lightning strikes

Hello,

We've had two thunderstorms inn the last three days. I realise I am not sure what are sensible precautions to take and what are old wives' tales: unplug the tv and don't use the phone seem plausible but keep away from radiators, windows, and don't have a bath? Are they good ideas or just mad?

Our tv equipment is plugged into one of those Belkin surge protector extension leads, as is the computer but they look untidy on the floor. I was thinking about getting more sockets put on the ring main to tidy up these cables. Are there any cheap surge protector sockets, or are the extention leads the cheapest way? I see that CPC sell some sockets but IIRC they are £14 each for the surge protection and even more for ones that filter RFI. By the way, is the RFI filtering worth having? Do you know of any cheaper ones? I would have thought there would be a demand for these protecting equipment in offices and industry?

What about telephone and tv protection? Other than the extension leads, are protected sockets available?

I was thinking about the aerial cable. If lightning strikes, the current will have to travel down the cable to the suppressor in the extension lead. Won't it have melted the coax by the time it gets downstairs? Shouldn't the suppressor be as soon as the cable enters the loft?

To complicate things even further, we live in a dip, so we have to have the aerial on a 16' pole and even then we need a masthead pre-amp. That amp requires a power supply, so would I be right to think the suppressor has to be after the power supply? Would it block the power otherwise?

Is there anything I can do to prevent the 16' pole attracting lightning? Whilst I realise the odds of a lightning strike are 1 in

3,500,000, there was report on the news about an unexposed house in Derby being destroyed after lighting hit their aerial.

I guess these precautions only protect against small charges from distant lightning? I guess a direct hit would be so powerful it would melt whatever earthing or suppressors you had connected?

One last question: is there some sort of surge protector you can fit at the CU to protect the whole house?

Thanks, Stephen.

Reply to
Stephen
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Nothing is going to stop the effects of a realy close or direct strike. Many so called surge protectors don't actully provide much real protection anyway because a lot of damage can, and is, caused by the currents induced in internal wiring or even directly in the equipment.

Peter Crosland

Reply to
Peter Crosland

The idea that a surge protector csn protect againt a lightning strike is one of those misunderstandings the manufactureres only encourage. What they really do is introduce a fire risk and take your money.

TVs, PCs etc already have filtering built in that are orders of magnitude more effective than a surge supporessor, but even those are completely unprotected against a strike.

NT

Reply to
NT

There are two different events to protect against. A direct hit, which is very rare. High voltage pulses delivered via your services, due to a nearby hit, which is more common. (Local situation can adjust the relative importance of these.)

There are two different things to protect. Injury and death. Your property (both home and electronic devices).

These two orthognal sets create 4 cases, and handling each of these should be done as a separate risk assessment.

However, in most cases, the output of a risk assessment in a domestic situation is likely to be "change nothing". I might only add on top of that, avoid using a landline phone or handling the TV and aerial whilst there's a lightning storm overhead.

See if your insurance covers damage due to lightning. In domestic situations, that's about the only protection of property which is generally of any use. Nothing much

If you do the maths, it's cheaper for the manufacturer to actually put nothing in domestic surge protectors and then just pay out for equipment which gets damaged.

If you want effective surge protection, that's something which has to be designed into an installation when the wiring is laid out and when the services are initially connected up to the house. It's not something you can do effectively by buying a few surge protectors and adding plugging them in to an existing domestic system.

If you're talking commercial installation and paying commercial prices for protection, then full protection against even direct hits is standardly provided. It would cost you many times the replacement cost of all your domestic equipment and wiring though, which is why it's not viable in a domestic setting.

Yes. It's done by having the phone cable enter the house as near as possible to the main earthing terminal, and routed (in steel conduit if it's any distance or unavoidably near any other wiring) to that terminal where a surge protector is fitted (usually with gas flashovers) and a short fat connection to the main earth terminal.

In a commercial setting where protection was required, the aerial pole would be earthed as part of a the lightning conductor system.

The aerial wire in an incoming service, and handled like the phone connection above, if you really want to do this properly.

No, but you can make sure a strike on it is harmless, if you want to throw lots of money at the problem.

This goes back to what I said at the beginning. You have to decide which type of event you are trying to protect against. You can do both, but unless you have several million quid of electronics, such as a local area phone exchange in your home, it's unlikely to be worthwhile.

BTW, BT equipment takes about 600 lightning strikes a day, across the UK.

Depends on how all your services are routed.

Reply to
Andrew Gabriel

I've had several bits of electronics damaged by a nearby strike (probably via power and/or phone lines, as these are both overhead cables in my area) - lost cordless phone basestation, laptop modem (rest of laptop ok), and a lamp dimmer.

Realistically, the best protection for your home is insurance.

The other stuff is just mad old wives tales.

Apart from the one about not having a bath.

Unless you hold a silver fork between your teeth.

You can run calcs to check if your property is at significant risk here:

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limited free trial - used to be a free download though, easy to use when I ran the numbers on my place)

Reply to
RubberBiker

I don't believe these surge protectors do much except for con people out of a few extra quid for a 4-gang extention lead. I bet if you took one apart there would be little more than a couple of capacitors and an inductor or two to act as dampers, which would cost pence.

They're a bit like the revolutionary "soft eject" of tape decks twenty years or so ago which consisted of a gob of rocol snotty grease on the mechanism to load it and has been used on tuning inductors since the 60's :) Everyone thought they were really innovative!

