Smart Light Switch Basics

Figure 12 – Light Switch Locations 

But as to the devices themselves, there’s no reason to over do it while getting started. It’s nice to think about living in the Jetson’s home, but National electric code does require at least one switch controlling the light on the wall, and as a practical matter if the smart home network crashes, you want a manual override. 

While a smart home can add a wall switch for a light in a convenient place, to make up for an inconvenient place, it’s a little more complicated than meets the eye, so I do not recommend envisioning too many fundamental changes in the way we wire our homes. Light switches will still be on the walls, but perhaps we have fewer of them. Maybe the best solution is to have all the light switches in a room in one central location, as a manual override. With enough box space behind them for any kind of future lighting controller. But even if we swap out most of the light switches in the house with wifi-talking smart buttons, those smart buttons will still benefit from a hardwired power supply. That brings us back to what most would consider obvious, that one way or another we will still have hardwired power in our homes. 

Figure 13 – Traveler Circuits 

Dumb light switches, in cases where more than one switch controls a single light bulb, are like a double-side railroad line with only one train on the track. The light switch alternates from on to off, and that switches the side of the track (called traveler wires) that the electricity is on, down to the device itself. It is a literal, manual on-off switch. 

Figure 14 – Behind-the-switch Lighting Wiring

A smart switch is fundamentally different in that the power goes into the controller and then the power out to the device, skipping over the actual toggle switch on the wall. Not all switches physically regulate actual electricity, some are low voltage relays that trigger an external switch. When retrofitting an existing lighting circuit with smart switches, the power lines are intercepted by the control board, and the light switch itself is rewired as a low voltage relay. Rewiring the lighting circuit is always possible, but the installer might have to cannibalize the traveler wires to use as low voltage relay circuits and it’s not a simple process. 

Figure 15 – Different Lighting Styles 

While I have found these behind-the-box controllers to be better than the switch replacements, I have also found them too complex to install and recommend starting with a more basic switch replacement, where the controller is built into the switch itself.

We don’t have time to talk about all those nuances in two hours, but the basics is that the actual power output is routed from the controller into the device, with the switch rewired as a low voltage relay. The electricity is no longer coming from the switch itself, but the controller is in fact hardwired to the building power supply. 

Figure 16 – Qualified Persons

There is potential for safety improvements in this kind of design, but it is also work that an electrician really should be performing, if the building owner is not comfortable self-performing that kind of work. An electrician is better at doing cable management and placement than a do-it-yourselfer. The controllers are allowed to go inside the lighting junction box, but only if they take up less than 75 percent of the cross-sectional area of the box. On a finer note, most controllers have reset buttons which need to be pressed if the system or device fails. When I install these controllers, I make sure I can access that push button with a push pin of some sort, to prevent having to undo a whole bunch of wiring to access that push button on the controller.

Although the light switch replacements I’ve used have not had reset buttons of any kind, but instead require flicking the switch up and down rapidly to initiate a reset mode, and I find that method much less elegant despite the easier access. 

Another option is to have a smart light bulb, where the controller is built into the light bulb itself

Rather than a smart light switch. That’s really interesting because it doesn’t require electricians, and keeps the building wires in place. Smart light bulbs are expensive, but by the time you factor in labor they’re actually worth it. 

The  major downside to a smart light switch is that like the controller, they need to have an always on power supply to work. So if the dumb light switch kills the power to the light bulb, then lighting automations would no longer work until the analogy switch is changed. The accessible switch on the wall then becomes a hindrance – smart owners resort to taping their lights on to prevent guests from ruining the automation, which reduces the usability of the home. It’s not an easy problem to solve, although smart light bulbs often have more features such as color changing and dimming, some of which can not be delivered by a controller that controls a regular dumb light bulb. 

Figure 17 – Adding Push Buttons

I don’t really know which solution is optimal, maybe in the future all the lights in the room will be on one manual override panel, similar to a hotel conference room, with motion detectors and voice commands making up the difference. There are wireless touch plates you can get for the walls, but also, getting one manufacturer’s wireless touch plate to talk to another manufacturer’s lighting controller is not an easy task. At any rate, there are more simple solutions to implement today and we could get stuck trying to figure out the optimal wiring scheme of the future. Swapping out a few lightbulbs or wall switches and getting everything set up on voice commands is a pretty natural fit as a starting point and there are safe ways to do so without being an electrician, although other devices really do fall into the category of electrical work.

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Posted May 14, 2020 by John Cromer in category "Smart Home

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