Why telephone sets are immune to lightning strikes?

william chan

This question has been on my mind for some time now...

Why modems, routers and most equipments are prone to lightning strikes from the POTS lines but the classic telephone set itself is very resilient in surviving such strikes?

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
www.fd.com.my
www.mercedes.com.my

Mike Green

Think about the components in a "classical" telephone set. There's a ringer that consists of just a coil of wire and a bell with a striker. I think there's a series capacitor, but those can be made very robust, particularly when there's room for a large component. For the handset, there's a carbon granule microphone and a dynamic earphone, again consisting of just a coil of wire. The phone also had some lightning suppressors ... some kind of varistor, but the physical size and scale of the components made it less fragile. You could probably make a modem using vacuum tubes, 1/2W resistors, and large ceramic and mylar capacitors with 600V+ ratings, air gaps between components and wires that can be seen clearly with the unaided eye. That would be much more resilient to lightning strikes than current equipment. You can also design in much better protection than in most consumer equipment against lightning strikes using modern components.

william chan

Modern telephone sets are all IC based, yet they are still very immune to lightning.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
www.fd.com.my
www.mercedes.com.my

Mike Green

Again, it all depends on how you design the equipment. It's quite possible to design modems, routers, etc. to be resistant to lightning strikes or EMP damage, etc. It adds to the cost which is why most equipment has very limited resistance to lightning or other large voltage spikes, like from large (industrial) electric motors starting up.

pharseid

· At the business I work for, the phones in our old plant use to go down almost every time there was a thunderstorm. Back then we had a "phone system", today we just have phones which seem to hold up pretty well.

· On a similar note, when I was a kid, there was a nearby lightning strike and a shower of sparks came off the phone. It still worked OK afterward.

-phar

jmalaysia

One reason is that many of the external devices are plugged into AC power, which introduces power surges and blows out the low voltage DC stuff in the equipment. Another is that whole "path of least resistance" stuff. A twisted pair phone line is "open" when you aren't actually using the phone, so the path of least resistance probably will not be up one leg of the phone line, through the phone, and then to ground through the other leg. And yet one more reason- phone circuits have surge/spike protection all over the place, so although YOUR phone didn't get hit the line MIGHT have been hit.

Dave Hein

There are two ways that an electonic component can be zapped.· One way is for a power surge to cause an over-voltage in the power supply.· A surge protector will help to reduce this.· The other problem is a voltage spike on the transmission lines.· If the input transisors are not properly protected they will get zapped immediately.· Even a static electric discharge can zap an input transistor.· This happened to me when I was checking out the CAT-5·wiring in a new house I was having built.· The brand new carpet made a great static electricy generator, and I manage to zap the LAN card in my laptop computer.

The older non-electronic phones were definately more rugged than electronic phones.· I have collected some antique phones from the early 1900's, and the basic technology remained the same until the introduction of touch-tone phones in the 60's.· I believe that the junction box on the outside of the house contains a fuse to handle lightning strikes.· This may only be in rural areas, or in areas where the phone lines are above ground.· When I was a kid, I remember the box cover being blown off a couple of times by lightning strike.· The cover landed about 50 to 100 feet from the house.· My parents always told us not to use the phone during a storm, but my brother was talking on the phone when one of the lightning strikes hit.· He ended flat on his back, but with no permanent injuries.

Dave

·

steve_b

Something else to add to the equation is the density of transmission/phone lines in your area.
I've installed equipment at airports....your big city international airport doesn't usually qualify, but smaller airports tend to be on the edge of town where there is usually a very modest number of lines running to the airport....if the lightning (if = when) hits the line in a dense area, it's got more ways to disperse/diffuse, but in a rural area it'll tend to do some damage.
(we replaced many modems and the odd power supply because of this)

My boss used to live at the end of a long country road....his was the only phone on the line for a few km's. They had a rule that they'd wait for the 2nd ring before answering the phone! I was there when a lightning storm went through and the phone rang a number of times ( all single rings) and the lightning hit a fence post 50yards away (I hit the floor)....

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
<FONT>Steve



What's the best thing to do in a lightning storm? "take a one iron out the bag and hold it straight up above your head, even God cant hit a one iron!"
Lee Travino after the second time being hit by lightning!

ST

Short answer - Lack of Silicon Integrated circuits. If I recall correctly Vacuum tubes - the predecessor of the transistor was fairly immune to electrical and magnetic impulses also.

pwillard

A lot of industry telephone gear has spike protection built in... but I·think some of the cheap consumer stuff either don't do it right or don't bother with it in an effort to keep down costs.

Honestly, even a POTS phone from the 1960's that are bui;t like battleships·will not survive a direct lightning hit and still look pretty.· It's a matter of voltage induced·into the phone pair·from a nearby strike which would cause surge spike on the wire pair.· The thing is... compared to other sources and ground paths, the telephone· does not offer a really nice path to ground when compared to all the other·available paths... like the·ground wires·on the telephone poles or in above ground boxes.··Having a·better path NOT close to your NID means that the pair that runs to your phone or DSL gear·is spared death... IF it can survive the spike of the induced·surge voltage.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔


There's nothing like a new idea and a warm soldering iron.

