Using 3 way switch as a power source selector

[sling]

I’m sure the answer is out there, but it’s buried in all the normal 3-way switch wiring results. I’m wondering if I can use a 3-way switch to select two different power sources for a light.
Specifically, I would like to take power from a garage door opener light socket, and also from the regular lighting power of the garage. Wire each source of power to the traveler terminals. Then connect the common to another light.
That way the light cycles on/off with the garage door opener in one switch position and is just on in the other position.
Is this legal? Advisable? Is there a better way? Thoughts? Don’t worry about the load limit of the opener socket, it would only be powering a 13w LED.

 

[exranger06]

No, not code compliant, and it can be very dangerous. Just get a separate light fixture for the garage door opener.

EDIT: I've thought about it some more, and it could be done safely IF the door opener is on the same circuit as the other power source. Not only that, but you'd probably have to use an inlet like this: https://www.amazon.com/Leviton-5278-CWP-Straight-Flanged-Receptacle/dp/B003ATXIBG
and run an extension cord from the socket on the opener to the inlet. Run Romex or other approved building wire from the inlet to the switch.

Even then, I'm not sure it would be code compliant, since it's a very unorthodox way of hooking up a light. It would be safe practically, however.

EDIT #2: I've thought about it even more and realized that the way I suggested is not code compliant either, since there is nothing preventing someone from plugging something else into the inlet, including things on a different circuit. So, no I don't think this can be done unless you use transformers, low-voltage signal wiring and relays and make this way too complicated.
I still recommend just using a separate fixture for the opener.

 

[wyliesdiesels]

If both hot wires are from the same circuit in the panel then it may work.

If theyre from opposite legs in the panel, then you would have 240v potential and I wouldn't do that.

 

[Lightning rod]

If the concern is that residential 3 way switches ( otherwise known as single pole, double throw) are not rated for 240 volts ( two legs) , then the attched switch can be used
https://www.homedepot.com/p/Gardner-Bender-20-Amp-Single-Pole-Toggle-Switch-1-Pack-GSW-13/100122325
And switch plate
https://store.leviton.com/collectio...-stainless-steel-84013-40?variant=32121282947
You can also drill a blank plate
Even though what the op is trying to do is not typical of the average homeowner,
It can be done safely with the proper rated switch.

These switches are used by the millions in industrial control applications.
Power comes “IN” on the outside terminals and the center terminal goes to the lamp that is being controlled

 

[sberry]

You could wire up light controls with switches. Making it part of 1 circuit would be best.

 

[MikeF2316]

I've often thought of doing this to my furnace so I can connect it to a UPS when/if the power goes off for a long period.

Fortunately, the longest power outage I've ever endured was 25 hours...

 

[sling]

Thanks for all the feedback!
Keeping it on the same circuit would be easy. Although I’m not sure how I could end up with 240 either way.
A few more details, so we’re all thinking about the same thing;
Currently the detached garage has a 70A sub panel. All the lighting is on one 15A breaker. I have a 2ft overhang outside my garage door. Under there I have a damp location rated LED fixture that lights up my driveway. This light is controlled by a regular switch by the side entry door. All inspected and up to code.
I would like that light to cycle with my garage door opener lights in addition to being manually controlled. Chamberlain sells a light controller interface for $40. But that seems expensive and cumbersome for what I want to do. I don’t need WiFi control and all that.
Tapping the hot on the opener lights and routing through a three way switch would power the light with that leg and the neutral that’s common to everything in the sub panel. Conversely, powering with the existing hot at the switch already would supply the outside light with that leg and the same neutral.
So yeah, if the opener is on circuit using the other leg, there’s 240 potential in the box, but no way of selecting both 120s at the same time. If that’s what’s meant.

 

[sling]

Also, the 3 way switch just seemed the most stealthy and elegant way to do it. The issues you guys bring up is exactly why I posted.
If anybody can think of another way that less creative (sketchy), lay it on me!

 

[wyliesdiesels]

I've often thought of doing this to my furnace so I can connect it to a UPS when/if the power goes off for a long period.

Fortunately, the longest power outage I've ever endured was 25 hours...

Not a good idea.

Unless you have a really big UPS, it wont be able to handle the inrush current of the motor.

I once plugged a small fan into a decent sized UPS. When the power went out, it tripped the UPS and the battery failed.

