Shorts in wiring
- Thread starter butch5
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james_mcquade
Senior Member
Re: Shorts in wiring
there is a test instrument used by the telephone industry to find the short. they told me its about 3,000.
if you know the circuit thats bad, unwire all parts, be sure to turn off all switches, unplug all devices in the receptacles and ohm out each part of that circuit. maybe someone else has a better suggestion.
there is a test instrument used by the telephone industry to find the short. they told me its about 3,000.
if you know the circuit thats bad, unwire all parts, be sure to turn off all switches, unplug all devices in the receptacles and ohm out each part of that circuit. maybe someone else has a better suggestion.
- Location
- Bremerton, Washington
Re: Shorts in wiring
Its called a TDR, and they are available for much less than 3,000. The tdr measures the lenght to the fault, it has to be calibrated for the type cable used.
Its called a TDR, and they are available for much less than 3,000. The tdr measures the lenght to the fault, it has to be calibrated for the type cable used.
Re: Shorts in wiring
TDR is overkill for the application, and not accurate enough for such a short distance. We in the telecom use a TDR to get in the ball park, then use a cable locator to mark the spot. You follow the tone with a reciever until the tone quits. They can be purchased or leased.
[ March 10, 2004, 07:52 PM: Message edited by: dereckbc ]
TDR is overkill for the application, and not accurate enough for such a short distance. We in the telecom use a TDR to get in the ball park, then use a cable locator to mark the spot. You follow the tone with a reciever until the tone quits. They can be purchased or leased.
[ March 10, 2004, 07:52 PM: Message edited by: dereckbc ]
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: Shorts in wiring
I have used underground cable locater's to find shorts between conductors many times but instead of connecting one lead to a rod placed in the ground I connect both leads to the shorted wires after disconnecting both ends of the run and trace the circuit. then leave a marker where you loose the signal. you will over run the short about 1' to 3' but just reconnect to the other end of the run and trace it again. This will place the short between the two marks. The only thing that will not allow this to work is a metal barrier like a metal race way.
I have used underground cable locater's to find shorts between conductors many times but instead of connecting one lead to a rod placed in the ground I connect both leads to the shorted wires after disconnecting both ends of the run and trace the circuit. then leave a marker where you loose the signal. you will over run the short about 1' to 3' but just reconnect to the other end of the run and trace it again. This will place the short between the two marks. The only thing that will not allow this to work is a metal barrier like a metal race way.
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
Re: Shorts in wiring
?TDR? stands for ?Time Domain Reflectometry.? It?s all about measuring the time needed for a reflected wave to make it back to the source. I studied it in college, so it is not a new technology (I graduated during the reign of Augustus Caesar). Its basic principle is similar to that of radar and sonar. The machine sends a pulsed signal down the conductor. At the end of the conductor, the wave is reflected along the wire back to the machine that created the pulse. Measure the time required for the wave to make the round trip, multiply by the speed of the wave, and you get the distance traveled by the wave. Divide by two, and you get the length of the conductor. You knew that length anyway, so the answer will be no surprise.
But if there are any ?imperfections? along the path, a part of the wave will be reflected back from the point of the imperfection. You can get the distance from the source to the point of imperfection in the same way described above. In this sense, an ?imperfection? is any point at which the resistance of the conductor changes. If you tap into the conductor and run a second circuit, the TDR will show the distance to the tap point. It will pick up a twisted and wire-capped connection in a junction box. And it will pick up the point at which a nail was driven into a conductor.
Keep in mind that all a TDR can tell you is the distance along the conductor to the point of imperfection. You will need to know how the conductor is routed through the floors, walls, and ceilings, in order to find the exact location of the point in question.
Do a google search for Time Domain Reflectometry, and you should find plenty of information.
Here is a tutorial that I found:
TDR Info
?TDR? stands for ?Time Domain Reflectometry.? It?s all about measuring the time needed for a reflected wave to make it back to the source. I studied it in college, so it is not a new technology (I graduated during the reign of Augustus Caesar). Its basic principle is similar to that of radar and sonar. The machine sends a pulsed signal down the conductor. At the end of the conductor, the wave is reflected along the wire back to the machine that created the pulse. Measure the time required for the wave to make the round trip, multiply by the speed of the wave, and you get the distance traveled by the wave. Divide by two, and you get the length of the conductor. You knew that length anyway, so the answer will be no surprise.
But if there are any ?imperfections? along the path, a part of the wave will be reflected back from the point of the imperfection. You can get the distance from the source to the point of imperfection in the same way described above. In this sense, an ?imperfection? is any point at which the resistance of the conductor changes. If you tap into the conductor and run a second circuit, the TDR will show the distance to the tap point. It will pick up a twisted and wire-capped connection in a junction box. And it will pick up the point at which a nail was driven into a conductor.
Keep in mind that all a TDR can tell you is the distance along the conductor to the point of imperfection. You will need to know how the conductor is routed through the floors, walls, and ceilings, in order to find the exact location of the point in question.
Do a google search for Time Domain Reflectometry, and you should find plenty of information.
Here is a tutorial that I found:
TDR Info
brian john
Senior Member
- Location
- Leesburg, VA
Re: Shorts in wiring
What Butch asked, I believe is? IS THERE A WAY TO TEST FOR SHORTS.
Megger, continuity testes, ohm meter
What Butch asked, I believe is? IS THERE A WAY TO TEST FOR SHORTS.
Megger, continuity testes, ohm meter
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