Check networks with a cable tester

We consider using Ethernet cables as the fastest and most reliable form of home networking, but it can still have problems if there are breaks in the cable. Using a cable tester can help to track down cables that are broken or cheaper ones that may be slowing the network down.

For this workshop we're using the RJ11/RJ45 cable tester from Maplin. It only costs £10 and it can test both network (RJ45) and telephone (RJ11) cables.

The cable tester is made in two halves so you can test a cable that has already been installed and can't easily be removed. It's also powered by a standard 9V battery.

Plug both ends of the cable in, there is one of each kind of socket on the remote and the main unit. Hold down the power button for a couple of seconds and the cable tester will turn on.

The lights will come on in sequence as the different wires inside the cable are tested in turn.

A missing light either shows that the wire is not connected (some cables are cheaper because they include fewer wires) or that there is a break somewhere.

Another thing to look for is if the lights are not in sequence. Some RJ45 cables are wired differently and known as crossover cables. Most routers should be able to cope with these kinds of cables, but it could the cause of connection problems. Try using a normal cable in case this solves the problem.

There is also a manual mode if you find the lights move to quickly. Hold down the button again for a couple of seconds and the unit will bleep. Press the button briefly to cycle through the different wire.