Telephone protection circuit needed

In the recent ice storm, the 4800 volts from the power lines crossed over into the phone lines. It burned out many circuits in our area. It also fried some modems and phones in my house. Surprisingly, two connected modems survived. These were both protected by whatever surge protection circuit they put in a UPS. But it had the side effect of burning out that circuit in the UPS, so I cannot use that again.

Rather than protect phone equipment piecemeal, I would like to protect all phone equipement in my house using one circuit that I put at the entrance. I would like to use a fuse. I gather that most commercial "surge protectors" do not have fuses, but I think they might be a more reliable protection than varistors or whatever they put in those commercial units. Has anyone done this? What sort of current limit should I set? I guess the ringing with a maximum number of phones connected would be the upper limit. But a fuse might not be enough. What about a crowbar circuit? Is it possible to detect an overvoltage condition with an active circuit and then short all lines to ground through some fast-acting power FETs downstream of the fuses, just to make sure the fuses blow right away? I don't mind replacing some power FETs and fuses in my own custom circuit once in a while if it means I won't have to replace modems and phones. I know ice storms and downed power lines are my focus right now, but I am also looking toward spring with lightning will be the major risk.

Robert Scott Ypsilanti, Michigan

Reply to
Robert Scott
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On Wed, 24 Jan 2007 18:45:31 GMT, ---@--- (Robert Scott) wrote: [snip]

I haven't done any surge suppression/isolation active clamping circuits yet... I'm guessing some electronic process like:

1)Slow down the voltage surge risetime (If not slow already from line inductance) to give a slow crowbar cct a chance to react 2)After the fuse blows from the crowbar cct., there's now a big spark gap for cct isolation 3)Find some place to dump surge energy ...another spark gap?

Without looking, I'll guess this is a well beaten topic. Check achieves. D from BC

Reply to
D from BC

Well, I had some melted 22-gauge wire. A 500 ma. fuse would have at least protected that wire.

Robert Scott Ypsilanti, Michigan

Reply to
Robert Scott

phone

condition

blow

From past experience, in a protective configuration where you have a 'fuse' protecting active components it is the silcon/germanium/whatever that protects the 'fuse' and fails first. Read what is time response of fast fuse against overcurrent percentage. Interesting!

Stanislaw

Reply to
Stanislaw Flatto

phone

varistors

condition

blow

custom

I've designed some crowbar fuse blower circuits that circulated >100A thru a 5A fuse... now you see it, now you don't ;-)

You have to be very careful with the foil pattern on the PCB to avoid it being the fuse ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

4800V is a whole lotta volts. If the fuse is long enough that plus a huge MOV could have saved the day. Long in order to avoid arcing over. Of course the fuse would have to be mounted in a way that things don't arc over to any place that could ignite and burn down the house.
--
Regards, Joerg

http://www.analogconsultants.com
Reply to
Joerg

This isn't going to be a PCB. It is a one-off home-made thing, hand-wired. I was going to use wood for the base, but with all this talk about arcing over, maybe I ought to use plastic.

Robert Scott Ypsilanti, Michigan

Reply to
Robert Scott

into

Part of the problem is the voltages involved in normal phone operation. You have to protect against faults, but still allow ring voltage, reverse battery, etc...

There are many providers of Telco protection equip. A great many of them rely on MOV's or Sidactors. The problem with MOV is they have a limited lifetime. They work perfectly for a long time, show no signs of wear, and then "poof!": One day they're "Dead & Gone". No warning whatsoever, so they're hard to RELY on.

Gas discharge tubes also work, but they are slow (and probably would not have helped you.) Actually, I wouldn't be surprised to see the phone company replacing a bunch of these!

Active circuits are going to void any chance of continued compliance with FCC Rules Part-68, unless you want to go through the testing & certification procedures.

You can always just wind the tip & ring (22 ga) around a pencil. Cheap & dirty but it does help.

10 turns or so ought to work wonders. (For lightning frequencies, not too sure about 60 cycles)

now -- I'd consider myself "lucky"!

