightning around Ė itís an interesting question.  I think itís one of those questions where the answer really is, it doesnít make too much difference.  It certainly doesnít make any difference as to whether you get struck by lightning or not because that is down to the distribution of charge in the clouds and the distribution of charge over the nearby buildings and would you believe, the shape of the building: whether there are sharp points on it and things like that.  One little television aerial isnít going to make any difference that way.  If you do get struck by lightning the current will come down the aerial cable and if your televisionís plugged in it may be a good thing because the television will melt down and absorb the energy.  The bad thing is that the cathode ray tube may explode which is not very nice but the television would act like a nice little fuse and absorb some of the energy.  If itís not plugged in the energyís going to go somewhere else.  There will be a spark from the plug to the nearest earth point which might be a radiator or it might be you or your dog walking past or whatever but you donít know what. 

Even if nothing happens to the television aerial the wet walls will be quite good electrical conductors.  Youíll get quite large current coming down the walls on the outside of the building.  Those changing currents will cause magnetic fields, which in turn will induce EMFs or voltages in what could be any electrical equipment in the house.  Iím afraid the answer is thereís probably not much you can do about it apart from lying back and watching the show.

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My mum always unplugs the aerial from her TV during a thunderstorm. She heard, aparently, of someone who was less cautious and suffered a "telly-detonation" when lightning took a trip down the aerial lead from the roof one day. I've no idea if this is true or not though.

Chris

chris, Tue, 15th Apr 2008

I would say it is better to be safe than sorry!

This also goes for the computer.    Apparently, people forget to unplug the phone line or cable lead in a thunderstorm and a surge could go down the line thus messing up the computer - even though the owner has put in a surge device for the power. Lynda, Tue, 15th Apr 2008

That is definitely true. When I was at school in the early days of computer networks (we had a school-wide Econet network of BBCs!) a bolt of lightning hit a tree near a classroom. The computer was fried and all of the other computers close to it on the network were also internally dismantled, so to speak.

Chris chris, Tue, 15th Apr 2008

I was told when I had my first ever PC and that was in the last decade that each time there was a thunderstorm so that I should unplug the computer or just turn it off, in case I got an electic shock.

I haven't done this yet, but I don't turn the PC off.

But should I do this? It still worrys me a bit. rosalind dna, Wed, 16th Apr 2008

It is better to unplug a TV aerial (if roof mounted) in a thunderstorm as the aerial could receive a substantial charge from a nearby lightning strike. Being plugged in will also lower the impedance to ground and could make the aerial a slightly preferential path for a discharge. Having said this, it is fairly unlikely to be a problem unless your house is prominently on top of a hill as well. How often does your house get struck by lightning anyway? It matters much less if your aerial is in the loft. Telephones are less of an issue, despite the miles of overhead telegraph wires, because there are devices to limit the voltage excursion and any damage from anything but the most severe and closeby strikes. If there is an actual nearby lightning strike, unplugging equipment could save the equipment, but for most people this is a very unlikely event and, unless you consider yourself to be particularly unlucky, probably not something to worry about too much.

graham.d, Wed, 16th Apr 2008

We had a lot lightning damage a few years ago. It came from the phone line. It blew up quite a lot of stuff, two PCs (with internal modems), two SKY boxes and a scart port on one TV. A few other people in the area had modems and phones damaged.

The annoying thing was the SKY boxes still worked but SKY couldn't check that we had the two boxes in the one house as they use the phone line for this.

The insurance company were very good about fixing the stuff. However our premium went up when it should have down since lightning never strikes twice and this wouldn't happen again.

I guess I don't have to worry about unplugging things next time on the same token. turnipsock, Wed, 16th Apr 2008

You can put a surge protector in the phone line (not sure if you can get surge protectors for TV antennae cables, but I could imagine they are available). another_someone, Wed, 16th Apr 2008

In the UK the telephone master socket should have surge protection anyway.

turnipsock, if you have already had a lightning strike I would take the opposite view to your suggestion. It could mean (and this is more likely) that your house is more susceptible than noraml to strikes, and I would be inclined to take more precautions rather than less. But if you can see no physical reason why your house was preferentially struck, then it could be just bad luck. graham.d, Thu, 17th Apr 2008

Apart from the obvious potential for catastrophic damage if you get a direct hit, you might also get a slow discharge down a TV aerial lead if connected to a TV as the charged clouds pass over.

On the other hand, you might not want to be personally touching the lead or plug at all in the middle of a storm. On that basis, if you do decide to unplug the lead, you might choose to do so when the storm is some way off - not when it's right overhead!
techmind, Fri, 18th Apr 2008

We are right next to a church. It had a big hit a good few years ago, it blew the fuse box off the wall. I think it was gods way of saying 'get a lighting conductor'.

