Copper Line Testing

Testing of copper lines can be performed in a number of ways. The exchange buildings (now Central Offices) have Test Desks normally located close to the MDF. The engineer would go to the MDF and insert a patch cord into the connection block for the line to be tested. This would divert four wires back to a jack socket on the Test Desk. The technician would then return to the desk, plug a cord into the jack socket and connect the large meter to the circuit. He would then manually perform a series of tests looking out of the exchange and into the exchange. An experienced engineer could use the meter to check capacitance and tell from the flick of the meter needle if it was a phone or line fault. Repair engineers would then be dispatched to fix the fault.

Another method would require the engineer to attend the site with a voltmeter and perfom the same series of tests but directly from the MDF frame or another distribution point along the circuit. This may have involved opening street cabinets or climbing Telegraph poles.

In complicated fault scenarios the two engineers would work together to isolate a fault on the copper circuit. This would then include sending tones out down the line or the roaming engineer putting a 'short' or 'diss' on the line. A short circuit would prove the line was okay to the remote engineers position, a disconnect may remove a strange condition such a earth or loop and direct the engineer to go further out along the line or closer back to the exchange.

In the photo you can see the patch cords plugged into the sockets and also the key switches (next to the dial) that the engineer used to manually select a pair or single wire to test.

Test Desk used for Copper Line Test

 

Automated Copper Line Testing

Advances in technology and a reduction in engineering staff has changed the testing methods now used. Although the engineer may still go out with test equipment it is now less often and only when really necessary. These so called 'Truck Rolls' are time consuming and very costly. The focus is now on accurate fault diagnoses and sending the repair man to the right place, this reduces cost and OpEX (Operation Expediture), decreasing spend and increasing profit.

Testing Copper Lines can now be automated using Test Access Switch Matrix (TASM) - also known as Test Access Matrix (TAM). TASM equipment is installed in the central office and connected into the line circuits. There are several TASM manufactures, one of the biggest being UTEL, this company supplies variants of Test access from rack mounted units catering for 400 circuits to DSLAM modules managing just 1 port.

The TASM switches the selected line circuit to a common test bus which is connected to a Test Head. Control of the TASM is usually carried out remotely, the Customer Services department will simply choose the phone number to test and the internal company systems handle the details of what to switch and where. This means that staff require no knowledge of the telecoms infrastructure and if the Test Head returns sensible results the job can be de-skilled and the wages cost reduced.

Test functionality will depend on the test header vendor and both functionality and cost vary greatly between products.

 

 

TASM / TAM Installed

Default TASM State

The TASM / TAM is incorporated into the line circuits. The default or normal mode is switched through. The unit is typically not powered unless switched so the relays are in a normal state and connected through to ensure the customers line is not broken if the power fails.

The TASM / TAM output varies depending on the customers requirements. It can be output on two wire or four wires. Four wires is a better option but some test heads can only handle two wire inputs.

The physical location of the TASM / TAM is dependent on the space availability in the exchange / central office and the type of TASM / TAM deployed. Some units are supplied inside a dedicated rack with structured cabling and layout schemes. Smaller units can be fitted inside existing equipment where space allows.

 

Copper Line Test using TASM or TAM
   

Test Line

The TASM/ TAM switches the A and B lines of the 'Line' side forcing the two wires to be sent to the test head. The Test Head functionality will determine the tests that can be carried out.

There should be at least:

  • DC Voltage
  • AC Voltage
  • Resistance
  • Capacitance
  • TDR
  • Detect NTE / Phone
  • Phone off hook

Hover over diagram>

Line Test for copper circuits
   

Test Exchange

The TASM / TAM switches the A and B lines of the 'exchange' side forcing the two wires to be sent to the test head. The Test Head functionality will determine the tests that can be carried out.

There should be at least:

  • DC Voltage
  • AC Voltage
  • Resistance
  • Capacitance
  • TDR
  • Dial Tone

Hover over diagram>

 Test Copper Line to Exchange
   

Monitor

The line is switched as well as further relays to keep the line intact. This means the Test Head is across the line in a monitoring mode.

Hover over diagram>

 Test - Monitor a copper line
   

Test Head Checks

Two tests exist for checking the Test Head and making sure the Test Head is working okay.

  • A loop test, the Test Head is not testing the line or affecting it in any way. It should report back a loop and no other conditions.
  • A Dis test, the Test Head should report back a disconnection condition as it should find nothing.

 

Hover over diagram>

 Note: These are the main switches - Other switching modes are possible.

Test Head Checks


Further information on Copper Test Heads and metallic test access units can be found at UTEL