MSDTech

Unfortunetly, my experience with newer phones has not been as lucky. I have several phones that ceased to function after thunderstorms rolled through. I will say, I feel much safer with the new cordless phones during a thunderstorm, at least they have a respectable air gap for protection.
pwillard, what type of car is that?

pwillard

I'm not saying I've never lost gear to a lightning strike.··Lost at least 3 phones and· I once lost the RF input on a TV via the cable tuner box after a storm.· TV worked fin as long as I used it as a Composite Monitor.



The CAR is my favorite toy.· It's a 2007 Saturn SKY I've had about a year and a half.· Also known as the OPEL GT in europe.· Loads of fun to drive on the· curvy·North Ga Mountain roads·near my home.



▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔


There's nothing like a new idea and a warm soldering iron.

LoopyByteloose

This reminds me of why cowboys would never relieve themselves on a fence post. The barb wire fencing can carry an unseen and unheard lightning strike for 20 miles or more along the wire.

In truth, in the early days of telephone, people were far more aware of lightning playing a role in electricity. After all, Benj. Franklin was a major contributor to the field with recognizing that electricity had polarity. He may have gotten lightning rods popularized to.

So, the phone companies had to deal robustly with the perception that any telephone might be potentially lethal. The service had hefty protection and a lot of redundant protection. These days, we just let the chips fry.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
PLEASE CONSIDER the following:

Do you want a quickly operational black box solution or the knowledge included therein?······

···················· Tropically,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

Phil Pilgrim (PhiPi)

We don't get much lightning here in the Northwest, but this thread has got me paranoid. 'Looks like it's back to basics...

-Phil

LoopyByteloose

Frankly, I wish I had an older phone. Here in Taiwan, I cannot seem to buy a basic handset that is rugged. The one I have is very cheap and volume performs poorly. If I spend more money, I just get more and more features - not more quality. And of course, I have to buy my own handset these days.

Whenever I get back to the states, I plan to pick up an old heavy touch tone. Weight is another problem. Whenever I pick up the handset, the rest of the phone goes on the floor.

Traditionally, the telephone lines had spark arrestors where they entered the building. Some of these were simply pairs of sharpened points that allowed the lightning to jump to ground. But I don''t see anything like that in Taiwan -- not sure what they do to arrest lightning.

Heater.

Are there still people out there using a phone plugged into the wall?

Leon

I do, it can be a lot cheaper.

Heater.

Here in Helsinki I last had a land line phone in about 1998. I have not seen one in a home since about then.
Many businesses seem to run without one.
All the public telephone boxes were removed throughout Finland some years ago.

localroger

The short answer is, phones are not immune to lightning.

The longer answer is that lightning has to follow a path through a device to ground in order to effect destruction, and as jmalaysia suggested it's just not too likely that the path of least resistance will go up the tip wire, through your phone, and back down the ring wire when it could just arc over at the box outside your house. And older phones contain only passive components, which are less likely to be destroyed by a short burst of energy. I have heard of newer phones, especially the more complex ones that need AC power, getting destroyed by lightning.

bill190

Back in the 1960's, telephones used 3 wires rather than two. Red, green and yellow. The yellow wire was connected to ground.

Then they stopped connecting that yellow wire to ground and ran just the green and red wire into the house. I think they (Bell Labs) figured out that it was best to NOT provide a path to ground inside the house!

FYI - The green and red wires are called "Tip" and "Ring". This is from the days when they had telephone operators who connected your call by inserting the following into the correct connection hole...

LoopyByteloose

3 wires? Where abouts? Back in the 1960's in the USA, telephones had 4 wires - red, green, yellow, and black. I was told that J. Edgar Hoover required the other two for phone taps.

PJAllen

POTS is tip and ring, red and green, always has been.
"Hoover required". ??? In his role as telephone gauleiter or what? Get real.

Cellphones suck because they only do half-duplex, you can't tell the other party to... "stop already"... till they take a breath.

Mike Green

The yellow and black leads were used for either of two purposes ... 1) to provide power for various accessories provided by the phone company, usually from a "wall-wart" somewhere in the house or office. 2) to provide a second pair for two phone line houses.

bill190

Here is an old phone wiring diagram. See in the middle section on the left where it shows Inside Wiring: "Ring R, Tip GN, and To Earth GND Y"
http://www.telephonecollectors.info/index.php?option=com_docman&task=doc_download&gid=2093&Itemid=2

bill190

Here is a picture of an old 3 wire telephone wire (red, green, yellow) with the yellow going to ground at the telephone protector. (And that was what the inside telephone wire had. Just 3 wires!)

K2

william chan wrote: »

...modems, routers and most equipments are prone to lightning strikes from the POTS lines but the classic telephone set itself is very resilient in surviving such strikes...

I had an engineering professor who told the story of how he was hired by Bell Labs to design a spring clip to hold an inductor in place on the PCB of a telephone. (His account of the design process was absolutely fascinating!) If Bell would hire a PhD just to design a spring clip, imagine the scrutiny everything else received!

No one today could afford to take that kind of approach.