[Old House Upgraded to Smart Home] Can a single live wire smart switch be installed in an old house without a neutral wire (neutral wire)? Integrated estimation of power micro-flicker, capacitor fast charging and hydropower weak current

The pain point of renovating old houses into smart homes: the "neutral wire" cannot be found when opening the switch box

With the popularity of smart home systems such as HomeKit, Aqara, Tuya and Google Home in Taiwan, many homeowners in Shuangbei hope to replace the traditional light switches in their homes with "smart touch/micro switches" when renovating their old homes or doing DIY upgrades to achieve remote control of lights with mobile phones, turn off lights by voice, and link automated scenes. However, when everyone happily bought the smart switch and took apart the traditional switch box on the wall, they were instantly dumbfounded: There were only two wires of the same color in the switch box (live wire in and live wire out), and there was no "neutral wire (Neutral Wire, commonly known as C wire)" necessary for the operation of the smart switch chip! Can a smart switch be installed here? Will it cause the LED bulb to flicker slightly? How to correctly plan water and electricity lines?

Physical Principle: Why does the traditional switch box have no neutral wire?

In the traditional building water and electricity configuration, the function of the switch is simply to "break the live wire (L) in series". The power starts from the distribution box, the live wire passes through the wall switch box, and then extends to the ceiling lamp. Finally, the other end of the lamp is connected back to the neutral wire (N) to form a closed loop. Therefore, when the plumber pulls the wire, he will only pull the live wire into the switch box, and there is no need for a neutral wire inside the switch box.

However, modern "smart switches" contain Wi-Fi, Zigbee or Thread wireless communication chips and relays inside, and these chips themselves require 24-hour uninterrupted power supply. If there is no neutral wire in the switch box, the smart switch cannot form its own power supply circuit.

Comparison of two major technical solutions: single live wire switch vs. complementary neutral wire (zero fire two-wire version)

Solution 1: Use "No-Neutral Smart Switch"

The single live switch uses a very small standby current (microampere level) to maintain the operation of the internal chip through a weak series connection of light bulbs.

• Advantages: Suitable for sites where old houses do not require wall-drilling or heavy-duty wiring, eliminating the need for water and electricity wiring expenses.
• Fatal flaw (micro-flickering will-o'-the-wisp): Because a weak current continues to pass through the bulb, when low-power LED projection lamps or low-quality LED bulbs are used at home, the bulb will often glow weakly or "ghosting/flickering" every few seconds after the lights are turned off. A "safety anti-flicker capacitor (Capacitor)" must be connected across both ends of the ceiling lamp to absorb the microcurrent, and the total power limit of the lamp that can be loaded by a single live wire switch is low.

Solution 2: During water and electricity renovation, the whole house switch box "supplementally pulls the neutral wire (zero-fire two-wire version)" - (highly recommended by experts)

If you are preparing to renovate an old house or reconnect the entire house in the greater Taipei area, please be sure to ask the plumber to install an extra green or blue neutral wire (N wire) in each wall switch box!

• Advantages:The smart switch uses an independent zero live wire for power supply. The power supply is extremely stable, the response speed is fast and it never drops out. It is perfectly compatible with any power and type of LED bulbs, water drop lights, and strip lights, completely saying goodbye to the micro-flickering problem of light bulbs. Moreover, the price of the zero live wire smart switch is usually 20% to 30% cheaper than the single live wire version.
• Wage costs: When re-pulling water and electricity in the whole house, an extra neutral wire can be threaded through the pipe to the switch box. The increased material and wage costs are extremely low.

Shuangbei old house upgrade smart lighting project CapEx abacus

For owner-occupiers who want to build a high-tech luxury home, or real estate flip investors who want to package a medieval house as a high-premium "smart minimalist house", the budget for smart switch line planning is as follows:

Conclusion: One more line at the front end will save ten years of detours in the future

The key to upgrading an old house to a smart home is not to purchase expensive smart devices, but to pre-plan the front-end water and electricity infrastructure projects. When renovating and replacing electrical wires in an old Shuangbei house, the plumbers and electrical technicians were insisted on equipping each switch box with a neutral wire (neutral wire), which could lay the most stable IoT electromechanical architecture for the whole house at a very low cost. Say goodbye to the micro-flicker nightmare of a single live switch, and make every step of control in smart homes precise and smooth.

The Ministry of Economic Affairs' latest "Regulations on Consumer Electrical Equipment Installation" and the key points of electricity safety in old houses

Due to the popularity of high-power household appliances (such as air fryers, microwave ovens, dishwashers, instantaneous electric water heaters, and IH furnaces) in recent years, the Energy Administration of the Ministry of Economic Affairs has revised the "Regulations on Consumer Electrical Equipment Installation" many times to strictly require the diversion and protection mechanisms of residential electricity circuits. Statistics show that more than 30% of building fires in Taiwan are caused by electrical factors, among which "old wire insulation deteriorates and short circuits", "socket contacts are oxidized and loose, poor contact" and "non-fuse switch (NFB) overloaded and failed to trip" are the three main fatal causes.

Old apartments in Shuangbei that are more than 30 years old have a total original designed power capacity of only 30A to 40A, and several rooms often share the same 1.6mm or 2.0mm circuit. In the modern standard safety configuration, kitchen electrical cabinets, bathroom equipment, and air-conditioning and heating machines must all be equipped with 5.5mm² dedicated circuits (single circuit and single socket). It is recommended that the main switch box be upgraded to a busbar (Busbar) integrated distribution board, and the total amperage is increased to 75A or 100A (a qualified electrical appliance contractor needs to be entrusted to Taipower to review the additional power capacity).

Residential electricity self-test and regular inspection checklist

• Appearance and temperature of the socket: Touch the outer cover of the commonly used socket lightly with the back of your hand. If it feels lukewarm or if you find that the plastic socket is yellowed and charred, or the plug is loose and shaking after being plugged in, it means that the internal copper plate clamping force is exhausted or the contact resistance is too high, and you should immediately cut off the power and replace it.
• Regular testing of leakage circuit breakers (ELCB): For leakage circuit breakers in humid places such as balconies, bathrooms, and kitchen sinks, regulations require that the "TEST button" on the switch be pressed once every 1 to 3 months to confirm that it can automatically trip and cut off the power supply instantly.
• Serial connection and overloading of extension cords are strictly prohibited: Extension cords should be purchased with 2.0mm thick wire diameter products that have CNS certification and automatic overload power-off protection. Do not share the same extension cord with high energy-consuming appliances to ensure zero hidden danger to life and property at home.