Wiring 3-way switch between shed and kitchen, confused by electrician
November 27, 2023 12:16 PM Subscribe
We've built a shed in our backyard and I will wire the shed electric myself. We had an electrician trench and run wire from our house to feed the shed, but I'm not sure how to wire the 3-way switch to control the shed exterior light from my kitchen given the wires he installed. Details summarized below.
Here's a basic illustration I created of the wiring https://flic.kr/p/2pigY27
Here's a photo of the wires I have within the shed https://flic.kr/p/2pibFeZ
What I'll wire in the shed:
- A dedicated 20 amp receptacle for space heater
- A couple interior 15 amp receptacles
- A couple recessed ceiling LEDs
- An exterior wall sconce controlled from shed switch and kitchen switch
- An exterior 15 amp receptacle
What the electrician ran to the shed:
- Two 12 AWG circuits
- A ground line
- Two 14 AWG traveler wires
To wire the kitchen 3-way switch and control the shed exterior light, do I use a hot and neutral from one of the "shed circuits" for both the kitchen and shed 3-way?
Here's a basic illustration I created of the wiring https://flic.kr/p/2pigY27
Here's a photo of the wires I have within the shed https://flic.kr/p/2pibFeZ
What I'll wire in the shed:
- A dedicated 20 amp receptacle for space heater
- A couple interior 15 amp receptacles
- A couple recessed ceiling LEDs
- An exterior wall sconce controlled from shed switch and kitchen switch
- An exterior 15 amp receptacle
What the electrician ran to the shed:
- Two 12 AWG circuits
- A ground line
- Two 14 AWG traveler wires
To wire the kitchen 3-way switch and control the shed exterior light, do I use a hot and neutral from one of the "shed circuits" for both the kitchen and shed 3-way?
Honestly this is complicated enough that I'd get the electrician out to wire the switch as well, if you have any doubts about how this should be done. You will absolutely need to make sure you don't inadvertently bridge two circuits as very bad things could happen if you do.
posted by Aleyn at 1:04 PM on November 27, 2023 [2 favorites]
posted by Aleyn at 1:04 PM on November 27, 2023 [2 favorites]
seconding intermod above: Use the two AWG traveler wires as the two hot legs between the 3 way switches, feed the hot from the house end of one of the 12 AWG circuits to that, and use the neutral from that same circuit* on the shed end.
* yes, all of the neutrals terminate at the same place, and you're not drawing so much on the lighting circuit that the mismatch will make a difference, but it's good practice, probably code (I am not an electrician, though I've had quite a bit of my own electrical work inspected, because good practices > code), and makes sure that if that circuit is on a Ground Fault breaker, that the lines are matched and you don't trip it.
posted by straw at 2:05 PM on November 27, 2023
* yes, all of the neutrals terminate at the same place, and you're not drawing so much on the lighting circuit that the mismatch will make a difference, but it's good practice, probably code (I am not an electrician, though I've had quite a bit of my own electrical work inspected, because good practices > code), and makes sure that if that circuit is on a Ground Fault breaker, that the lines are matched and you don't trip it.
posted by straw at 2:05 PM on November 27, 2023
Thirding asking your electrician.
This is complicated enough that just getting an answer isn't enough--you need someone who will stand by the work for your given setup. There's a definite possibility that you could get yourself in trouble here because of the subtleties.
posted by RonButNotStupid at 2:06 PM on November 27, 2023
This is complicated enough that just getting an answer isn't enough--you need someone who will stand by the work for your given setup. There's a definite possibility that you could get yourself in trouble here because of the subtleties.
posted by RonButNotStupid at 2:06 PM on November 27, 2023
Those 12 AWG circuits should be able to give you 20 Amps (and thus be equipped with 20A breaker)
Not with the 14 AWG travelers in the mix, I'm pretty sure. You'll need to use a 15A breaker for that circuit.
