The average technician finds and fixes four to five split cable pairs in his career. That’s not very many, and the reason is that split pairs are not repaired until all other vacant pairs have been used, and all other faulted pairs have been repaired and used. Only when the count is full, and a pair for a new service order is needed, is the split traced.

In the old days of split locating, the split pairs were shorted in the field and tone was applied at the central office. By looking for an increase or decrease on either side of a splice or access, the split pairs could eventually be proved to a splice.

In the early 1970’s, a gentleman by the name of Bill Dudding, a maintenance supervisor for Pac Bell, using a Perkins Rapid Pair Tester, developed a method of determining the distance to a split cable pair by measuring the capacitance loss beyond the split and comparing this loss to a good cable pair that went the same distance. Today’s open/split meters still use a variation of his technique.

Split Pairs Characteristics
Split pairs are always man-made trouble. They do not occur because of lightning, squirrel bites, gunshots, war, or pestilence. They occur because a technician has incorrectly spliced two pairs. It is a completely mechanical procedure which need not ever happen.

Splits always occur in splices or accesses. They do not occur in un-entered cable.

Splits are the last trouble to be chased down, usually only when the entire complement has been used up.

A split occurs when conductors of pairs with different twists are spliced together along a cable route. Because the twist control is destroyed, the capacitive balance of the cable is affected, and the common customer complaint is cross-talk. If the pair is split for a long enough distance, the conversation on the other pair can be heard quite clearly.

There are split and corrected splits where a split pair was identified and someone corrected it at another splice. In that case, there will be dial tone on the pair but the others on line complaints still exist.

Split and corrected cable pairs that are in short distances may never cause others on line complaints in Plain Old Telephone Service but will raise havoc on bandwidth for ADSL, HDSL, T1, and IPTV.

Dealing With Splits
The most common solution to the cross-talk complaint is to cut one of the affected customers to another pair. The customer is back in service and the symptom has been treated. But, as the cut pair shows no resistance faults and tests as a good vacant pair, it will be put back in service repeatedly. This will cause further complaints from the original customer, and eventually a public service complaint.

The first man on site that is making the install will usually misinterpret the split as one side of the pair open, as there is no dial tone. With no other pairs to cut to, the problem is turned over to the Cable Repair Technician (CRT).

Using an open meter, the CRT usually finds a balanced pair, which places any open close to the far end. When measuring back from the far end, the pair still reads as balanced. The problem is finally diagnosed as a split.

To identify the split pair, audible tone is applied. The tone is identified in the count with an amplifier. The split pair mate shows more tone on it than any other pair in the count.

Now it’s time for the Time Domain Reflectometer (TDR).There are several brands of split meters available, but the TDR is the easiest to use to find the location of the split. Set the TDR to cross talk. Next, connect one set of clips to the split pair and the other set of clips to the pair that is split with it.

Set the range to the length of cable under test. A flat line will show on the screen and then there will be an up above the baseline or a down below the base line and then a lot of other convoluted information beyond that point on the screen.

Next, reverse one set of clips. What was up on the screen beyond the flat line will go down or what was down will go up. Keep in mind that all other information to the right of the first event will also change polarity. Move the cursor to the first event from the left of the screen and the TDR will indicate the distance to the split.

If multiple splices are close together audible tone can be used to identify the correct splice. Short the split conductors at one end and apply an audio tone at the other end. An increase in tone will occur beyond the splice containing the split pairs.

Identifying and fixing split cable pairs is a difficult task made easy with tone, an amplifier, and a TDR.

Signing Off
Make sure you’ve made your plans to attend OSP EXPO 2008 in Baltimore, Maryland, October 22-23. This year’s seminar lineup promises to be one of the best if not THE best yet. Stop by my booth or one of my seminar sessions, “Ask the OSP Expert”, and introduce yourself. Meanwhile, you can always email your comments to me at dmccarty@mccartyinc.com. If you are looking for onsite OSP technical training or consulting to set up processes or solve difficult trouble tickets, give me a call at 503.538.1229.