telephone cords with O/C conductors

[Dave Moll]

I feel almost embarassed asking this question, but I am puzzled by this one.

I have a couple of (three-core) cloth-covered telephone cords which appear visually to be fine and dandy. However, all three of the conductors on one are open-circuit and two on the other. Does anyone know any way - in the absence of x-ray equipment - of identifying where the problem lies?

[Nickthedentist]

That's odd Dave

When this type of thing occurs in most leads, the break is of course typically where the cord flexes most sharply, i.e. at the point it enters/leaves the plug, receiver, junction box or whatever.

But for it to occur in all 3 conductors is bizarre, even allowing for the fact that the actual CSA of each conductor in "tinsel wire" is very small.

Is there any evidence of damp? I wonder whether the special wrapped terminations have failed?

One method for finding breaks in transformers is by connecting a piezo generator from a lighter, boiler etc. to each end of the winding, and looking for sparks in a darkened room. Not sure whether this is of use here.

Another method would be to use a normal continuity tester fitted with tiny sharp pins, and poke through the insulation at various points to find where continuity is lost.

Good luck,
Nick.

[Dave Moll]

Originally Posted by Nickthedentist

use a normal continuity tester fitted with tiny sharp pins, and poke through the insulation at various points to find where continuity is lost.

I should have mentioned that one is overall-cloth-covered, and one is braided. I seem to remember I tried this with the one which was overall-cloth-covered, but gave up trying to find the right conductor within the sheath. I should, however, be able to use this method more successfully with the braided cord (which I have only recently acquired). If I find the breaks, I may even be able inject short lengths of wire to bridge them.

[Station X]

You could try measuring the capacitance between a pair of wires from each end of the cord. It will only be a matter of a few pFs, but most DMM having a capacitance range will go down that low.

[russell_w_b]

Originally Posted by Dave Moll

I feel almost embarassed asking this question, but I am puzzled by this one.

I have a couple of (three-core) cloth-covered telephone cords which appear visually to be fine and dandy. However, all three of the conductors on one are open-circuit and two on the other. Does anyone know any way - in the absence of x-ray equipment - of identifying where the problem lies?

I'll bet your fault is at one end of the cable, where the strain's been. It'll be necked.

The pin method sounds good to me! Buzz it out with a pin as one probe, and check the neck-ends carefully.