A Copper Line Test is performed to check the conditions on a line (pair of wires) between the service provider and the customer. Before the introduction of digital services like ADSL, DSL, VDSL and Voip the performance of the line was not so important. A good connection is now key to keeping the customer happy by providing a fast, problem free broadband service. It is likely that a customer receiving a poor service will look to move to another service provider.

The test may be carried out for a number of reasons.

  •       The customer has reported a fault.
  •       The line is being checked for suitability of Broadband (pre-qualification).
  •       Night routining - pre-emptive fault checking.
  •       Due to a disaster such as flooding, strong gales etc.
  •       Change of service provider (Local Loop Unbundling).

Service Affecting Faults.

Any of the conditions shown below are likely to have an effect on DSL performance. It is possible to have a fault on the line which completely disrupts the voice (PSTN) but has absolutely no effect on DSL (Broadband). Faults found during testing are normally fixed before looking into a DSL reported fault.

Communication Providers (CP) offering Broadband over another operators line (Local Loop Unbundling LLU) will check if your voice service is having any problems before they accept a fault.

Typical Service Provision.

Typical Telephone Line from exchange to customer


Possible Metallic Checks

Distance: TDR

An acurate distance measurement from the central office (exchange) to the customers premises. This can be used to detect where the fault is along the circuit, it is especially helpful when used with a database that holds distances of cabinets or distribution points. It is also used to check if the line qualifies for Broadband or other services.

There are a number of testers available that can automate the hard part of testing diagnostics. If the fault is identified quickly and accurately the operating costs can be reduced. Sending an engineer to the right place immediately reduces time and preventing un-necessary truck rolls which save money. Check the product pages to find a suitable Tester that meets all you requirements.

AC Voltage.

There should be no ac voltage on the line. People doing DIY extensions have been known to put 240V mains onto the circuit and items such as modems can fail and put weird voltages like 85V out on the pair

AC voltage

DC Voltage.

Any dc voltage coming back from the line side is wrong and is likely to be from faulty equipment at the customers premises.

A DC voltage of 50V would be expected on the exchange side, a feature may include listening in for dial tone.

DC Voltage

Earth A leg / B leg.

Earth on one of the legs is quite common, caused by your phone line pair making physical contact with another pair or simply to earth. Mainly caused by water pennetration, damp or badly made connections.

Earth Faults on Telephone circuits

Loop or Short Circuit.

A "Loop" or short circuit is often caused by water penetration or damp getting into distribution boxes. Bad connections in junction boxes where exposed wires are touching or connecting with other wires in the cable.

Short Circuit or Loop


The overall resistance in the circuit can affect the quality service and also indicate a fault. Resistance between the A and B legs of the pair can be affected by penetrating damp, water impairment, loose connections, distance etc. Some of these faults maybe intermittent and occur more when the weather is bad.



The measured capacitance is relative to the cable type and cable length. Most Telecom companies will have a standard value per kilometre of cable. Capacitance is affected by the number of joints along the cable length, the number of splitters and filters in the customers premises and customer connected devices such as modems.


Further detailed information can be found at