Where do I connect the In-Wall Relay Module Switch?

I know people ask this sort of thing all the time, but every situation is different and when it comes to electricity I’d rather not guess.

I have 2 flourescent lights in my basement that I’d like to be able to control with SmartThings, but I’m pretty sure the owner wired the switch in a way that prevents me from using a smart switch.

I have a In-Wall Relay Module Switch which I’m assuming will solve my problem, but I have no idea where in the circuit to put it or which wires to connect to it.

All of the wires are exposed except for the vertical part of the wire above the outlet so I’d rather put in a new junction box then try to cram the device into one of the existing ones.

Here’s a diagram of how everything is connected, yellow represents the bare ground wire. I know that all 9 wires go into the light, but I didn’t open it so I’m not sure how they’re connected.

Thank you for any guidance you can provide.

Where are you seeing that because I just read through the paper manual it came with and it doesn’t say that anywhere…

Update: I didn’t by it so I never read the description on the page I linked to, but the manual doesn’t say it and nigher does the description on Amazon.

I know that the wire going to the switch doesn’t have a neutral which is why I’m not trying to use a regular smart switch.

I thought the way the outlet was wired meant that there was a neutral coming from the circuit breaker so the lack of neutral at the switch didn’t matter as long as the relay module was on the outlet side of the circuit…?

The manual only specs this for a “resistive load.” That means an incandescent light or a halogen light, and specifically does not mean LED or CFL or fluorescent (which are inductive loads).

From the manual:

Resistive Load:
800W for 110VAC

From the seller:

So @anon36505037 is correct, this particular device should not be used with your fluorescent tubes.

@Navat604 or one of the other electrical experts in the community may be able to say more.

But in general you need to look for one which is specifically spec’d for fluorescent tubes. The physics are significantly different. As one electrician explains:

Load types will differ in inrush current and arching.
While a cold resistive heating load will have a high inrush, once the temperature stabilizes it will have a relatively low interrupting current when the contactor attempts to open the load.
An inductive load will hit the contactor at both ends: There’s a high initial inrush, and there’s also a significant amount of energy that has to be dealt with when the circuit opens and the magnetic field collapses, so there’s a good sized arc when turning the load off, too.
Just did a troubleshooting call for exactly this problem on an electromagnet: They were burning through manual disconnects that were in theory rated to handle the current, but they weren’t designed to open an inductive coil that size and it was caused serious contact erosion.


Thank you for the detailed response.

It’s not that I didn’t believe @anon36505037 and I appreciate his response because after reading that I had no intention of using it anymore, I was just pointing out that the manual doesn’t explicitly say not for tube lights.

I now get that ressistive load implies that and I see that it’s explicitly stated on the sellers website, but I hadn’t visited that page before creating this post except to grab that url.

Electrical is one thing I won’t mess with unless I’m absolutely sure I know what I’m doing so it looks like I won’t be automating those lights, but one thing is still bugging me.

If those were incandescent lights and there was a neutral at the outlet, but not at the switch, could I have used this device near the outlet to control the lights?

It’s a moot point, but this post made it sound like it would work.

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You could definitely place it at the outlet to control your lights but won’t be able to use the switch. I see neutral and line both going to the left light fixture box so I would place the smart relay there because you will be able to physically turn on/off the light with the light switch.
Another option is to swap out the outlet with a smart switch, reconfigure the wiring at the first light fixture box and bring neutral and line to the old switch. Install a smart switch there without hooking up the load.

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I used this diagram found in a community post but your results may vary.

I suspect @krlaframboise was referring to a suggestion in several of the wiring threads that it is often possible to “fish up” a neutral from a nearby outlet and use that to add a neutral to a switch box that didn’t have one previously.

As I know you know, but he may not, what those posts are referring to is actually moving a physical wire. So it’s not just being close to the outlet that makes a difference, it’s finding another wire inside the wall that you can use in a different location. :sunglasses:

Most of them were talking about running a nearby neutral, but I could have sworn one recommended putting one of these where the neutral is as an alternative to running a new wire, but you wouldn’t be able to control it with the wall switch.

My thought was that the power would be cut before it made it to the first light so turning on the wall switch while the relay was off wouldn’t do anything

If the relay was on you’d be able to turn the light off at the switch, but it wouldn’t turn the relay off because they’re not connected.

I guess I’m thinking of this like a DC circuit so that concept made sense, but it sounds like I misread the other posts.

Lots of people put a micro in the light fixture if there’s a neutral there and there isn’t one at the light switch, but that’s not about a nearby neutral it’s about a neutral that you are actually going to use.

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