phone line FREE cabling and networking Helpdesk
 Question by Bernadette Martinez posted 13 Sep 2005
 phone line
Okay, it first started when I came home and the line was dead. It took a couple of calls to the phone company, disconnected both phones till the line started working again
Now yesterday, the phone rang (half a ring) and stopped. I didn't know who it was, but that person did it again and the same result. I unplugged the phones again. I was able to dial out, but not able to recieve calls. Both phones are cordless and one is brand new (because the phone company said we needed a new phone).
Well, the man from the phone company just came by and said the problem is in our house, but didn't say where????
Is this true and how big of a job is this to fix.
 Answer by Joseph Golan posted 14 Sep 2005
Dear Bernadette,

This problem is known as "pre-trip" or an "escape short", and is caused by either a high resistance short (across the line) or a high resistance short to ground.

The voltage to ring the telephone is higher (105-110VAC @ 20 Hz) then the talk voltage (48VDC).

When the ringing voltage is sent it may cause this high resistance to lower and become a short. A short on the line is seen by the central office as a telephone going off hook to stop the ringing which is exactly what you are describing as the half ring.

The problem could be caused by a telephone instrument (answering machines, faxes, modem, and burglar alarms are all considered a telephone instrument in this case) or within your home's wiring.

Many times the problem is on the phone co. wiring and is caused by wet cable (water reduces the insulation factor of the cable construction).

I would start by disconnecting all the telephone instruments and ring the line to see if the pre-trip cleared, if so then one of the instruments is defective. If not, then you need to isolate sections of your cabling to find the cause.

If you have a box on the outside of your home where your wiring meeting the phone co's wiring (Know as a NID, Network Interface Device), there is normally a test/disconnection point in there where your can unplug your wiring and plug a telephone directly in. Run the ringing test again to prove it is in your cabling or the telephone co wiring.

A good telephone man should be able to locate and repair the trouble in about an hour, check your local paper or telephone directory for listings.

Joseph Golan, RCDD

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