I agree with intermod and straw, the electrician probably intended to add a run from your subpanel to the basement junction box to supply Line and Neutral, use the two 14AWG as travelers, then attach the light to the common terminal of the 3 way in the shed. As straw notes, they'd also need to make sure the neutral to the light fixture goes back to the neutral associated with the same circuit feeding the lights, or else you'll trip any GFCI breakers.
However, I'm in Aleyn's camp here - the best thing to do would be to ask the electrician to complete the job, or at least confirm their intent. Assuming you are in the USA, you should also ask them to confirm that they are in compliance with NEC 225.30, which generally prohibits multiple branch circuits to an outbuilding, excepting some special conditions, which I can't assess if you meet.
posted by yuwtze at 2:28 PM on November 27, 2023 [2 favorites]
Not with the 14 AWG travelers in the mix, I'm pretty sure. You'll need to use a 15A breaker for that circuit.
I agree with intermod and straw, the electrician probably intended to add a run from your subpanel to the basement junction box to supply Line and Neutral, use the two 14AWG as travelers, then attach the light to the common terminal of the 3 way in the shed. As straw notes, they'd also need to make sure the neutral to the light fixture goes back to the neutral associated with the same circuit feeding the lights, or else you'll trip any GFCI breakers.
However, I'm in Aleyn's camp here - the best thing to do would be to ask the electrician to complete the job, or at least confirm their intent. Assuming you are in the USA, you should also ask them to confirm that they are in compliance with NEC 225.30, which generally prohibits multiple branch circuits to an outbuilding, excepting some special conditions, which I can't assess if you meet.
posted by yuwtze at 2:28 PM on November 27, 2023 [2 favorites]
Best answer: Neutrals have to run with their associated hot/line, just going back to the panel is insufficient and potentially dangerous both fire and shock.
Normally for a three way you need two travellers and a switch leg (total 3 wires) all contained in the same cable/conduit. In this case between house and shed. Power can be fed from either end and lights can be at either end or even the middle. There isn't a way to do this conventionally with just two wires. And depending on which code you are under you should have a neutral associated with that specific circuit in each switch box.
Faced with insufficient wire I'd feed all your lights from the shed and use caseta wireless smart switches in the shed and remotes in the house. (Assuming less than 30m/100ft to the shed which us likely considering the cable sizes). For simple paired switches you don't need a hub. They are basically fire and forget and are very reliable in my experience.
posted by Mitheral at 6:49 PM on November 27, 2023 [3 favorites]
Normally for a three way you need two travellers and a switch leg (total 3 wires) all contained in the same cable/conduit. In this case between house and shed. Power can be fed from either end and lights can be at either end or even the middle. There isn't a way to do this conventionally with just two wires. And depending on which code you are under you should have a neutral associated with that specific circuit in each switch box.
Faced with insufficient wire I'd feed all your lights from the shed and use caseta wireless smart switches in the shed and remotes in the house. (Assuming less than 30m/100ft to the shed which us likely considering the cable sizes). For simple paired switches you don't need a hub. They are basically fire and forget and are very reliable in my experience.
posted by Mitheral at 6:49 PM on November 27, 2023 [3 favorites]
IMO this conversation is a bit too deep to really help you here. I'm also not a professional electrician, but I have wired a bunch of 3 way switches (6-12, not thousands) so here's my input, and I'm going to try to dumb it down and make it really simple: Professionals feel free to correct what is wrong.
1) a 3 way switch is wired exactly the same as a normal switch with the exception of the traveler wire, which is a post on a 3way switch, I think marked as something like 'traveler' on the switch. The traveler wire is directly* between the two switches, ie: each switch has to have a traveler wire connected in the traveler post.
So that's where we are going to stop to check: Has the electrician already wired the traveler to the 3way switch inside your house? If so, you can check it there. You can also just wire the 3way switch like normal - both of them - and without the traveler, I don't recall exactly but either both switches will have to be 'on' for the lights to light or maybe the 2nd switch won't do anything - it's been a long time.
