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Advice on how to deal with surprise we found (changing light fixture)

Advice on how to deal with surprise we found (changing light fixture)

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  #1  
Old 07-24-19, 12:33 AM
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Advice on how to deal with surprise we found (changing light fixture)

I offered to help a friend update a lighting fixture in his house... should be simple enough.

Pulled down the old one to find a wiring surprise I was not ready to deal with! See attached picture, but basically, there are 2 NM 2 conductor cables runinning into the junction box (so far so good), but the hot (black wires) from the 2 NM cables were just wired together and then the old light fixture was wired to the the neutral lines (one wire from from fixture to one NM neutral and the second wire from fixture to the other NM neutral).

So, basically, IF the rest of the wiring is using standard color coding, etc. this is basically wiring lights in serial, not parallel as normal. In standard EE terms, this would mean you get the sum of the resistance in the circuit rather than the parallel calculation of resistance. So, clearly not standard and not great...

However, WHAT TO DO.

1. I could just put the new fixture back in the same way. Not changing anything, but this is not standard wiring as I understand it.

2. I could do the normal thing and do black to black and white to white (in parallel). However, I don't know ANYTHING else about the rest of the wiring in the house and would be worried about my "fix" having issues with the rest of the existing wiring.

I really don't want to mess with anything else in the house, but I want to do things correctly and want my friends house to be safe.

I do have a multimeter if there are some tests that I could do to confirm or deny what other issues may be in play on this circuit.

Appreciate any and all help in dealing with this surprise. What would you do if you found this situation?

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Last edited by PJmax; 07-24-19 at 07:33 PM. Reason: enlarged picture
  #2  
Old 07-24-19, 04:43 AM
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Hi, how is the switch wired? what color conductors?
Geo
 
  #3  
Old 07-24-19, 04:44 AM
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See nothing wrong with the wiring in the pic. The 120 vac power comes into the junction box on 1 b/w cable. The white goes to one terminal of the light. The black wire of the same cable is wire nutted to the black wire of the second cable. I assume the second cable goes to a switch. The white wire of the second cable provides the switched 120 vac to the other terminal on the light. Other lights can be connected in parallel with this light and controlled by the one switch. Hope this helps.

Mod Note: the switch loop should supply power to the switch on the white and return on the black to the fixture. The picture shows an incorrectly wired switch loop.
 

Last edited by pcboss; 07-24-19 at 04:49 PM.
  #4  
Old 07-24-19, 06:44 AM
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That is wiring for a normal switch loop; one of the white wires is used as a switched hot. By modern code that wire should be remarked with black or red tape, but that was not required in a building of the age pictured. The new fixture can be installed exactly as the old one is connected at the orange wire nuts.
 
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Old 07-24-19, 08:26 AM
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Thanks for the responses.

I totally get it now. The light fixture is at the "end" of a circuit (the last outlet) and wants to be switched. So, right, run an extra NM out to the switch to get power to it and then bring it back, switched, to the junction box.

Now a days, the white would have been marked red or black, and I think that would have kicked my brain enough to understand.

To confirm this is the case, I will go look at the switch the fixture is wired to and here I should see 1 NM coming in and the black switched to the white (I would have also been surprised at that, but likely realized this is what is going on).

Again, thank you all for your help, I totally get it now (and will confirm this is the situation).

Cheers!
 
  #6  
Old 07-24-19, 08:33 AM
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It will work just fine if connected the same as the old one.
However it is not wired to code. The white wire should sending power to the switch and the black should be bringing switched power. That is so you don't end with exactly what you have, two white wires connecting to the fixture and you don't which one is the hot.
 
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Old 07-24-19, 04:47 PM
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It is simply a miswired switch loop. It is not a change to serial wiring. The mnemonic to remember a correctly wired switch loop is down on the white, back on the black. This prevents the double whites at the fixture.
 
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Old 07-24-19, 06:39 PM
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pcboss, thanks for the update on electrical code. I still say the circuit is wired correctly (electrically) but not color coded correctly. When a small appliance with a 2 pin plug (lamp cord, no ground) is plugged into an outlet both ways, is the circuit wired correctly both ways or just one way? Appliance works both ways.
 
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Old 07-24-19, 07:38 PM
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No.... technically the circuit is not wired correctly. Yes it works but if you have two white wires..... how do you know which is the switched hot and the neutral ? The same thing at a receptacle. You want the switched hot to be on the small slot. Many plug in devices aren't polarity particular but some are and have a large and small prong on the plug.
 
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Old 07-26-19, 06:33 AM
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I am not a licensed electrician but I hope they don't teach them to only rely on insulation color to determine which wire is hot, especially when both wires are same color.
 
  #11  
Old 07-26-19, 10:41 AM
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Hi, itís also important to know which is the neutral so as to connect the neutral to the screw shell of the fixture.
Geo
 
 

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