sundance-communications.com/forum Forums TDM Business Telephone Systems NEC Telephones & Systems Help! Telco line destroying my DSX40

I installed a DSX 40 today. System was protected by Panamax CO4x4 module but some faulty ring signal burned up 2 CO ports. I first noticed that one of my ports was bad and thought it was a bad out of box failure. So I switched in an unused port and all seemed OK except system wasnt responding to ringing on that line. Butt set sounded rather intense and higher in freq than usual monitoring ringing on that line. I didnt make any voltage measurements. Ringing was OK on a cheap cordless but NG on a 2500 set connected to CO. I noticed that the second port was destroyed when I inadvertantly answered the suspect line. I heard ring voltage as I answered it on a system phone. There was no indication that the line was ringing.
The destroyed ports have become shorted.
Telco will be out tomorrow to fix. Why didnt the Panamax 4x4 stop this?
Looking back this may have been the demise of their old Executone system that I was replacing. It seemed more like a processor problem instead of a trunk port though.
Whats going on? I would have thought that more protection would be built in to the CO interface.
Steve

Steve, we are getting into Watts of power dissapation. (Get it? Lots of power, Watts of power. Ah never mind, it wasn't that funny I guess) Normally, the C.O. trips the ring when the line is seized. Power load is milliwatts. 0.030 watts, hopefully less. Ringing power is going to be 2-3 times as much power, and not for milliseconds. Think about a light bulb. 110-120 VAC is the standard. Hook it up to 220 VAC and watch the FLASH! (Do this with protection from flying pieces. Look at the bulb using a mirror, or thru safety plate glass.) You are presenting the trunk interface circuit with up to 2 seconds of DOUBLE the power it was designed to deal with!
Yeah, Yeah, what about lightning. Well, the typical trunk protection works, because lightning is WAY over the c.o. line voltage and gets snubbed REAL hard, semi-instantly. AND you aren't picking up the phone just as that HUGE spike hits the system! It's all about timing and control. Hmmm, sounds sorta political. John C.

Steve, my guess would be that the telco is using some form of loop extenders that typically run the line voltage as high at 96 volts, DC. Remember that most of today's telco techs don't really care much to do the job correctly. If dial tone is there, then it must work.

I had some OPX stations where the message waiting light stayed illuminated constantly. Upon testing, we found that the line voltage was coming in at 72 volts DC.

These voltage adjustments are frequently accommodated by DIP switches or some other form of field-modification on their equipment. They really have no incentive to double check, since the problem is always in the customer's equipment.

If I were you, I'd get some true voltage measurements BEFORE they get there tomorrow. They may do some pre-testing, find their error, fix it in the CO and then show up telling you that there's nothing wrong.

Surprisingly, excessively high ringing voltage doesn't often cause problems. It's the maintained high line voltage that is the culprit.

As for the Panamax units or most other protection devices, they really don't look at tip to ring voltages. They look at line to ground voltages. Since most CO line protection devices clamp at or around 235 volts, they really didn't miss anything in your case.