Practical Solutions to Static Electricity Problems
In our practical work, we often encounter problems such as computer cases being electrified, printers "leaking electricity," and speakers "shocking" people. In reality, many times the machines themselves are perfectly fine; the root cause of the "shocking" effect is that the user's home lacks a ground wire or is not providing the required power supply for the computer.
1. Theoretical Explanation
There are two main reasons for computer-related electric shocks:
1) Computer user manuals clearly state, "To ensure the normal operation of your computer, please ensure that the computer is properly grounded." The fundamental reason for an electrified computer casing is the lack of a ground wire or poor grounding in the home.
2) Because most computers sold on the market are CCC certified, CCC-certified power supplies must use EMI filtering circuits. Since this filtering circuit has capacitors connected to both the live and ground wires, if there is no ground wire installed in the home, a slight "electrification" phenomenon will appear on the surface of the casing, which is normal. Even if we test the casing with a test pen and it glows red, this static electricity will not harm the human body; only a slight "electric shock" sensation may occur upon occasional contact.
2. Comparison and Clarification
Sometimes users have questions like: Why don't other computers in the same building have leakage problems? Why does the electric heater in my home become electrified after using a computer, even though it's normally not charged?
One thing is certain: any power supply that has passed CCC certification uses an EMI filter circuit. Therefore, without a ground wire, its metal casing will definitely be "electrified." We can use two or three computers in the same environment for a comparative test. If all three machines of the same model are "electrified," it is sufficient proof that the machines have no quality problems.
As we can see from the grounding connection diagram of the computer equipment above, if any household appliances that require a ground wire are not properly grounded at the user's home's incoming power line, these appliances will connect to the refrigerator, washing machine, microwave oven, electric fan, air conditioner, computer, printer, monitor, etc., through the installed ground wire or a multi-socket outlet, forming a single, interconnected circuit. If any of these devices leaks electricity, the surfaces of all the aforementioned household appliances will become electrified.
Sometimes, even when we shut down the computer, the chassis may still be electrified. This is due to the EMI filter circuit; without a ground wire, the live wire passes through the filter capacitor, electrifying the metal chassis. Modern computers often have soft shutdown mechanisms; even after the main unit is turned off, the power supply isn't completely cut off to ensure the auxiliary power circuit continues operating. In this case, we must unplug the power cord or turn off the power strip.
Another situation occurs where the computer chassis remains electrified even after the power strip is switched off. This is because many power strips sold on the market are poorly manufactured, and their switches don't control the live wire. Incorrect wiring in the user's home, specifically a misalignment of the live and neutral wires, can also cause this. This wiring is dangerous because all household appliance switches are now controlling the neutral wire. Even if a light bulb doesn't light up or a washing machine stops spinning, the internal circuitry remains electrified, making light bulb replacement a "live inspection."
3. Emergency Measures
Since the root cause of the electrification is the lack of a ground wire, the simplest solution is to connect an electric wire directly to the casing of the appliance and connect the other end of the wire to the metal water pipe. When connecting, remove the rust-proofing layer from the water pipe and tighten the wire several times. Once the ground wire is properly connected, the casing of the appliance will not turn red when tested with a voltage tester. However, customers should be informed that this connection method is for temporary emergency use. A professional electrician must properly install a ground wire in the home to prevent accidents caused by a "leakage" from other household appliances causing the water pipe to become electrified.