IMO: your guy wired your 3 way with a 4 wire setup as described in some of the diagrams intermod posted - so you cap off the (white generally) traveler wire at each switch and just use the colorful wire on the 'traveler' post. The only downside is you have to wire a lot more grounds. The normal line/load wires are wired exactly like a 2-way.
You'll need to check your line 1 and line 2 wires (is that what those are labeled?) in the shed to see which is carrying power from the house. The other is going to the light I guess?
IMO, unrelated: a 3 way switch is not a good idea here, unless you go to the shed in the night and return during the day. I would have wired the inside light with a 3 way switch, not the outside light, and the outside one only operable from inside the house so some shady fool can't turn it off from inside the shed. That way wiring a dusk/dawn or motion detecting light is easier.
posted by The_Vegetables at 7:18 AM on November 28, 2023
1) a 3 way switch is wired exactly the same as a normal switch with the exception of the traveler wire, which is a post on a 3way switch, I think marked as something like 'traveler' on the switch. The traveler wire is directly* between the two switches, ie: each switch has to have a traveler wire connected in the traveler post.
So that's where we are going to stop to check: Has the electrician already wired the traveler to the 3way switch inside your house? If so, you can check it there. You can also just wire the 3way switch like normal - both of them - and without the traveler, I don't recall exactly but either both switches will have to be 'on' for the lights to light or maybe the 2nd switch won't do anything - it's been a long time.
IMO: your guy wired your 3 way with a 4 wire setup as described in some of the diagrams intermod posted - so you cap off the (white generally) traveler wire at each switch and just use the colorful wire on the 'traveler' post. The only downside is you have to wire a lot more grounds. The normal line/load wires are wired exactly like a 2-way.
You'll need to check your line 1 and line 2 wires (is that what those are labeled?) in the shed to see which is carrying power from the house. The other is going to the light I guess?
IMO, unrelated: a 3 way switch is not a good idea here, unless you go to the shed in the night and return during the day. I would have wired the inside light with a 3 way switch, not the outside light, and the outside one only operable from inside the house so some shady fool can't turn it off from inside the shed. That way wiring a dusk/dawn or motion detecting light is easier.
posted by The_Vegetables at 7:18 AM on November 28, 2023
Forgot to add: you also have to purchase 3 way labeled switches. A normal 2 way switch cannot be used (I don't think).
posted by The_Vegetables at 7:41 AM on November 28, 2023
posted by The_Vegetables at 7:41 AM on November 28, 2023
I'd agree that getting the electrician back to wire it is the best option, because it is pretty complicated and it'd be tough to actually wire it to code given what you have.
Three-way switches are pretty easy to understand: there are two power wires (the traveller wires) instead of one. There is always one powered and one not powered, and the switches change between the two. So power enters a 3 way switch down the traveller you switch to. Then a three way switch on the other end connects the light to the traveller you switch to. If you want n-way switching you stick 4-way switches in the middle: they have two pairs of connections for input and output travellers and can swap which is which.
While it's nowhere near code-compliant, I'm pretty sure the intended circuit was just to grab any random lighting circuit hot wire in the kitchen and run it through a 3-way switch to the traveller wires. The kitchen switch to basement junction box run would probably be 14-2 romex with the white wire marked hot. Then the shed light is connected to them through the shed 3-way switch. It's neutral would be the outlet neutral because the heater circuit could plausibly be swapped for 240v at some point.
The problem with the code is that you're supposed to run all the wires of a circuit together (NEC 300.3(B)), and if multiple circuits go to an out building the breakers have to be grouped together and labelled (the previously mentioned NEC 225.30). Plus neutral ampacity and other stuff. It would work and it's unlikely to cause problems, but there's no way a homeowner could pass inspection with that wiring.