 

[exranger06]

Thanks for all the feedback!
Keeping it on the same circuit would be easy. Although I’m not sure how I could end up with 240 either way.
A few more details, so we’re all thinking about the same thing;
Currently the detached garage has a 70A sub panel. All the lighting is on one 15A breaker. I have a 2ft overhang outside my garage door. Under there I have a damp location rated LED fixture that lights up my driveway. This light is controlled by a regular switch by the side entry door. All inspected and up to code.
I would like that light to cycle with my garage door opener lights in addition to being manually controlled. Chamberlain sells a light controller interface for $40. But that seems expensive and cumbersome for what I want to do. I don’t need WiFi control and all that.
Tapping the hot on the opener lights and routing through a three way switch would power the light with that leg and the neutral that’s common to everything in the sub panel. Conversely, powering with the existing hot at the switch already would supply the outside light with that leg and the same neutral.
So yeah, if the opener is on circuit using the other leg, there’s 240 potential in the box, but no way of selecting both 120s at the same time. If that’s what’s meant.

The neutral is not common to every circuit in the panel. You have individual branch circuits in the panel that each have their own neutral. You cannot use the same neutral wire for more than one circuit unless it's a multi-wire branch circuit. This is why I said it could maybe be done ONLY if the opener is on the same circuit as the other power source. Plus, if the outlet that the opener is plugged into is GFCI protected, it will trip immediately as soon as the opener tries to turn the light on, if you use the neutral from the other power source's circuit.

 

[sweetk30]

why not just hit the light on button for the door opener ?

i used a screw in bulb to outlet adapter and a 4ft led shop light from sam's club on mine . and if i need light longer i just hit the light button on the genie door opener . it stays on as long as i dont turn it off .

 

[jlv03]

Currently the detached garage has a 70A sub panel. All the lighting is on one 15A breaker. I have a 2ft overhang outside my garage door. Under there I have a damp location rated LED fixture that lights up my driveway. This light is controlled by a regular switch by the side entry door. All inspected and up to code.
I would like that light to cycle with my garage door opener lights in addition to being manually controlled. Chamberlain sells a light controller interface for $40. But that seems expensive and cumbersome for what I want to do. I don’t need WiFi control and all that.
Tapping the hot on the opener lights and routing through a three way switch would power the light with that leg and the neutral that’s common to everything in the sub panel. Conversely, powering with the existing hot at the switch already would supply the outside light with that leg and the same neutral.
So yeah, if the opener is on circuit using the other leg, there’s 240 potential in the box, but no way of selecting both 120s at the same time. If that’s what’s meant.

$40 seems dirt cheap once you factor in everything you will need to do what you want - new 3 way switch, NM-B running from the opener to the switch location, light bulb sock adapter to get the opener light power, the inlet box detailed above, etc. Keep in mind the Chamberlain/Liftmaster switches run off the garage door opener frequency - no WiFi needed or required (although could be used to set schedules and some other automation).

240VAC might be better in this case as you would lessen the risk of overloading the neutral. If you pull the light and the garage door opener (GDO) off the same legs of 120VAC in the panel, you may overload the neutral. Say your lighting circuit is already running at 13A on a #14 wire before turning on the outside light. Now you have the switch set to GDO - the light pulls 3A off the GDO circuit, but is returning the current via the already loaded light neutral, for a total of 16A! Granted this is highly unlikely - your outside light wouldn't be a tipping point of tripping the breaker. Key would be to prevent plugging in or adding anything additional while the switch is on the GDO circuit.

Speaking of WiFi - I have my Liftmaster GDO connected to the Internet and to my Wink home automation hub. I have a set of Zwave light switches in the garage that are also connected to the Wink system. When the GDO opens the door the outside lights turn on to 100% brilliance. The lights stay on until the garage door closes, then dim a bit. After 10 minutes the lights turn off altogether. I can turn the lights off/on manually via the switches, and, if I leave them on an automated sweep occurs at 10:01PM and 12:01PM to turn them off.

 

[sling]

As for load, the entire garage is lit by LED. If all eight lights @ 11w each upstairs and all four lights downstairs @ 15w each and the two driveway lights @ 13w each are all on simultaneously, the draw is 174 watts / 1.45A on a 15A circuit.

There’s no cost for me to do my hack. Conduit is already in place and I have a spare switch and a few feet of red 14ga thhn laying around. Even so, I don’t mind the $40 Chamberlain light control. It’s just another box to mount, WiFi control to set up, and low voltage wiring to run for it. It’s like buying two iPhones just to talk to my wife in the next room. I was just looking for something cleaner.

