best way to trace electric cables

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  #1  
Old 10-17-06, 08:32 AM
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best way to trace electric cables

What's the best way to trace electric cables to figure out where all the cables go, what order lights/outlets are connected, etc? I have an older home (1950's) and some parts of the wiring look really hairy to me (a number outlet/lightswitches have 3 cables going in / coming out of the box). I'd really like to document the cable runs so I can get a nice overall view of how everything is setup in my house.

Ideas?

Thanks,
Jesse
 
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  #2  
Old 10-17-06, 09:28 AM
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The first step is to make a map of the house with each switch, light and receptacle on it. Next, turn one circuit off at the fuse or breaker and go around the house with a lamp or voltage tester and identify which outlets are on the circuit. Mark the circuit number on your map next to each outlet. Repeat for each circuit in the house.

After the circuits are mapped out, you can make a pretty good guess as to the path of the cables. Circuit originate at the main panel and travel from outlet to outlet usually in a straightforward way so as to not waste cable. Obviously if you have attic and/or basement access, you can physically track part of the cable route.

The actual cable routes are much less important than the circuit map. The circuit map is an invaluable tool when you need to work on the electrical system later.

> 3 cables going in / coming out

This is very common. You usually have one cable feeding power in, one going to a switch or light fixture, and one feeding power out to the next outlet. The only way to identify which one is which is trial and error. I don't recommend doing this unless you are trying to fix a specific problem; if it ain't broke, don't fix it.
 
  #3  
Old 10-17-06, 09:35 AM
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The actual path of the electric cables is not extremely important, and may not be completely possible.

What you can determine, and what you should determine, is what is on each and every circuit in the house.

Some day when you have plenty of time and someone to help you, turn off all the circuit breakers in the panel or remove all the fuses.

Then, one at a time turn on each breaker or replace each fuse. When the breaker is on, completely tour the house and determine which lights or appliances have power and which recetpacles have power. This is easier accomplished by turning on radios and lights before you turn all the breakers off. Don't forget receptacles outside, int eh basement or garage, and built in's such as the furnace, water heater, etc.

After determnining what is on a particular circuit breaker, turn the breaker back off.

When you have gone through all the breakers, you should have complete listing which includes each and every light, appliance and receptacle in the house.

If you really want to go further, you can figure out the path of the cables. This can be done partly by guesswork and partly by brute force.

You can sometimes follow the wires in the basement. You can make educated guesses, as runs typically are shorter rather than longer. You can disconnect wires in boxes and verify the runs. Or you can buy a tools to attempt to follow the electrical signal in the walls. I say attempt because this is not foolproof.

Understand that unless you plan to try to split a circuit, knowing the actual path doesn't gain you much. It is useful if a connection fails, but even then you can usually figure it out, as long as you know what is on each circuit.
 
  #4  
Old 10-17-06, 09:37 AM
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Originally Posted by ibpooks
The actual cable routes are much less important than the circuit map. The circuit map is an invaluable tool when you need to work on the electrical system later.
the main reason i want to know the actual route is in some places where I want to install a GFI outlet that will have also another outlet protected by it


> 3 cables going in / coming out

Originally Posted by ipbooks
This is very common. You usually have one cable feeding power in, one going to a switch or light fixture, and one feeding power out to the next outlet. The only way to identify which one is which is trial and error. I don't recommend doing this unless you are trying to fix a specific problem; if it ain't broke, don't fix it.
fortunately, the messiest one was the easiest to figure out: bathroom with heat lamp, vent and light .. it was a bit tricky to figure out which way the electricity flowed because of the difference b/n the old switch and the new one i was replacing it ... but some careful thinking about it made it all become clear

thanks for the info!
 
  #5  
Old 10-17-06, 09:42 AM
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Originally Posted by racraft
The actual path of the electric cables is not extremely important, and may not be completely possible.
really, the main thing i need to know is the order in which a few outlets are connected to the breaker box for GFI (as mentioned in a post i just finished) ... educated guesses on the actual route of the cable is good enough


Originally Posted by racraft
What you can determine, and what you should determine, is what is on each and every circuit in the house.
as i'm replacing all the ivory outlets/switches with white ones, i'm trying to remember to jot it all down ... mostly just so i don't have to go through lots of trial and error when turning off circuits ...


Originally Posted by racraft
This is easier accomplished by turning on radios and lights before you turn all the breakers off.
heh, we have a carbon monoxide alarm that chirps when the electricity goes on/off ... it's loud enough i can hear it from downstairs, so when working on outlets that comes in extremely handy!


Originally Posted by racraft
Don't forget receptacles outside, int eh basement or garage, and built in's such as the furnace, water heater, etc.
ahh, good point ... i'm not sure i even know where all the outlets are outside and i've lived in this house since May of last year :P

thanks!
 
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