Testing Continuity of a Group Of Wires - Cables
Another simple continuity tester design, probably better than the above two, is shown alongside. The circuit can be specifically useful for testing long cables consisting of more than a single core wire or having a group of wires.
The circuit is again very simple, a couple of NPN transistors are configured as a Darlington pair emitter follower circuit to achieve high sensitivity. An LED is used as indicator at the collector of the transistor which lights up when continuity between the ends of the conductor under test is detected.
The circuit may be built over a small general purpose PCB and housed inside an appropriate enclosure along with a 3 volt cell for powering the circuit. The output leads will also need to be terminated appropriately.
The testing of continuity of a group of wires may be done individually using the above circuit in the following manner:
As shown in the figure, consider a cable consisting of four core wires having colors as blue, navy blue, green and brown.
Each wire may be checked individually for continuity, for example beginning with the blue wire the testing may be done by holding one of its stripped ends with your finger and touching the other end of the wire to the base terminal of the circuit (the positive terminal being held with the other hand.)
If the wire is OK, the LED will instantly light up indicating continuity. No response from the LED will indicate a possible break in the continuity of the wire.
Similarly, the other strands may also be verified.