-mpm

Reply to
mpm

Reply to
w_tom

On a sunny day (Wed, 24 Jan 2007 23:52:44 GMT) it happened ---@--- (Robert Scott) wrote in :

Maybe not. the _length_ of the fuse, that is how many volts it will stop before flash-over is also an issue. Lightning will jump a across meter distance if iit feels like it, seen that.

Reply to
Jan Panteltje

Actually I did have something like that. It was made of enamelled wire wound around a ferrite torriod. I don't know if the inductance helped, but a short did develop between tip and ring through the enamel, which welded the copper wire together. But that short may have helped to protect a modem that was downstream.

Robert Scott Ypsilanti, Michigan

Reply to
Robert Scott

I've designed a 4A SMD fuse blower that circulated 150A and blew some SMD fuses in 15uS. The others reformed into resistors and limited the current to

Reply to
Harry Dellamano

On a related topic, I know gas discharge tubes exist for the purpose of overvoltage protection, but I was wondering what could be done with an ordinary air gap. I seem to recall hearing somewhere that no matter how close you place electrodes in air, you cannot reduce the arcing voltage below a certain theoretical limit that has something to do with the voltage required to ionize air. (which is why they use gas discharge tubes). Can anyone validate that concept for me?

Robert Scott Ypsilanti, Michigan

Reply to
Robert Scott

Robert Scott wrote: ...

phone

...

I've posted a schematics of a phone line protector in a.b.s.e,

Subject "phone line protector", Message-ID:

I've designed this to produce a very low impact on the ADSL signal.

The (constructive) feedback / remarks are very welcome.

Thanks.

-- Andy

Reply to
Andy I.

phone

Excuse my ignorance, but what is a.b.s.e. and how can I look at your schematic?

Robert Scott Ypsilanti, Michigan

Reply to
Robert Scott

phone

OK, I found it. It is in alt.binaries.schematics.electronic

Thanks for the hint.

Robert Scott Ypsilanti, Michigan

Reply to
Robert Scott

phone

sounds like a binaries newsgroups a.b. would be alt.binaries., perhaps the s.e. are sci.electronics?

Reply to
AZ Nomad

phone

I should have expanded, sorry about that, I meant the "alt.binaries.schematics.electronic" newsgroup.

A few comments:

- As with any such circuit, a good ground connection is fundamental, it goes to the pin 2 of the CN1 connector. The other two pins of CN1 go to the phone line, the home phone equipment is connected to CN2.

- One should probably aim at a higher voltage rating of the fuses F1 and F2.

-- Andy

Reply to
Andy I.

Given your location you need at least two stage protection. First stage is lightning type telephone line protectors. The second stage should be what is called a 5-pin (replaceable) protector. You should be able to find them easily with Google.

--
 JosephKK
 Gegen dummheit kampfen die Gotter Selbst, vergebens.  
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Reply to
joseph2k

Protectors are not protection. Shunt mode protectors become conductive only during a transient. They do not stop or absorb surges. They make a temporary connection (a shunt) to protection.

Reviewing the schemtic posted by Andy, those fuses also do nothing useful for a 4800 volt surge. Fuses are only rated for 600 volts - remain conductive when trying to stop many thousands of volts. So what provides protection? A protector that connects to earth; a shunt to earth so that a surge need not find earthing connection via household appliances.

What is two stage protection? A system that has layers of earthing. Same exists with AC electric. 'Whole house' protector installed in a mains box makes a short connection to building's earthing electrode. That is secondary protection. Primary protector provided by the utility is demonstrated in pictures in:

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Meanwhile, the telco installs a 'whole house' type protector on all subscriber lines where their wires meet a homeowner's. Again, this protector is only as effective as its short ('less than 10 foot') connection to a single point earthing electrode. A protector installed for free because it is so effective and so inexpensive. A protector often unknown to those who somehow want to stop or block surges (ie those fuses). Surges are not stopped or blocked. Anything that would do that stopping is already inside phone appliances. Surges must be diverted to what surges seek. Either a surge is earthed before it can enter a building OR surge will seek earth ground destructively via household appliances. So that protection already inside appliances is not overwhelmed, the effective protector makes that short connection to earth.

Telco install that device, for free, in the NID. A protector that is only as effective as earthing provided by the homeowner.

Reply to
w_tom

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