Lightning is looking for the easy way to earth and pointy things are an easy way as the field around them extends quite far. Worst place to be is in a swimming pool or on a golf course during a backswing. Best place is in a car (unless its made of fibreglass) or in a house next to a church that doesn't have a lightning conductor. turnipsock, Fri, 18th Apr 2008

I seem to remember the best place to be is a distance away from a tall object of half its height. I don't remember the reasoning but it maybe a minimum field position assuming the ground and the object were all conductors. It is also wise to stand with your feet close together to avoid the voltage difference between them if the ground is not a perfect conductor. If you are right next to a church and your house has had damage from lightning, I would assume this is not a wholly unlucky, random event and would take some precautions. graham.d, Sun, 20th Apr 2008

Yes and you will save yourself a lot of cash . Turn off your computer also Alan McDougall, Wed, 25th Jun 2008

I think it best to turn off & disconnect the aerial or it could act as a conductor. In fact I think it often best to turn off the TV even if there is no storm. Saves you being subjected to a whole load of %$*"x@ such as Constipation Street. Don_1, Thu, 28th Aug 2008

Yep we have lost computers here in lots of times whole offices have their computer systems wiped out in thunderstorms and it is always best to unplug the TV etc.. during thunder and lightening storms.. I unplug my TV, RADIOS, AND REFRIGERATOR.. I have been known to stay on line until my power surges to much then I unplug and move to my phone! LOL..Computers are too expensive for me to be replacing! Karen W., Fri, 29th Aug 2008

Karen now that I've got cable broadband/TV that I'd better turn off the computer and the radio/TV but mainly it's just rainstorms. rosalind dna, Fri, 29th Aug 2008

I just do it during thunder and lighting as my homeowners does not cover damage from acts of god or Mother nature! So I unplug, surge protector or no... I would hate for the computer to blow in front of me whilst working on it! Karen W., Sat, 30th Aug 2008

I worked as a TV service tech for 30 years and found many instances of minor damage due to lightning but never any thing major,
Houses that received their power over overhead power lines often had the receiver fuses blown but little other damage, small holes were burnt in the antenna cable as it passed over metal guttering but did not destroy the antenna.
Switching off the receiver is irrelevant as any surge will easily spark across the switch contacts, unplugging the antenna cable and power cable (and placing it next to the power socket will best protect the receiver) but after a while this leads to the antenna socket getting broken! syhprum, Thu, 25th Sep 2008

25 000 ++++++ posts  Karen I am really impressed, I have belonged to  a number of forums and no one has come anywhere close to that number of inputs 

Take care

Alan
Alan McDougall, Thu, 25th Sep 2008

Not very impressive.. I just like the forum! Karen W., Sat, 27th Sep 2008

observe lighting is one of the most wonderfull things in the world. erickejah, Mon, 20th Oct 2008

well, i too have experienced this situation and my old tv. set was damaged due to it. many mechanics tried to mend it but it didnt work as well as it used to. so i guess it is better we take care of it.
coz precaution is better than cure..!! Sanghamitra Dey, Wed, 22nd Oct 2008

My view i that lightning striking the earth has managed to travel several thousand feet from the clouds, pulling the plug out will add a couple of feet to the route at most.... I won't tempt fate by typing what I then thought! BH, Tue, 28th Oct 2008

It REally Depends On How bad the thunderstorm is.
If it is really bad then every thing off,
If it is not bad then you are ok to keep the electric on!
:D DanilovesHim, Tue, 11th Nov 2008

After two times with "fried everything", I definitely vote yes.
Unplug everything, including the phone/DSL line (!)

Phone thing (the main controlling box in the cellar) "jumped" off the wall, leaving a nice charry black mess behind.
TV/phone/computer(DLS line -> mainboard)/printer were all toast.

Severity of the thunderstorm didn't seem to matter much.
First hit was during a somewhat bad but very close thunderstorm.
Second hit was during a very mild one (with one sudden extremely loud bang)

(I do not live in a very rural area, plenty of trees and other houses around.) highwaykind, Fri, 28th Nov 2008

turnipsock "However our premium went up when it should have down since lightning never strikes twice and this wouldn't happen again."

Yes Sir, and as true as it is stated.
Just once more prove the absolute incompetence of the insurance companies.

The nincompoops, wanting me to pay for the damages.
She run into my car I say, head first!!!
yor_on, Sun, 30th Nov 2008

I think a lot depends on whether your mains power comes via overhead lines as is common in America or by underground cable, if the later you have little to fear from power line surges so carry on viewing but overhead power lines can be a menace.
lighting surges down the aerial cable are another matter if the lightning is real close unplug the cable and place it near something earthed and carry on viewing with a set top antenna if possible.  syhprum, Sun, 1st Feb 2009

Europe here by the way, cables underground.... highwaykind, Sun, 1st Feb 2009

so if in America turn your TV off because the cables are above ground, but if in Europe you (most of the time) wont have to because of the cables being underground.
I usually turn my TV off if there is lightning just to be on the safe side because a bolt could hit the areal... does it matter if your TV is on or off when a bolt hits your areal, i don't see how it does but my dad always says to turn it off anyway. tangoblue, Sun, 3rd May 2009

Yes. Jdubs, Wed, 6th May 2009

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