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telephone line surge protection

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Telephone line surge protectors seem to typically have one socket marked "IN" and the other marked "OUT". Where does the internal side line go and where dose the external side line go? Does it matter?

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unlikely, since its probably just a fuse, and in Australia all our lines run under ground, so the chances of a surge are stupidly minimal.

 

But the line to the world goes 'in' and the line to your modem\house goes 'out'.

 

Keep in mind if you have ADSL, you dont want one of these as the 'good ones' can often have a passive EMI or RF filter which will block your ADSL signals quite well.

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Three years ago we had massive problems with the 2 lines into our house.

 

In particular my line i use for the Internet was being fed a current of 32v which the Telstra technicians said was probably due to the shorting of lines. But he said voltage on Telstra lines are very minimal,so surge protection is not warranted. With my line just glad my Adsl Modem router has internal filters ,the only real worry is when Lightning is around or a fallen line from a car accident. Most voltage is now filtered from Junction boxes and built in.

 

These Surge protectors are not worth it. Most of the Surge Protectors are based in US and European standards.

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Underground lines aren't as common as you'd think - probably common if the area is 20-25 years old or less.

And there's still junction boxes and the like that are above ground though I doubt they'd get hit very often.

 

I've witnessed the aftermath of at least 2 strikes that went through the line. Had a mate's computer here and luckily a couple of components on a PCI dialup modem got fried, once the card was taken out the computer worked fine.

 

Lots of surge-protect devices use a sacrificial gas fuse, once it cops a hit you have to replace the whole unit. I've got a powerboard with phone line + power surge-protection, the cheap ones should be like $20-$30.

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My modem blew up with lighting hit around 20m from my place. Dunno whether or not it came through the phone line or not...

 

Was looking to get the new one surge protected (both power and phone line), but it looks like the latter can be a bit problematic from what has been said. However, I might try the one built into the UPS I've got hooked up to it to see if that works :-P

Edited by nobody813

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unlikely, since its probably just a fuse, and in Australia all our lines run under ground, so the chances of a surge are stupidly minimal.

Actually no it's not. Any lightning strike can cause an induction surge in copper phone lines and underground lines are much more prone to this than overhead lines.

http://www.randolph-telecom.com/articles-faq.html has some quite good stuff.

In particular

 

http://www.randolph-telecom.com/articles/A...ion,%20Rev1.pdf

Page 3

 

The vast majority of lightning surges on phone lines are inducedon the phone line by lightning striking

something nearby, such as a tree, a building, or the ground itself. The huge currents associated with

the nearby strike generate intense electromagnetic fields that couple into the tip/ring leads by

electromagnetic induction. Since the tip/ring wires are twisted together, the same voltage is typically

induced in the tip lead as the ring lead, which is why lightning surges are typically induced as common

mode surges.

Another mechanism by which lightning appears on phone line interfaces is called “ground potential

rise.” When lightning strikes the ground, the huge currents flowing through the non-zero resistance of

the ground will cause a momentary increase in the local ground potential. If the strike is near the

point where the primary protector is connected to ground, this ground potential rise can effectively

force current up the ground lead of the primary protector and onto the phone line, sort of like coming

in the back door. Either way, a large common mode surge is induced on the phone line.

Yet one more reason for FTTH. No copper overhead or in ground so no power spikes or induced surges to fry your comms connected gear.

Edited by aliali

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The more you know!

With the 30 or so hige forked lightning strikes around my area, i wonder why I havent had any damaging surge?

 

I guess modems are built for high voltage because of the spike that occurrs if the line 'rings'

"telephone line voltage normally is 50 Volts DC when not used. Ring voltage could go up to 130 volts at 50 HZ"

 

Wont handle a direct strike; but it'd force some sort of protection ot be built into modems to begin with.

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The more you know!

With the 30 or so hige forked lightning strikes around my area, i wonder why I havent had any damaging surge?

 

I guess modems are built for high voltage because of the spike that occurrs if the line 'rings'

"telephone line voltage normally is 50 Volts DC when not used. Ring voltage could go up to 130 volts at 50 HZ"

 

Wont handle a direct strike; but it'd force some sort of protection ot be built into modems to begin with.

Just lucky I reckon. You may find someone "up the road" has taken repeated hits to their gear. It's the nature of the beast.

 

Back in March 06 we had lightning take out the top of one of our private power poles, melt the overhead wires and shatter several ceramic fuses and two bakelite switches in the old cowshed. The damage in my house about 50 metres from the cowshed was a destroyed ISDN modem and all the USB ports on the mobo dead (modem connected via USB).

Surge came down the phone line not the power line which you would expect.

Talking to the Telstra guy who replaced the modem he said he had seen strikes in towns where houses for a block or so around the strike point suffered no damage but one house several blocks away had all their telecomms connected stuff taken out, phones included.

The vagaries of the electrical path I assume.

 

Posted Image

The bottom left white fuses fuse holder was on the ground in two pieces. The two right hand top row ones holders where in small fragments. The switch bottom right was also in bits and the one to the left of it whilst looking intact had all the contacts melted.

On the other side of the wall an electric fencer was blown off the wall and it's power point destroyed. Yet the other fuses and switches where fine. As where the milk vat and vacuum pump electric motors, the hot water heater and the water supply pump at the other end of the power line. Now got UG power out to the pump house as it was only a few hundred more expensive than replacing the damaged pole and overhead wires. BTW the pole had a metal cap on it to stop water getting down the end grain of the wood and rotting it. Found that about 20 metres from the pole with a nice hole burnt in it.

Probably lucky a fire didn't start in the pole or cowshed.

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Wow. thats some impressive damage.

 

Also reminds me of the story my Dad was telling me, about using 3Phase welders on 1 Phase power in the 60's.

Apparently they just DIY'd a connector, and replaced the fuses with huge galvanised nails.

 

After they blew the 3rd telephone-pole-top transformer in a week; the energy companty caught on.

 

And no, they didnt get in trouble; being industrial area, the company decided to provide proper 3phase, lol.

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I've had an ADSL modem/router fail following nearby lightning strike - everything else survived so I assume it was phone line related. I've now wired the incoming phone line through a surge protector and haven't noticed any impact on ADSL performance.

 

I've been looking into having surge protection added to the junction box as it is a lot more cost effective than installing surge protected power boards around the house.

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