ECN Forum Forums General Topics of the Trade General Discussion Area brain teaser

Hi Bazooka,

Yep, that's the method! Did you get it Erik?

As with the example above, you can extend this one by pairing up extra wires into the daisy-chain. The group of three and the single open wire gives you the reference point that you need.

To comlete the picture, the "odd man out" is the case of 4 wires. You can solve that one thus:

On roof, link two wires, leave other two open.

In basement, identify open wires and label them as #1 and #2. Identify looped wires as #3 and #4. Tie #2 to #3.

Back on roof, ring out from looped pair to identify #2. Other open wire is #1. Remove the tie, identify #3 using #2, then last wire is #4. The only "problem" with this one is that unlike all the others you haven't confirmed continuity on all 4 wires (#1 hasn't been tested).

It's sometimes easier if you have a ground reference available, but by just using a continuity tester it's possible to correctly identify any number of wires from 3 upwards by these methods.

Sparky,
The resistance angle could be useful as well. I guess I should've specified an audible continuity tester only, no ohmmeter!

One last challenge:

How could you correctly identify just 2 conductors? You can use a continuity tester or ohmmeter, you're not allowed to use a ground reference or any other cable, but you may use one additional component.

Oh, and you can start on the roof and by the time you've finished testing in the basement, the wires should be correctly labeled at both ends. No return trip!

Start at the roof and install a diode between the two wires. Label each wire. Use the continuity tester and record the readings (1-2 and 2-1).
Make the trip to the basement and make the same checks.

Yep, that's what I had in mind!

Now, how would go about identifying just a single conductor?

Just kidding....

neat thread