Quick Question - Determining Which Wire is Which (both dead wires)

Tryvidy · 04-21-2009, 06:58 PM

Hi,

I ran two 12/2 cables from my basement to the attic, now I can't figure out which one is which.

I don't have any fancy current detectors, and if I did, please suggest which type to buy for not too much money.

I need to attach a power source obviously, and connect the current at the other end with some sort of indicator (light bulb)...I tried a 9V battery and 4W lightbulb - that failed.

Please suggest a quick trick to figure out which wire is which, without hooking up to the circuit breaker panel...

Thanks again for your help!

PaliBob · 04-21-2009, 07:18 PM

Borrow or get a cheap DMM
http://search.harborfreight.com/cpis...eter&Submit=Go

*On one of the cables strip the end of the Black & White wire and twist them together.

*On the other end with the DMM set to read resistance measure each pair to determine which is shorted.

220/221 · 04-21-2009, 07:24 PM

Quote:

I tried a 9V battery and 4W lightbulb - that failed.

Was it a 9V bulb?

You need a continuity tester. I make them from a 9V battery, a 9v pizeo buzzer and alligator clips.

With tools you probably have around the house.....

Cut the male end off of an old extension cord and wire nut it on to one end of the 12/2. Plug it in and check power at the other end.

Obviously do this in a safe manner

rgsgww · 04-21-2009, 07:28 PM

I like the 12v continuity testers with led. Works great for short detecting.

220/221 · 04-21-2009, 07:40 PM

Look at the writing on the cable.

It is directional and there is a chance that one is going a different direction from the other.

PaliBob · 04-21-2009, 07:47 PM

Quote:

Originally Posted by 220/221

... and there is a chance that one is going a different direction from the other.

Good tip 50/50

Tryvidy · 04-23-2009, 02:14 AM

I ended up using a LED light from circuit city and a 9V battery, with one of end the wire being pigtailed and taking the battery and light to the other.

Strangely, the LED light burnt out rather fast. Good thing there were 2 in the package, FOR FOUR DOLLARs! wow. I should have bought a tail light or something for the same price and ripped the lights out! Maybe this is why CircuitCity went out of business in the states!

PaliBob · 04-23-2009, 06:14 AM

Quote:

Originally Posted by Tryvidy

....... I should have bought a tail light or something for the same price .........

Try, Tail Lights like other incandescent lamps are rated to operate at a specific voltage plus or minus some percent. As the voltage is lowered the lamp gets dimmer and dimmer until it goes out. As the voltage is increased the lamp just gets brighter until it burns out.

Leds operate on current. They are diodes with a threshold voltage that only work with the right polarity as you must have found out. Since they operate on current instead of voltage they need a current source commonly through a resistor, the more current the brighter the Led. The current limiter is not built into the Led. For a short time you must have had a LED that flashed like a tail light.

for more information:
http://www.theledlight.com/ledcircuits.html
.

wmldwilly · 04-23-2009, 07:36 AM

Quote:

Originally Posted by Tryvidy

I ended up using a LED light from circuit city and a 9V battery, with one of end the wire being pigtailed and taking the battery and light to the other.

Strangely, the LED light burnt out rather fast. Good thing there were 2 in the package, FOR FOUR DOLLARs! wow. I should have bought a tail light or something for the same price and ripped the lights out! Maybe this is why CircuitCity went out of business in the states!

please tell me you didn't go out and buy the LEDs and batteries and while you were on this special trip it didn't occur to you to buy a continuity tester instead?!?

jayp · 04-23-2009, 08:27 AM

I think my continuity tester was less than $10

Tryvidy · 04-23-2009, 11:11 AM

I kept asking for the continuity tester but Rona and Circuit City don't carry them, and afterwards I found one at HomeDepot. But, the LED game was fun for the price of a coffee and a good chat.

theatretch85 · 04-23-2009, 01:25 PM

Wow.

Most DMM's have a built-in continuity tester with an audible beep that can be found at nearly any hardware or electronics store. Circuit city likely carries a DMM that is realtively in-expensive and does more than just check continuity.

wmldwilly · 04-23-2009, 04:06 PM

Quote:

Originally Posted by theatretch85

Wow.

Most DMM's have a built-in continuity tester with an audible beep that can be found at nearly any hardware or electronics store. Circuit city likely carries a DMM that is realtively in-expensive and does more than just check continuity.

then again if he had called it a "digital multimeter" one of the circuit city minimum wage high school kids...um...i mean "sales associates" could have typed it into one of their register terminals and probably pointed him at one. If he'd used any term other than what they could type into a search they'd likely not know what it was, unless he was trying to buy a Wii or a DVD player.

I'd say 99% of the people working in sales at big box stores of any type have no idea what they're selling.

220/221 · 04-23-2009, 07:00 PM

Radio shack, Audible continuity tester for $5 + some electrical tape.