Telephone line surge protection

I have to assume a standard, set of twisted pairs, shielded, and grounded at many locations phone cable. Now, that is quite a mouthful, but it is a sensible, standard starting point of discussion. IF not, fix it. Otherwise:

Since your cable is looong, it is an antenna, ready to pick up energy from a nearby lightning. Nearby, I mean a few miles away. There is no avoiding of that. So. make it sure, that the MOV (metal oxide varistor) protection on BOTH end of it is in place. Othervise, you are in trouble. If you have a section of the line without shielding, you are in double trouble with the antenna factor. Heavy duty MOV protection between the lines and against local ground is your solution. The price is, that DSL (higher frequency) transmission may be in trouble.

It has been a good 20 years or so since I have been into this, but back in the olden days (in the US) a RING signal was something like 200 VAC at 20 Hz. I would make sure that MOVs had a rating above this voltage otherwise you might not get many incoming calls. Also in the US, telephone equipment has to meet FCC Part 68 specifications before they can be connected to phone lines. I would expect equipment meeting this spec to handle your problems for you.

Of course my info is 20 years old, and I have no idea where you are located.

Sincerely

Bill

Your cable has a metalic shield that is used for noise mitigation and protction from voltage surges. I hope your cable is attached to the same pole line as your power so that this shield can be bonded to the power ground. Also, is your service drop long? This is the line that comes from the terminal at the pole (if it is aerial) to the protector on the side of your house. This needs protectors at the cable terminal if it is over several 100 feet long. Also check to see if the power, telephone protector and cable TV (if you have it) is all bonded together at the power meter ground wire

John Wallace

Atlanta, Ga
Bellsouth Tech Support

Thank you John!!

Reading your post got me thinking about some other potential problems too. If he has extended his service... say from the house to an out-building... The phone cable one buys at your typical hardware store is NOT shielded. It is typically two pair only. This leads to another potential problem. [Red and Green] wires make up one twisted pair. [Black and Yellow] make up the other twisted pair. One should keep the pairs together.

I noted in our house when we moved in that it was wired for multiple lines. We had two active. In our case [orange , orange/slate] made up one pair, and [blue , blue/slate] made up the second pair... or generically, [any color, any color/slate] constitute a pair. I added this bit of info because someone adding a phone in a bedroom might come up with the discrepency... and again, one should keep the pairs together. When wiring a pair into an RJ11 (phone jack), wire the pair to the red and green wires and ignore yellow and black.

John, since you are professional at this, feel free to critique the above info. I only know it works for me... I am forgetful though. I can't remember which is TIP and which is RING.

Also, with the roller coaster ride phone companies have undergone over the past few years, is part 68 still in force??

Sincerely

Bill

More thoughts...

He might want to check his battery voltage across tip and ring (red and green). It should be approximately 48 volts DC. If it is significantly more, that could cause equipment to smoke.

Also John... why not join us. You could be quite helpful, and it is alot of fun... although CR4 can be quite addictive.

Bill

And yet another thought.

We currently are using the cable company for phone service. They generate battery voltage (-48 volts) on site. If someone were to switch from cable back to telephone company AND were to miswire the connection, might it be possible to get the local 48 volts PLUS the TelCo 48 volts for a total of 96 volts? This might fry front ends.

Bill

There is a standard module (the name of the standard escapes me now) to connect anything - phone, modem, DSL - to the phone line in a standard (there is a surprise) way. It have to provide the standard impedances and standard MOV protection to provide a "reasonable" protection from induced voltages into the cable hurting you. What generally is not discussed, that in the blockhouse serving you and owned by the phone company a similar protection circuit has to be working too. You do not have to design anything as such modules are available off-the self. What you have keep in mind, that these - like anything else - can fail.

Hello Martins73,

Please consult your local PSTN and work closely with the switch and field technicians to solve the problem.

From your qury, I suspect grounding problem.

The team must check to confirm the status of the grounding at the exchange switch and MDF, the loop between exchange and the last mile pedestal (DP) and at your premises, the LP.

Again the PSTN should be able to advise you on the standard telephone line set to use.

Remember also, that lightning may occur without any flash so may not be noticed except on its effect on equipment.

Best of luck.

Cheers,

Ethobil

Are the telephones newer solid state or the old style? Solid State circuits could be possibly be damaged by static charges on your body if the humidity get low. A good can of static spray will help all the electronics survive.

Also check for a problem between the incoming telecom wires and ground to see if there is some sort of "ground loop". I once had a bad neutral in a plug and wound up replacing two Ethernet cards before I found the problem.

The MOV's are a great start, place one across the line and one on each leg to ground. Just make sure of the voltage like one of the other responders mentioned.

Any items with coils (motors, fluorescent lighting?) being switched on and off? Place MOV's on them to prevent back emf from being a problem

Sciesis2, Yes the Red, Green, Black and Yellow Inside Wire (IW) is also called Quad wire. The problem with it is there are no twists to the conductors that make up a pair (Red and Green one pair and Yellow and Black the other pair) so it is prone to pick up a lot of impluse noise. Also if both pairs are working you will get crosstalk when both lines are in use. Now none of this has much to do with the voltage surges though. Here in the Southeast ( old BellSouth territory now 'the new AT&T' ) we use at least Cat 3 cable for IW. We also place solid state protectors at the house where we terminate the drop and attatch the IW. The bond to the power company ground rod is also connected here. BTW, the ringing voltage is usually 110Vac, 20 Hz superimposed on -48Vdc.