To be code-compliant, you'd run a third 15-amp circuit from the sub-panel to the kitchen 3-way then out to the shed through the traveller wires. If that was the intended circuit, they would have run extra wires through the underground conduit. I doubt you can pull more even if there's fill space in the conduit, but if you want to try you need a 14-gauge hot from the sub-panel to the basement, and a 14-gauge neutral from the sub-panel to the shed. Theoretically you'd also want a ground from the sub-panel to the basement, but the inspector would have to be wound pretty tight to not let you use a kitchen circuit ground for that part.
With the wires you have you can downgrade the outlet circuit to 15 amps and have a single switch in the kitchen. This still technically borrows another circuit's ground, but it's fine.
posted by netowl at 3:52 PM on November 28, 2023
Three-way switches are pretty easy to understand: there are two power wires (the traveller wires) instead of one. There is always one powered and one not powered, and the switches change between the two. So power enters a 3 way switch down the traveller you switch to. Then a three way switch on the other end connects the light to the traveller you switch to. If you want n-way switching you stick 4-way switches in the middle: they have two pairs of connections for input and output travellers and can swap which is which.
While it's nowhere near code-compliant, I'm pretty sure the intended circuit was just to grab any random lighting circuit hot wire in the kitchen and run it through a 3-way switch to the traveller wires. The kitchen switch to basement junction box run would probably be 14-2 romex with the white wire marked hot. Then the shed light is connected to them through the shed 3-way switch. It's neutral would be the outlet neutral because the heater circuit could plausibly be swapped for 240v at some point.
The problem with the code is that you're supposed to run all the wires of a circuit together (NEC 300.3(B)), and if multiple circuits go to an out building the breakers have to be grouped together and labelled (the previously mentioned NEC 225.30). Plus neutral ampacity and other stuff. It would work and it's unlikely to cause problems, but there's no way a homeowner could pass inspection with that wiring.
To be code-compliant, you'd run a third 15-amp circuit from the sub-panel to the kitchen 3-way then out to the shed through the traveller wires. If that was the intended circuit, they would have run extra wires through the underground conduit. I doubt you can pull more even if there's fill space in the conduit, but if you want to try you need a 14-gauge hot from the sub-panel to the basement, and a 14-gauge neutral from the sub-panel to the shed. Theoretically you'd also want a ground from the sub-panel to the basement, but the inspector would have to be wound pretty tight to not let you use a kitchen circuit ground for that part.
With the wires you have you can downgrade the outlet circuit to 15 amps and have a single switch in the kitchen. This still technically borrows another circuit's ground, but it's fine.
posted by netowl at 3:52 PM on November 28, 2023
Response by poster: I went with a wireless switch in the kitchen, as suggested by @unmark.
I originally forgot to mention that no electricians that I asked would wire the 3-way switch between kitchen and shed. They all tried to talk me out of it, or quoted huge prices to effectively kill that scope of the project. Running the traveler wires was the best I could get from an electrician, with the assumption I'd complete the wiring myself. The wireless switch was a no-brainer and works great.
posted by Hermanos at 4:40 PM on January 16 [3 favorites]
I originally forgot to mention that no electricians that I asked would wire the 3-way switch between kitchen and shed. They all tried to talk me out of it, or quoted huge prices to effectively kill that scope of the project. Running the traveler wires was the best I could get from an electrician, with the assumption I'd complete the wiring myself. The wireless switch was a no-brainer and works great.
posted by Hermanos at 4:40 PM on January 16 [3 favorites]
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How long is the wiring run, from the house breaker panel to the shed junction box? Those 12 AWG circuits should be able to give you 20 Amps (and thus be equipped with 20A breaker) if and only if the wiring run isn't too long. Otherwise they'd need to be downgraded to 15 Amps, due to resistive losses on that long run. If the electrician already equipped them with 20A breakers then he already evaluated this and it's fine. I just wouldn't run any heaters or big motors on those 15A receptacles.
posted by intermod at 12:59 PM on November 27, 2023 [1 favorite]