can someone explain the "switchloop"?


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Old 06-22-09, 02:28 PM
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can someone explain the "switchloop"?

I keep seeing this term, but don't understand the concept. can someone explain it? Or post a diagram of the wiring layout?

Thanks.
 
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Old 06-22-09, 02:59 PM
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The wire going to the switch on the left is a switch loop because both wires hot; the white one is always hot, the black one is hot when the switch is ON. It can be thought of as a single loop of wire which is broken in the middle by the switch. The loop is only a partial circuit because the neutral wire remains in the light box.

Compare that to the receptacle on the right where only the black wire is hot and the white wire is neutral. This provides a complete circuit as it has both hot and neutral wires.

The practical implication is that if you hypothetically wanted to add another receptacle, you could extend a cable from the receptacle on the right, but you could not extend a cable from the switch because of the lack of neutral wire. Switch loops cannot be extended to do anything other than switch a load.
 
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Old 06-22-09, 03:41 PM
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Excellent diagram. So in a switch loop setup, if I remove the switch and put a continuity tester to the wires, the tester shouldn't light?

trying to determine if I have power at my switch or a switch loop.

I put the tester on the wires and it lit up.
 
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Old 06-22-09, 04:03 PM
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trying to determine if I have power at my switch or a switch loop.

I put the tester on the wires and it lit up.
Invalid test. You do not check for power at a switch loop normally. It will read power through the bulb. If you remove the bulb, yes it will show infinity if the wires insulation isn't compromised.
 
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Old 06-22-09, 04:21 PM
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Switch Loop

If you have only one cable coming into the switch box, you have a switch loop. Black wire on one screw and white wire on the other screw.

Two cables would indicate one is power in and the other sends current to the light. Black wire from the power cable on one screw and black wire going to light on the other screw. Two white wires connected together.
 
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Old 06-22-09, 07:01 PM
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Appears I have a switch loop. Only one cable with only black, white, ground.

I have been attempting to add a exhaust fan/light combo. now I know why it hasn't worked the way it is laid out in the schematic.
 
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Old 06-22-09, 07:04 PM
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Originally Posted by Stumped1
Excellent diagram. So in a switch loop setup, if I remove the switch and put a continuity tester to the wires, the tester shouldn't light?

trying to determine if I have power at my switch or a switch loop.

I put the tester on the wires and it lit up.
Your tester lit up because you have completed the circuit through the element of the light bulb.

Best way to tell you have a switch loop is what Wirepuller posted or if you have a white/white taped black connected to the switch and it is not a 3 way.
 
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Old 06-22-09, 07:21 PM
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I don't know if this is an indicator, but the original switch I removed has three screws, one black, one brass/copper one side.

one copper screw on the other side.

knob & tube wiring.
 
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Old 06-22-09, 07:31 PM
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Originally Posted by Stumped1
I don't know if this is an indicator, but the original switch I removed has three screws, one black, one brass/copper one side.

one copper screw on the other side.

knob & tube wiring.
Ooo Goody! A three way switch and knob and tube. You can not actually add anything to a K&T circuit. It is against code. Also a three-way on a K&T may be wired in a dangerous and non code acceptable way.
 
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Old 06-22-09, 07:46 PM
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What would be the correct switch?
 
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Old 06-22-09, 08:21 PM
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It is the correct switch. It's the wiring that is suspect.The important thing is you can not add the fan to a K&T circuit. You need to run new wire from the breaker box.
I have been attempting to add a exhaust fan/light combo. now I know why it hasn't worked the way it is laid out in the schematic.
 
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Old 06-22-09, 08:26 PM
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I plan to put the original switch back. It just had been bugging me that I couldn't figure out the wiring.

Electrician is coming for quote to do it correctly.
 
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Old 06-23-09, 12:58 AM
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Stumped1.,

It will be the best to get the electrician deal with this stuff espcally with T&K they are very tricky to deal with it and it don't take much to screw up and what more with three way formats there is about a dozen way to get the three way to work { 90% of them do not meet the modern codes and it was written way back in late 1930's }

I allready dealt with quite few of them in both North American and European verison.

And you can not extend the T&K circuit at all.

You must run the new one to slove the issue.

Merci,Marc
 
 

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