You can install smart switches without neutral, why do people still do otherwise when they can save cost? There's quite a number of smart switches that market themselves as not requiring neutral wire, no wiring hassle.
Xiaomi Aqara switches is one, Ufairy Z-Wave switch is another one, some of the Z-Wave modules such as FIBARO Dimmer 2 and Aeotec Nano Dimmer also can be installed without neutral. In fact, there are a lot of Zigbee switches on Taobao and Aliexpress that can be installed without neutral.
Why do we want to make life difficult and prefer a neutral solution when we can help customer save cost? Here's 5 reason why:
1. Protect your LED lights and drivers from damage
The reason every smart switch needs a neutral wire attached: it needs to stay powered all the time. The neutral wire does this job exactly. It allows the switch to stay powered even when the light is off. The switch uses the neutral wire to return the current back to the DB (mains) when the switch is off.
Base on the reason above, so how do switches that do not require neutral overcome this law of physic? They return the current via the switch wire, through the LED light/drivers, into the neutral in the ceiling and back to the DB (mains). Sounds viable right? This would mean that when the switch is at the off state, there is a small current flowing (sufficient to power the switch and yet not sufficient to power the lights ) running through your LED lights/drivers. Typically a Zigbee, Z-Wave switch require 1W or below so we assume 1W of current is constantly running through your lights/drivers.
Now if your lights/drivers are on/off type (non dimmable), you are constantly under powering them. Under powering an electrical appliance typical causes damage over time. Some of the low power bulbs, i.e 3W may flicker even if the switch is off because 1W of current is quite significant for a 3W light. You might even notice some of the low power lights are actually on at night when the switch is off!
2. Electronics in LED drivers degrade over time
You may experience having your switches and lights work perfectly well right after installation. However, after a while your LED drivers may degrade over time and become sensitive to that small current and start flickering.
3. Smart switch without neutral is technically a dimmer switch
This is also the reason for Z-Wave modules such as FIBARO dimmer 2 and Aeotec Nano dimmer can work without neutral. These switches/modules maintain power by cutting the current up to the minimum just like you dim a dimmer to minimum. This works better for dimmable lights/drivers as they are built to work under small current. In some cases, low power dimmable lights might still light up the bulb when the switch is off, just not as badly as a on/off light. Which brings us to the topic of bypass.
4. You may need to use a bypass
Z-Wave modules such as FIBARO dimmer 2 and Aeotec Nano dimmer, you can install a bypass at the light to increase the load of your lights so that a small current doesn't power up your lights. For Ufairy switches, they also have a bypass that synchronise with the state of the switch so that when the switch is off, the current goes thru the bypass instead of through the lights/drivers. These are inherently additional point of failures which can be forgotten after installation. If you ever change switches or brands down the road, you might wonder why there are still issues with a new switch as these bypass are made for the specific brand only. You will eventually incur cost of installing or removing the bypass.
5. It only works for wireless technologies that uses low power transmission
If you had already noticed, there is no wifi smart switches that do not require neutral. If there is, please read the technical details. This is because wifi takes higher power compared to Z-Wave and Zigbee and thus will introduce a higher current through your lights. It doesn't make technical sense to build one because it will definitely power up your lights/drivers in off state.
With all these considerations, we do not want risk having customer experience such teething issues down the road. There are so many different quality of lights and drivers in the lighting market. They degrade and respond differently to that small current thus there is no way we can guarantee a stable installation with no neutral smart switches.
So far, we are assuming all smart switches are of the same quality, but take Xiaomi Aqara non neutral switches for example, they fail so much that the Singapore distributor/reseller reduce the warranty to 7 days and stop stocking them all together.
Like we always tell our customers, going for smart switches without neutral is like weight management without regular exercise. It only works temporarily and doesn't last.
Automate Asia Team
This article is part of Series of articles to start your smart home journey, the smart Singaporean story