Also, I don’t want to beat up this discussion on a common neutral, but I feel like I’m missing something there. All the circuits in this sub panel have the hot from the breaker and the neutral from a neutral bar running across the top of the panel. So every neutral comes from a lug on that bar. How can each circuit have its own neutral, when they are literally bolted together at one spot? A YouTube link or instructional site would be appreciated. Because I thought I had a pretty decent grasp of what was going on until this came up.

 

[yatg]

Maybe on a MWBC, but your garage probably isn't wired that way. Then years after you move some electrician is going to open the box and say "WTF is this?"

At my last house, I used the garage door opener lamp socket to trigger a relay. That relay turned on the overhead lights on a separate circuit when the garage door was opened. Those same lights could also be turned on via a wall switch.

 

[sling]

I have a bunch of relays and components I could make a little low voltage circuit out of. So that would be a another fun/free way to accomplish the operation I want. Not as simple or elegant, but would eliminate the unconventional use of the three way switch.

 

[jlv03]

Even so, I don’t mind the $40 Chamberlain light control. It’s just another box to mount, WiFi control to set up, and low voltage wiring to run for it. It’s like buying two iPhones just to talk to my wife in the next room. I was just looking for something cleaner.

Just to be sure we are talking the same thing, is this what you are referencing for $40?

https://www.chamberlain.com/smart-light-switch/p/WSLCEV-P1

It just replaces your light switch. No extra wiring, it just programs the same as a remote. Garage opens, lights go on. Garage door closes, lights eventually turn off.

 

[rsanter]

You can do this by using a relay.
Change the current switch to a three way.
Install a relay wired like the second switch would be.
Run a feed line from the opener to trip the relay

While you can do that, easier way is to install a separate light fixture connected to the opener

 

[exranger06]

As for load, the entire garage is lit by LED. If all eight lights @ 11w each upstairs and all four lights downstairs @ 15w each and the two driveway lights @ 13w each are all on simultaneously, the draw is 174 watts / 1.45A on a 15A circuit.

There’s no cost for me to do my hack. Conduit is already in place and I have a spare switch and a few feet of red 14ga thhn laying around. Even so, I don’t mind the $40 Chamberlain light control. It’s just another box to mount, WiFi control to set up, and low voltage wiring to run for it. It’s like buying two iPhones just to talk to my wife in the next room. I was just looking for something cleaner.

Also, I don’t want to beat up this discussion on a common neutral, but I feel like I’m missing something there. All the circuits in this sub panel have the hot from the breaker and the neutral from a neutral bar running across the top of the panel. So every neutral comes from a lug on that bar. How can each circuit have its own neutral, when they are literally bolted together at one spot? A YouTube link or instructional site would be appreciated. Because I thought I had a pretty decent grasp of what was going on until this came up.

It doesn't matter that all of the neutrals are bolted to the same bar. Each neutral wire connected to the bar can only carry so much current. For a moment, forget about the panel and the neutral bar. Think of a receptacle outlet on your wall. If you remove the cover plate and look at the wiring connected to the receptacle, you'll see 3 wires: a hot leg, a neutral, and a ground. Let's say this receptacle is on a 15 amp circuit, and the wiring is 14 gauge wire. The hot leg AND the neutral are both 14 gauge. There's a reason for that. If you plug in an appliance, and that appliance draws 12 amps, you would have 12 amps flowing through the hot leg AND that SAME 12 amps would ALSO be flowing through the neutral.

Now if you connect a neutral from some other circuit onto that 14 gauge neutral, and that other circuit is drawing 7 amps, you would have a total of 19 amps flowing through that neutral wire back to the neutral bar. (12 amps + 7 amps = 19 amps). A 14 gauge wire can only handle 15 amps, not 19 amps. What happens when too much current goes through a wire? Electrical fire! And the breaker will NOT turn off the power in that situation, because the neutral wire connects directly to the neutral bar, not the breaker. So the breaker has no idea that the neutral is being overloaded. One breaker is seeing 12 amps going through the hot leg, and it's assuming that only 12 amps is going through the neutral as well, so everything should be fine, and it keeps the power on. The other breaker see 7 amps going through the hot leg, so it assumes it has 7 amps going through it's OWN neutral wire, so again, it keeps the power on. Neither breaker knows that some dingus has wired the 2 neutrals together and there's one 14 gauge wire trying to carry up to 30 amps of current.

The breakers in the panel are all "bolted to the same bar" too. It doesn't mean you can tie hot legs from two different circuits together. So why do you think it's ok to do it with the neutral?

 

[theoldwizard1]

I’m wondering if I can use a 3-way switch to select two different power sources for a light.

You are barking up the wrong tree !

