Understanding downlight and dimming switch wiring


  #1  
Old 10-06-22, 12:54 PM
F
Member
Thread Starter
Join Date: May 2011
Location: USA
Posts: 51
Received 0 Likes on 0 Posts
Understanding downlight and dimming switch wiring

I have some 5-8-year-old recessed/downlight fixtures and I'm having a hard time understanding how they are wired. There are a total of 4 fixtures wired to a single dimming switch; the lamps are dimmable. The part I'm having issues with is understanding how they're wired, my understanding is that with a more traditional switch, you have the line wire controlled by the switch, you connect the line wire in one of the terminals and get it out to the load from the other terminal, simple enough, you turn the switch Off and the wire going to the load no longer have current. In this case, the dimming switch has a white wire in one of the terminals and a back wire on the other terminal, the funny thing is that no matter what I do, turn On/Off the switch, the current on the wires doesn't change, the black wire is always live and the white wire never becomes live. I went and tested the terminals directly on two of the fixtures and the black wire is always live and the white wire never becomes enegized.

My question is, how are the fixtures turning On and Off if the current doesn't really change? Again, I was expecting the same behavior you get when using a traditional switch where you cut the circuit by turning Off the switch and the fixture becomes unenergized.

FYI - The fixtures seem to be wired in series since I see conduit going from one fixture to the other and ending on the fourth fixture.

Any help will be greatly appreciated.

Thanks!

 
  #2  
Old 10-06-22, 03:55 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Jersey
Posts: 70,969
Received 3,171 Likes on 2,847 Posts
A little confusing.

What is there for wiring at the dimmer ?
Is it just one two wire cable with white and black on the dimmer ?

If that is correct.... you have a switch loop.
That means you will probably find the switch line and power in one of the light fixtures.
 
The following users liked this post:
  #3  
Old 10-06-22, 06:25 PM
F
Member
Thread Starter
Join Date: May 2011
Location: USA
Posts: 51
Received 0 Likes on 0 Posts
Yes, it's just one white and one black wire going to the dimmer switch. Here is what I'm observing.
- When the fixtures are turned off, the white wire has current and the black one has no current.
- When the fixtures are turned on, non of the wires have current, not even the white wire. In other words, the black wire never becomes energized and the white wire is only live when the fixtures are turned off.

I hope it makes sense.

That means you will probably find the switch line and power in one of the light fixtures.
Would you mind elaborating more on this, does this mean that there will be a switch in one of the fixtures?

Thanks a lot for your help!
 
  #4  
Old 10-06-22, 06:55 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Jersey
Posts: 70,969
Received 3,171 Likes on 2,847 Posts
This shows one method. The switch and power go to one light.
Then each consecutive light is added on in parallel.



OR.... you could have a splice box with power, the switch and a cable to the first light.
The junction box would need to be in an accessible location........
OR.... all four fixtures connect directly to the junction box.

I'm illustrating the way the circuit should be properly wired.
Makes perfect sense.... by your description.... the neutral was switched and that is not correct.

 
The following users liked this post:
  #5  
Old 10-07-22, 06:15 AM
F
Member
Thread Starter
Join Date: May 2011
Location: USA
Posts: 51
Received 0 Likes on 0 Posts
Thanks a lot for following alone and for the clear diagram. What seems different from the diagram you posted and what I'm seeing is the fact that the black wire never becomes hot in my configuration and it looks like in your diagram the black wire will be hot when the switch is on, right?

- Again, what I see is that when the fixtures are Off, the white wire on the switch has current and the black one doesn't. And when the fixtures are On, none of the wires have power, this is the main part I'm confused with.

Again, thanks a lot for your help.
 
  #6  
Old 10-07-22, 02:57 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Jersey
Posts: 70,969
Received 3,171 Likes on 2,847 Posts
Ok.... you see how a correct switch loop should be wired. Hot is always switched.
This diagram shows you what you have.
When the switch is off.... hot travels thru the bulb filament and shows up on one side of the switch.
The other side of the switch is dead as it's neutral.
When the switch is closed... the wire that was hot is connected to neutral.
Now... nothing shows hot. This is a switched neutral.
 
The following users liked this post:
  #7  
Old 10-07-22, 04:27 PM
F
Member
Thread Starter
Join Date: May 2011
Location: USA
Posts: 51
Received 0 Likes on 0 Posts
Ah, so it's switching the neutral instead of the hot, got it, makes sense now. For some reason, this method seems a little unsafe. Is there any reason why one would choose one over the other? Or when it makes sense to go with a switched neutral?

As always, thanks a lot for your help!
 
  #8  
Old 10-07-22, 04:33 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Jersey
Posts: 70,969
Received 3,171 Likes on 2,847 Posts
It would appear that it was done by someone that didn't know what they were doing.
 
The following users liked this post:
  #9  
Old 10-07-22, 08:16 PM
F
Member
Thread Starter
Join Date: May 2011
Location: USA
Posts: 51
Received 0 Likes on 0 Posts
Ah ok, I just thought it was somewhat standard. Thank you very much for your help.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: