Looking at the input terminal of the switching power supply, it says “L” and “N” instead of “AC”. What does that mean? If you haven’t been particularly concerned about it, please read below.
Outlet 「L」 and 「N」
There is no indication on the outlet of the house or office, but there are 「L」 and 「N」. It is confusing because there are many names, but the grounded side of the outlet is called N (Neutral or Cold, GND, Minus), and the non-grounded side is called L (Live or Hot, Plus). N means neutral, and Live means that the voltage is “alive”.
If you look closely at the outlet, the length of the hole in the outlet is different on the left and right. The hole on the left is 9mm long, the hole on the right is 7mm, and the hole on the left is a little longer by about 2mm.
The longer hole on the left side is N (ground side), and the shorter hole on the right side is L (non-ground side). Since the N terminal of the outlet has the same voltage as the ground, 0V and the L terminal are 100V (± 100V, but it is 100V for easy understanding).
In rare cases, the wiring on the back of the wall of the outlet may be mistakenly connected in reverse during electrical work, and the L and N of the outlet will be reversed. In that case, you cannot tell just by looking at the outlet from the outside.
To check if the outlet is wired correctly, you can check using a device called an “electroscope driver“. The voltage detection driver has a simple mechanism that the lamp lights up when a voltage is applied to the tip. It is sold at “Kohnan” and “CAINZ” for about 1000 yen, so if you are interested, why not buy it? It’s easy to use, just insert a voltage detection screwdriver into the hole of the outlet and press the button. If the wiring is correct, you can see that the L side on the right side is lit and voltage is applied. Even if you insert it into the hole on the left side and press the button, it will not shine because it is 0V. If it is wired in reverse, the left side will shine. Please do not do the wiring work of the outlet by yourself. Only qualified personnel can do it.
Power cord for home appliances
Originally, there is a direction to plug the power cord plug into the outlet, but in the case of home appliances that we usually use, it can be used without problems even if it is plugged in the opposite way.
Some audio products and LCD TVs are specified to be plugged into an outlet. If you do not plug it into the outlet correctly, the performance will not be exhibited, so the manufacturer has specified it “on purpose”.
To distinguish, insert the white line or the line with fine letters on the AC cord so that it is on the N side (left side) ground side of the outlet. You can use it in the opposite way, but it seems that the sound quality and image quality may change. I think it’s a subtle level that ordinary people don’t understand. By plugging the power cord plug into the outlet in the correct direction, noise can easily escape from the N ground side of the outlet to the ground. It seems that noise does not enter and the sound quality becomes clear.
It’s hard to see in the picture, but there was a small letter on the power cord of the Panasonic Blu-ray recorder at home. You can insert the plug on that line into the N side (longer side) of the outlet, but the power cord can be removed from the Blu-ray recorder body, and there is no direction to insert it on that side. did. In other words, there was no direction to plug it into an outlet, and in fact, there was no mention in the instruction manual of the Blu-ray recorder about the direction to plug the power cord.
However, some devices specify the direction in which the power cord plug is inserted into the outlet. You can use it in reverse, but even if you turn off the power on the device side, the voltage will remain on the L side (100V side) just by turning off the N side (0V side) of the outlet. There may be no actual problem, but if a weak current continues to flow to the device side and this state continues for one, two to several years, there may be an electricity bill, but the life of the device is not a little affected. it might be. I think you should check the power cord at home once.
How to connect “L” and “N” of switching power supply
The safety standard stipulates that the L side of this outlet should be connected to the L terminal of the switching power supply and the N side of the outlet should be connected to the N terminal of the switching power supply. The manufacturer’s data collection is also measured by connecting in that way, so if you connect and measure in the opposite direction, the measured value of noise will be different.
There is a fuse immediately after the L terminal of the switching power supply.
If the inside of the power supply is short-circuited (short-circuit between the AC line and the ground line), the fuse immediately after the L terminal is blown to protect against electric shock. The fuse on the L side is blown because the AC line L is 100V.
The fuse will blow even if the L terminal and N terminal are connected in reverse, but the 100V on the non-grounded side (L) of the AC line remains connected to the N terminal of the power supply (100V is applied and a weak current flows). It is dangerous because it becomes.
Effect of electric shock on the human body
If a person accidentally gets an electric shock to a 100V outlet or electric wire, how much current will flow through the body? The resistance value of a person is said to be 2000Ω to 4000Ω. The resistance value changes depending on the difference in physique, whether the skin is dry or wet, or the part of the body that has been electrocuted. Roughly speaking, 2000Ω is when a small, thin person is sweating, and 4000Ω is when a large person is dry.
When calculating the current value from Ohm’s law
I (A) = V / R = 100/2000 = 0.05A = 50mA, and a current of 50mA will flow through the human body.
So how shocking is 50mA?
The following information was found on the “Workplace Safety Site” of the Ministry of Health, Labor and Welfare. According to it, 1mA makes you feel light electricity, 5mA makes you feel pain, and 50mA flows into the human body, “there is a possibility of fainting or cardiopulmonary arrest.” Cardiopulmonary arrest is when the heart is in the path of electric shock, but it is life-threatening.
I think that electric shock is more dangerous at higher voltage than current, but direct voltage is not related to electric shock. The proof is that the electrostatic voltage exceeds 3,000V, but the current value is so small that it just snaps. Whether or not you die from an electric shock depends not on the power supply voltage but on the current flowing through your body.
Although the smartphone charger is 5V, it can output a current of about 1A, so if you put the tip of the charging plug in the bath water, you may get an electric shock.
In fact, a 12-year-old Russian boy dropped his charging iphone into a bath and was electrocuted, a 16-year-old girl was electrocuted with headphones while charging his smartphone in Thailand, and a smartphone charging while taking a bath in France. A 15-year-old girl has an electric shock death accident. In the case of a 16-year-old Thai girl, her body was burned and she died instantly. It is very dangerous to operate your smartphone while charging. The charger should never be taken to the bath.
Then, isn’t there an electric shock death in the “electric bath” of the public bath? Since the electric bath runs electricity, I am “electrically shocked”. Generally, the voltage of the electric bath is 3V to 10V and the current is about 1mA to 10mA. The power supply for the electric bath is a constant current power supply so that no more current flows.
Electric shock protection standard
The EN standard, which is a unified European standard, is an international standard for electric shock. In that EN, “EN61140” divides the protection method against electric shock into three classes: class I, class II, and class III.
In reality, the type of transformer installed determines the protection class for electric shock.
Class I equipment
Protects electric shock protection only with basic insulation. If the basic insulation is damaged, the conductive part where a dangerous voltage may be applied is grounded. Switching power supplies belong to this class I equipment, and the transformer has a ground terminal that can be protected and grounded.
Class II equipment
Safety measures of “Double insulation” that protects against electric shock with basic insulation and “Supplementary insulation (thickness of insulation is secured 0.4 mm)” or “Reinforced Insulation” that has more protection performance than this Double insulation It is a device that has been given.
Class II transformers require all windings to be covered with insulation.
Class III equipment
A device that protects against electric shock with a SELV (Safty Extra-Low Voltate) circuit and does not have a dangerous voltage inside the device. There is no dangerous voltage above DC60V in the equipment.
