*TOTALLY* isolating phone from line, electrically?

I've never heard of one, and I can think of several reasons why not right off the bat.

Telephones use several different types of signals for different purposes. They use high voltage, low frequency pulses for ringing, there's an offhook voltage, and there's an onhook voltage. A device that you would create in order to do this isolation would need to somehow process those signals, isolate them (perhaps, no, probably, using optoisolators), then regenerate them on the house side.

The regeneration would require power.

The power would come from... say it with me... line current.

Which lightning could cause surges in.

No more isolation.

Also, lightning could easily fry the circuit before the isolation, and arc across the optoisolator pins, frying the internal circuit. So, now, instead of having one point of entry (assuming the phones aren't powered, which is a really poor assumption these days), you have two.

The only real way to isolate telephones from the external network is to pull the plug, or perhaps include a heavy duty switch that gets tripped when lightning is detected (heavy duty enough that even if it gets a near direct hit by lightning it won't arc, though the EMP might fry things anyway...)

--Russell

--
It was a trojan now it was identified that it was that machine the trojan
was not identified but it was identified as being that machine.
-- Jamie the spammer, 10/29/2003
Oh, and I still have connectivity.

info.

I didn't read the whole thread, but have you looked into whole house surge protectors. They can be professionally installed into your breaker box and protect both the power lines and phone lines (and sometimes even the cable line).

Harry

-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----

- The #1 Newsgroup Service in the World!

-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

I believe you are confusing the National Electrical Code with lightning protection. The NEC is written only for the purpose of human safety. It makes no effort to address transistor safety. The most common source of destructive surges - indeed the shortest and most direct path incoming to electronic appliances - is AC electric.

We still build new homes as if the transistor did not exist

- even 30 years after the transistor became ubiquitous. However, telephone connections inside the typical house is made via a 'whole house' surge protector - provided free by the telco. You can find yours in a box, often the NID, located (by code) within twelve inches of where the wire enters your building. And, of course, that surge protector is only as effective as its earth ground meaning that 12 AWG (or larger) wire must make a less than 10 foot connection to earth ground.

Again, the code is only concerned with human safety. Therefore the code says that ground wire must be less than 20 feet. But for effective transistor safety, that wire must be less than 10.

Posted elsewhere in this thread is much more information. Must of which will be in direct contradiction to so many urban myths - and yet was standard knowledge even before WWII. For example, your telco connects a $multi-million computer directly to overhead wires everywhere in town. Do they disconnect for thunderstorms? Or do they stop service for three days while they replace the $multi-million computer? Of course not. They too use simple 'whole house' protection methods. All incoming wires are first earthed before entering the building - either by direct connection or via a surge protector. Earthing - not surge protector - being the 'magic' solution. Earthing techniques so long and well understood that we should be building all new homes using Ufer grounds. Again, a technology probably long older than you - because effective surge protection was that well understood for that long.

Benchmark in surge protection is Polyphaser. Their application notes are considered legendary. What do they discuss? Their products? Of course not. Polyphaser is selling effective protection. They discuss earthing ... extensively. A surge protector is also only as effective as its earth ground.

Phone line appliances such as phones and modems already have the galvanic isolation you are seeking - typically rated at

2000 or 5000 volts. So why does damage occur? That protection that also exists in computer power supplies and most every other household appliance assumes the building has a 'whole house' protection system. Something not required by any electrical codes. If the 'system' does not exist, then an incoming surge will overwhelm internal appliance protection - seeking earth ground, destructively, via that appliance.

Even Home Depot sells effective 'whole house' protectors for residential AC electric - > OK folks, here's a little something that just blew through this

In the end the only really good insulator is distance. If lightening can arc from a cloud to the ground it can jump a few inches and bypass any black box you can invent. It just takes enough voltage.

Having said that.... perhaps you could build something using fiber optics. You just need to decide how long a length of fibre you need to seperate the two ends of your black box. (and solve the power supply problem others have pointed out).

Go to

They specialize in lightening protection products and have them for telephone and datacom applications.

arc

box

the

have

You could use a cell phone, albeit with possibly reduced throughput.

Ken

How does computer or telephone get electricity if it only connects to outside world using a fiber optic? Why recommend a high tech, expensive solution when effective protection methods are so effective, so less expensive, and proven in most every town every year for generations? The basic concept is called earthing - as Polyphaser application notes make woefully obvious.

Early ham radio operators would suffer damage from lightning. They would even disconnect the antenna and place it inside a mason jar. They still suffered damage. Disconnecting alone did not stop damage. Distance alone (and that mason jar) was not sufficient. Then they earthed the antenna. Suddenly damage stopped happening. Of course. That is the principal behind well proven protection - without fiber optics.

Any wire that enters the building must first connect to central earth ground - as Polyphaser so repeatedly demonstrates. The important distance is the one to earth ground. Not farther; closer. Connection to central earth ground typically must be less than 10 feet. Some wires can be connected directly to earth ground (cable and satellite dish). Others must make that central earth ground connection via a surge protector.

Noth> In the end the only really good insulator is distance. If lightening

It might look that the telephone line get the lightning into house, but thigns are not as straighforward. What kills the device connected to the telephone line and the mains power is the huge voltage difference that happens between mains power and telephone line. This voltage difference can be cause by either:

1. Lightning hitting the telpehone calbe, telephone central office where the cable goes or nearby the central office. This causes the telephone line potential to raise
2. The lighting hits the electrical distirbution network. Your whole ground potential in your house raises to very many kilovolts This causes the voltage difference between the telephone wires that are grounded on the one end at the telephone central that is still the original ground potential (no raise there)

It is the combination of mains connection and telephone connection that causes the msot disasters.

The telephone modems are already isolated somewhat (1.5 - 4 kV osolation). This is not enough for ay real lighting protection. Ýou need a very high isolation to make the isolation work. There are some special products that convert telephone line to fiber and back, that could help in some this kind of cases. Quite expensive special solution.

Usually the good enough protection can be made with proper whole house protection plan, where there are surge protectors for mains and telephone line, and both of those are connected togerher and wored to good ground connection. This kind of arrangement usually limits the voltage differences to something the equipment can handle.

Here is one isolator:

It promises up to 75,000 Volts isolation (4 inch air gap).

Here are links to some other products:

The existing products on the market I mentioned are from around

370 USD and up.

--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/

A normal PC definately needs the mains power connection or it needs to be a laptop running on batteries.

If the device is very low power device (just uses milliwatts or tens of milliwatts), then it is possible to feed power to it optically through fiber optic cable.

Ot use it off the solar panels from room lighting.

Proper earthing combined with right surge protectors is a very good solution for this.

You are right.

--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/