Tracing Cables with Tone and Probe

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How to identify an individual cable from a bundle.

What is the test set used for?
Sending tones down cables to identify distant ends where they coincide in a common location such as a connection cabinet or data cabinet where all cables converge.
Consider a CCTV system, where there are several cameras at various locations about the same site, all the cables go back to a common single location where the CCTV recorded and Player are located. How does one tell which cable is which if the cables have not been labeled?
A convenient and quick way would be to use a tone and probe kit although this is snot the ONLY way to work out and organize the cables, it is a 'convenient and time effective way to do the job.

Tone Generator (oscillator)
This has a switch with three positions, “off / tone / cont, and two or three leads and a LED indicator.
Two leads will have crocodile clips and a third lead will often have a RJ11 telephone plug or RJ45 Network plug and sometimes an adapter for a BT telephone jack.
There is always an LED indicator which is used in continuity testing, and often indicates other functions.Like tel-line present or ringing The unit is powered by a battery, usually a PP3

Switch positions
Off position is where you would 'park' the switch when the oscillator is not in use, preserving the battery. (This position is selected when testing for tip and ring of telephone line condition)
Tone Position is where the switch would be set to send a tone down the cable being traced.
Usually the switch lever position is closer to the cables from the tone unit
Cont' Position. Short for continuity, can be used to test continuity and by shorting across the black and red croc clips a LED light is lit to indicate continuity. B

Things to know before we start.
Testing the function. 'Cont'
Lets start with the simplest function continuity. Flip the switch to the 'cont' position and short both crocclips together. The LED light will illuminate (Green usually) and seperating the clips extinguishes the LED indicator.
e.g. when testing a pair on a CAT5 cable stripping a pair (note the colour) at the remote end and twist the conductors together.You can then test the samepair at the other end by connecting a croc clip to each. Obviously this is a very inconvenient and time-consuming way to identify cables but it will have it's uses with intelligent application.

Testing the function, 'Tone'
This is the most useful function of the set and uses both tone generator and probe in combination with each other. Flip the switch to tone and ensure the croc clips are separate. Taking the tone probe in your hand press the trigger and hold the probe close to (not touching) the crocodile clips. You should hear either a solid or warble tone depending on the particular model of tone generator . You have confirmed that the function is operational. Now holding the probe in one hand try to short the crocodile clips red and black together while listening to the tone probe picking up the tone. *The volume of the tone should significantly reduce or become inaudible. Seperating the croc clips again,you should once again hear the tone.
*We can use this to our advantage later at the common end where we want to identify an individual cable from a bundle.

Testing the function
Telephone Line Condition.
There is only one way to test this function and thats by using it.
With the switch in the off position and a suitable RJ11 to (local) telecom connector adapter plugged into the telephone line a red indication light should appear indicating “ a line present”
Now the fun bit. Call the number of the line and see the LED flicker Green with the ringtone.
Sometimes, these colours are reversed. You will discover the setting on your own tester by opening the Line outlet the first time you use this function thereafter you will know which way round it is with that particular unit, make a note and keep in the carry case as an 'aide mémoire'

Tone cable Identify.
The Tone Generator has a Black and a Red lead. Positive and negative you might think, but really they are send and return. You could use either cable to send but if you earthed the unit on a common earth you would be sending the tone down the earth point and therefore would be potentially sending the tone all over the building. Of course this would make tracing almost impossible therefore consider these leads as Pos & Neg. Also when using a butt set, use the pos/Neg orientation to power the line.

Two Stage identify.
This technique is used most successfully when identifying 'category' cables i.e. twisted pairs. At the far-end of the cable, first connect the tone generator to a single pair and send the tone down that pair. I always start with the Blue pair, this is just my own preference and it could be any other pair.
Stage 1 (Pre Test)
Test the tone function before setting out to trace the cable at the common end (patch panel).
Stage 1 (identify & trace)
Having confirmed the tone function, attach to your selected cable and colour pair,positive to one conductor and negative to the other. Now go to the common end and take hold of a bundle of cables to be identified and eliminate one bundle then split the remaining bundle into two bundles and eliminate one of the resulting bundles. Repeat this until just one cable remains. The tone should be loudest for this one cable and stripping the ened off, separate the four pairs and compare the volume between the pairs, the pair you chose should be louder than any other pair (and should be in my case the blue pair)
Stage 2
Finally strip the ends off the pair where you heard the loudest tone (blue? ) , and while amplifying the tone, short the pair together. If the tone drastically reduces in volume or disappears altogether, then you have confirmed that you have successfully identified your cable to the exclusion of all others. (See, I told you we could use this to our advantage later).

Very often, if you are working in a noisy environment, or in a busy office where there is noise or the tone might disturb the staff, you can use a headset or earpiece to concentrate the tone volume at your ear. Various tone sets use different styles of connector. Proskit uses a 3.5mm mono jack, Greenlee use a 3.5mm jack or a crocodile clips, BT probes uses a BT style plug, and Tempo/ Progressive Electronics use crocodile clips only.
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