The switched mode PSU found in PC's will smooth out any voltage surges anyway, so the surge protecting sockets are moot! I've never heard of anyone's PC from crashing because of a voltage spike.

Reply to
Davey

Depends how crap the power supply is and how the intensity of the last and final noise it made before its caps spewed the guts. A spike will trigger that, and the customer will make the journey back to PC World for the surge protector for their next attempt at IT.

Reply to
Adrian C

Davey wibbled:

Agree. Back in 1986, when I was at York Uni, they used to have terrible problems with induction from nearby lightening on the bundles of overhead RS232 cabling in the walkway roofs.

The RS surge protectors were useless.

So I got a summer job designing some new ones. IIRC the RS product certainly contained a gas tube and a varistor of some sort but not much else.

I set up a test rig using a van de Graff in the physics dept and a test board with sacrifical 232 driver chips (cheaper than blowing up a Wyse terminal).

The RS ones blew the line driver chip after one strike.

By the time I'd finished I had a fairly cheap circuit based on the same gas tube and similar varistor, but augmented with resistors, capacitors and a high power zener, the zener being the component that made the difference.

After some tweaking I could present more than a dozen direct strikes from the van de Graaf before the chips showed any signs of suffering, so it was deem a success. I dare say, it took the RS232 out of spec, but it could still run at 19200 which was good enough for the job. Guess what next summer's job was :)

Reply to
Tim S

A "soft eject" tape mechanism?

Lightning rod holder?

:D

Reply to
Davey

Reply to
Davey

Designing a "soft eject" tape mechanism?

Lightning rod holder?

:D

Reply to
Davey

Put taller metal poles with sharp spikes on top on the hills around the dip.

Colin Bignell

Reply to
nightjar

On Fri, 3 Jul 2009 14:36:58 +0100, "nightjar" had this to say:

The Furse website quotes some US study which reckons that blunt air terminals are more effective than sharp ones.

Reply to
Frank Erskine

Davey wibbled:

No - making 100+ of the bloody things (having made quite a few the previous year and they'd been in service without incident).

Now that was a boring, but well paid 3 months :)

Reply to
Tim S

Appreciate what useful protectors do. From the NIST:

How does that Belkin 'divert' without a short connection to earth? It doesn't. Which is why its manufacturer's numeric specs also do not claim protection.

When damage cannot happen, the protectors are located as close to earth as possible. A surge diverted to earth before entering the building does not go hunting for earth, destructively, through household appliances. Your telco suffers about 100 surges with every thunderstorm. They also do not waste money on protectors adjacent to electronics. Effective protection means every incoming wire in every cable gets connected to earth either directly or through a protector.

Will a protector stop or absorb what three miles of sky could not? That is how the Belkin gets recommended. That is also why your telco does not waste money on those solutions.

Ben Franklin demonstrated the concept in 1752. Lightning seeks earth ground. Since a wooden church steeple is an electrical conductor, then lightning strikes the church. Unfortunately, wood is not a perfect conductor. Therefore voltage exists. Voltage times current defined the energy destructively dissipated in that steeple. Franklin simply diverted lightning to earth - lightning rod. A conductive lightning rod means near zero voltage - energy not dissipated. Therefore energy gets dissipated harmlessly in earth.

Your solutions even to the antenna are same. You must divert the current. Energy must is dissipated harmlessly in earth. If the surge enters a building, it may find destructive paths via appliances. Protection means that current does not enter the building. Protection means energy is dissipated harmlessly in earth.

Your solution is a 'whole house' protector and earthing that both meets and exceeds post 1990 National Electrical Code. Your phone line already has that protector installed for free. Same concept also used by the telco in their every CO to have no damage. Your cable needs no protector - must be earthed directly before entering the building. Same concept. A surge that finds earth before entering a building need not enter the building.

Every incoming surge path must connect to single point ground before entering the building. For example, the antenna lead must route over and connect to that same ground before entering a building.

Fundamental to making this work is repeated by the NIST:

How good is your protector? Only as effective as its earth ground. How to make any protector better? Upgrade earthing and connections to that earthing. A protector is only as effective as its earth ground. Some solutions need no protector. But every protection solution always requires the one critical component - single point earth ground.

Reply to
westom

The idea that a surge protector csn protect againt a lightning strike is one of those misunderstandings the manufactureres only encourage. What they really do is introduce a fire risk and take your money. Agreed, and it's not just catastrophic faliure of the sacrafisial MOVs

Case in point; look at this Belkin branded power-strip that failed after a short time

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is rated for the full 13A continuous load and note how the connections to the bus-bars are properly ferruled and spot-welded, but, oh dear, look at the intervianing surge protection board,

4 blobs of finest lead-free!! These solder blobs are supposed to pass 13A continually? I_don't_think_so. Fortunately the resulting dry-joint went totally open-circuit without too much arcing and sparking.

Who agrees that a better arrangement would for the incoming cable to be ferruled and spot welded onto the bus-bar and the PCB to be connected to the bus-bars at a different point?

Reply to
Graham.

In which case, I'd use both.

Colin Bignell

Reply to
nightjar

Probably depends on if you are attempting to prevent the strike in the first place, or control its location. The pointy type are good for spraying out charged particles to help lower the voltage gradient - reducing the likelihood of a strike IIUC, and the rounded ones make a better strike target.

(you know this thread is wandering into territory that might summon you know who...)

Reply to
John Rumm

Oh dear. It's w_tom. He's back...

Reply to
Bob Eager

Too late...although he's on gmail now...

Reply to
Bob Eager

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