Large house, many light switches, how do you determine what a switch does if "nothing happens" ?

Thread Starter

c627627

Joined May 18, 2011
46
What would be the best method to determine the purpose of a switch in a (very) large house if nothing appears to happen when you flip it ON/OFF?
 

kubeek

Joined Sep 20, 2005
5,599
Go through the wiring and see where it goes to? Call a lot of people and put them in strategic places and have them check for light/sound/heat/...?
 

jpanhalt

Joined Jan 18, 2008
7,902
It is possible that a switch controls a wall outlet, sometimes only one of the the two or more outlets per face plate.

I have never had a "very large house," but I have been known to label switches with a code for what they operate when it is not intuitively obvious.

Get a two lamps and plug each into every outlet in a room.

There will also be switches on some appliances. For example, the furnace my be controlled by a simple switch that is not labeled and looks just like a light switch. After you identify what you can, then the size of your problem will be more manageable.
 

Alec_t

Joined Sep 17, 2013
10,367
Which country are you in? (Different countries have different house wiring regulations).
Have you checked that all fuses/circuit-breakers at your incoming supply point are ok and not tripped?
 
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WBahn

Joined Mar 31, 2012
24,695
What would be the best method to determine the purpose of a switch in a (very) large house if nothing appears to happen when you flip it ON/OFF?
I've got a couple of those in my house. One we identified as going to a wall outlet (just one of the two) near the front window -- actually works great come Christmas. Another is upstairs in the main loft area and the third is in the bathroom. Never have tracked those down.

There are signal injectors you can get/make to inject a signal into the wiring and then us a small loop antenna to trace it through the walls. Not bullet proof, but can be useful. Someday that's what I'm going to try. I'm hoping this summer to tag all of the outlets and switches with which breaker they are on.
 

Uilnaydar

Joined Jan 30, 2008
118
Also, there are cases (my home for example) where it is wired for future work. For example, I have a switch at the front door that goes to a junction box leading out the front for a front yard light that is required per the HOA covenant but which nobody in the subdivision bothered putting in yet :)

This was also great for Christmas time to get the data cable out to the individual RGB controllers since -20F is not conducive to most serial communication chips on the PCs I used to control the lights.

Oh, my home also has an entire wall that had neutral/hot reversed. One of these days I might fix it. I call it the mother-in-law trap, much to my wife's disgust.
 

wayneh

Joined Sep 9, 2010
16,102
I’d start by pulling the face plate off to see if the switch is actually wired or just filling space. No wires, you’re done. I’ve got one in my kitchen for a garbage disposal that was never installed.

Then I’d plug lights into the wall receptacles. Check both sides of each receptacle - my switched outlets all are half always-on and half switched.

You could also verify there is line power at the switch. Finding which breaker it’s on might give you a clue about the function of the switch.
 

djsfantasi

Joined Apr 11, 2010
5,606
One possibility is if there are old covers where a ceiling light once existed. Open it up and measure for power, with the switch in both positions

We had this situation in our house. A ceiling light was removed, the wires capped and a cover put over the opening. In fact, my younger sister was convinced she caused the Northeast Blackout by flicking this switch.
 

dl324

Joined Mar 30, 2015
8,920
What would be the best method to determine the purpose of a switch in a (very) large house if nothing appears to happen when you flip it ON/OFF?
You may never find out. I have a couple switches in my family room that I have no idea what they switch. I have one switch that switches the power in my store room. Have no idea why they did that.
 

jpanhalt

Joined Jan 18, 2008
7,902
You may see lots of switches without an obvious purpose. One example would be a switch in a bathroom with an outside window and no fan (not required by code). My home in MN was pre-wired like that so when I installed a fan, I didn't have to pull a wire. Some people in Minnesota shower in the Winter too.

In a storeroom, it may be an outlet switch for, perhaps, a dehumidifier. And so forth.
 

spinnaker

Joined Oct 29, 2009
7,815
One possibility is if there are old covers where a ceiling light once existed. Open it up and measure for power, with the switch in both positions

We had this situation in our house. A ceiling light was removed, the wires capped and a cover put over the opening. In fact, my younger sister was convinced she caused the Northeast Blackout by flicking this switch.

In the video I posted above, Al spends the day with the neighbor tearing the house apart trying to figure out what a wall switch is for. In the closing shot, he is frustrated, frantically switching it on and off mumbling I sure wish I knew what this switch has for. Parting shot to the dog house outside. A light is being turned on and off. You hear the thoughts of the dog saying "I sure sure wish I knew what cause that light to turn on and off". :)


If the house is old, it may have gone through a number of remodels. The switch might not be connected to anything. Classic example might be a ceiling light that has been long covered over.
 

MisterBill2

Joined Jan 23, 2018
3,883
I have been through that and had clients ask me to track things down. But after a few owners in a LARGE house some functions get abandoned and some switches for outlets are jumpered so the outlet is always on. And indeed some switches are for outside plugs that are lost behind the garden. Definitely one of those tone oscillator tracers can help to see where the wires go, which is a useful start in seeing what they might do.
 

Thread Starter

c627627

Joined May 18, 2011
46
Thank you for all your advice. Can someone post why the link below
is better than this, for the purpose of finding out what a switch does, in other words wouldn't the ET250 model be better than the ET300 model?:

https://www.amazon.com/Voltage-Continuity-Klein-Tools-ET250/dp/B071Z1R8ZG
This https://www.amazon.com/Klein-Tools-ET300-Electrical-Standard/dp/B003LHJSY8 or something like it could help if the switch controls an outlet. In theory, it could be adapted for other configurations.
 
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Yaakov

Joined Jan 27, 2019
1,544
Thank you fot all your posts. can someone posts why the link below
is better than this, for the purpose of finding out what a switch does, in other words wouldn't the ET250 model be better than the ET300 model?:

https://www.amazon.com/Voltage-Continuity-Klein-Tools-ET250/dp/B071Z1R8ZG
Two different things. The tester I linked is a tone and probe. It generates a tone on the circuit of the outlet, and you can find the breaker with the probe. In the case of the switch, if it is controlling a receptacle, then the switch would sound the probe when it was turned on.

The other tester is useful, but not for that sort of test.
 

MisterBill2

Joined Jan 23, 2018
3,883
A high impedance voltmeter can be useful in determining if a wire is part of an energized system, since it can pick up several volts of capacitively coupled voltage. I hold the black lead in one hand a probe with the red lead, except when I put the black meter lead on the neutral line, or what is supposed to be the neutral line. That also is useful in finding the one wire that does not make contact inside the big wire nut with ten wires in it. THAT can be a real head-scratcher sort of problem, or the broken wire under layers of tape around and old soldered splice.
 
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