Trunk Failure on BCM's 50/200/400

[NewTechinTown]

Have this nice informative memo from Nortel explaining that high ring trip currents are causing damage to analogue trunks in just about every Nortel switch. They say that they recommend a 200 ohm 1 watt resistor to correct the problem but they dont mention anything about the tolerance level. Any info would be helpful.

 

[acewarlock]

I would use Mil Spec +/-1%. Where does the Resistor go, across the Tip/Ring?

 

[NewTechinTown]

They say they advise using them on tip and ring. Were familiar with the problem, just new to the solution.

 

[hawks]

Not sure of the part number but Nortel has a cable that they made for this problem.

 

[endlesswinter]

Hawks,

I thought this cable was only recomended on lines that had higher than the recomended current or voltage specs. do you use these on all installs?

 

[NewTechinTown]

hawks: I know they make a cable but I dont think its in mass production yet. They only sent so many out to Authorized Nortel Vendors.

endless winter: You should "only" use the cable or resistors if a problem is present. If you're not experiencing problems you should'nt modify the lines at all.

 

[hawks]

NewTechinTown you are correct I just thought maybe you could get one from your Vendor. That way you could look at it, maybe take some measurments and see exactly where they put the resistance.

endless winter: No like NewTechinTown said Nortel only says use the cable if there is a known ring current problem.

 

[riteeh]

I have one line that physically damaged a trunk port on my GATM8 module and I had to order a replacement. Is anyone aware of a way to determine if this is a problem with all my lines or just a few because I don't want to kill another trunk module, nor do I want to install unnecessary resistors across all my lines (We have 2 GATM8 modules, 2 BCMs, and 16+ lines between the two of them). Some trunks are on GATM8 and others are on the BCM itself. Does the resistor "fix" work for both?

 

[CBasicAsslember]

Putting the resistors "across the Tip/Ring" doesn't make any sense as it would take the line off hook. The best description of the problem is in version 2 of the memo.

When a line is answered (goes off hook) while it is ringing, the ringing signal continues to be present for a short period of time until the Central Office (CO) detects that the trunk has gone off hook, after which the ringing signal is removed.

In some circumstances the energy available from the ring signal is large enough to damage the front end of the trunk port. There are 2 ways to reduce this energy, limit the voltage or limit the current. The easiest and least expensive way is to limit the current.

Temporary solution in version 2

If the loop length of the service to the customer location is less than 2 km, the installer can install 200 ohm, 2W current limiting resistors to tip and ring of each analog trunk as a preventative measure before the system is installed. The BCM50 must then be configured for medium or long loop length after the resistors are installed to compensate for the reduction in voice signal.

In electrical engineering terminology current limiting resistors are assumed to be in series. If the resistors were in parallel one would refer to them as current shunt resistors. The resistors go in series with tip and ring. The reason for not needing resistors for loops in excess of 2km is the series resistance of the wire is large enough to limit the current. IOW, the 200 ohm resistors are a substitute for 2km of wire resistance. I suppose making it simple by recommending two resistors placed in series with tip and ring would not be bureaucratic enough for Nortel.

I wouldn't worry to much about the tolerance, 10% would be fine, 5% are probably easier to find.

 

[acewarlock]

But Nortel need's to make there $75.00 for the 2 Resistors and piece of wire, assesmbly and packaging.