You want a DPDT (double pole, double throw, Leviton 1286) switch. it can switch both the hot and the neutral. Grounds can be combined.

 

[pioneer1]

It doesn't matter that all of the neutrals are bolted to the same bar. Each neutral wire connected to the bar can only carry so much current. For a moment, forget about the panel and the neutral bar. Think of a receptacle outlet on your wall. If you remove the cover plate and look at the wiring connected to the receptacle, you'll see 3 wires: a hot leg, a neutral, and a ground. Let's say this receptacle is on a 15 amp circuit, and the wiring is 14 gauge wire. The hot leg AND the neutral are both 14 gauge. There's a reason for that. If you plug in an appliance, and that appliance draws 12 amps, you would have 12 amps flowing through the hot leg AND that SAME 12 amps would ALSO be flowing through the neutral.

Now if you connect a neutral from some other circuit onto that 14 gauge neutral, and that other circuit is drawing 7 amps, you would have a total of 19 amps flowing through that neutral wire back to the neutral bar. (12 amps + 7 amps = 19 amps). A 14 gauge wire can only handle 15 amps, not 19 amps. What happens when too much current goes through a wire? Electrical fire! And the breaker will NOT turn off the power in that situation, because the neutral wire connects directly to the neutral bar, not the breaker. So the breaker has no idea that the neutral is being overloaded. One breaker is seeing 12 amps going through the hot leg, and it's assuming that only 12 amps is going through the neutral as well, so everything should be fine, and it keeps the power on. The other breaker see 7 amps going through the hot leg, so it assumes it has 7 amps going through it's OWN neutral wire, so again, it keeps the power on. Neither breaker knows that some dingus has wired the 2 neutrals together and there's one 14 gauge wire trying to carry up to 30 amps of current.

The breakers in the panel are all "bolted to the same bar" too. It doesn't mean you can tie hot legs from two different circuits together. So why do you think it's ok to do it with the neutral?

Just following along here, I appreciate you being more detail in your explanation. But help clarify this for me.
If you flip the breaker and it turns off the Wall switch AND turns off the outlet the GDO is plugged into, does this mean they are on the same circuit with the same ground?

 

[sling]

.. Each neutral wire connected to the bar can only carry so much current.

Now if you connect a neutral from some other circuit onto that 14 gauge neutral, and that other circuit is drawing 7 amps, you would have a total of 19 amps flowing through that neutral wire back to the neutral bar. (12 amps + 7 amps = 19 amps). A 14 gauge wire can only handle 15 amps, not 19 amps.

The breakers in the panel are all "bolted to the same bar" too. It doesn't mean you can tie hot legs from two different circuits together. So why do you think it's ok to do it with the neutral?

Thank you for taking the time to completely explain that. I appreciate it because these circuits are just logically grouped not sharing any kind of heavy load. Adding 11w to a circuit that is only At 10% seemed like no big deal. But if the opener were on the circuit with the outlets and I had a table saw and the dust vacuum and who knows what all running, I now understand the issue you’re pointing out of using the hot from one circuit and the neutral from another.
To be clear, I whole reason I posted this was it seemed I was missing something important about wiring it like this. The only reason I thought using two different hot legs to alternatively power the light was “okay”, and I was never sure about it, was that each hot leg is breaker protected and the neutral from the light is extremely lightly loaded. I get that someone, or even me, might come along later and decide to use some of that excess capacity.

 

[sling]

Just to be sure we are talking the same thing, is this what you are referencing for $40?

https://www.chamberlain.com/smart-light-switch/p/WSLCEV-P1

It just replaces your light switch. No extra wiring, it just programs the same as a remote. Garage opens, lights go on. Garage door closes, lights eventually turn off.

Your link is +$10 because it has a motion sensor, but yeah, that thing. I did overestimate the work. The current switch for that light is in a 3 gang box with other switches. So I was thinking to relocate along side and such. I realize that actually no low voltage wire running back to the opener in this case.
I know their device will work, it just seems like technological overkill. All the functionality is already there. I was just hoping there was a trick way to combine them so the opener operated like one end of a three way switch. Apparently, the only way to do it is with 40-50 dollars worth of WiFi enabled electronics.

 

[MikeF2316]

Just following along here, I appreciate you being more detail in your explanation. But help clarify this for me.
If you flip the breaker and it turns off the Wall switch AND turns off the outlet the GDO is plugged into, does this mean they are on the same circuit with the same ground?

Nothing is ever 100% certain, but, yes they will be on the same circuit.

(And the correct term in house wiring for the return path is neutral, not ground, but they would share the same ground too.)