In order to make the AC power have a convenient power conversion function, the power transmission is usually in the form of three-phase four-wire. The three heads of the three-phase power are called the phase line, and the three tails of the three-phase power are connected together and called the neutral line. Zero line". The reason why it is called the neutral line is that no current flows through the neutral line at the moment of three-phase equilibrium, and it is directly or indirectly connected to the earth, and the voltage to the earth is also close to zero.
The ground wire is a line that reliably connects the shell of the equipment or electrical appliances to the ground, and is a good solution to prevent electric shock accidents.
Under normal circumstances, the live wire in a three-phase circuit uses red, yellow, and blue colors to represent the three live wires, and the neutral wire uses black. In a single-phase lighting circuit, generally yellow means the live wire, blue is the neutral wire, and the yellow-green alternate is the ground wire.
In some places, red is used to indicate the live wire, black to indicate the zero wire, and the green and yellow wire is the ground wire.
Can the ground wire and the neutral wire be connected together?
This connection is not safe, so it is not allowed.
The neutral wire is connected to the earth at the transformer end. Since the neutral wire from the transformer to the user has a certain resistance, the voltage between the neutral wire and the ground at the user end is often not zero. If there is no ground wire, if the electrical Fault, the neutral or live wire is connected to the metal shell of the consumer, then the voltage between the consumer and the earth is not zero, so it is unsafe. At this time, if the neutral is disconnected, it is very dangerous. The ground wire is a wire that is grounded nearby by the user. Under normal circumstances, the voltage to the earth is zero. A good ground wire is connected to the metal casing of the electrical appliance. When the electrical appliance fails, it can ensure that the voltage between the casing and the ground is zero. It plays a role of safety protection.
If the neutral wire and the ground wire are combined together as a wire, if this wire is disconnected and the switch of the electrical appliance is closed, even a normal electrical appliance will be charged with the entire shell, which is very dangerous. Therefore, when using electricity, for electrical appliances with a metal shell, in addition to the live and neutral wires, the shell must also be grounded for safety.
In actual application, I will give you three wires, one is the live wire, the other is the neutral wire, and the other is the ground wire. If the colors of the three wires are the same! How can you tell them apart?
1. The color of the phase line L (Live) must be red, yellow, and green;
The color of the zero line N (Neutral) must be black and blue;
The color of the protective earth wire PE (Protect Earth) must be yellow and green two-color wires.
2. Will you use a clamp-type ammeter to measure the live wire with an electric pen? The current of the phase wire (live wire) and the neutral wire are the same, and there is no current when the ground wire is normal.
3. There is current flowing through the neutral wire; the ground wire is used for protection, and there is no current in normal operation. There is current only when there is a short circuit and leakage. The grounding resistance is required to be small, and the equipment side is generally protected by the shell.
Measure the live wire with an electric pen, and place the test light (bulb with wire) on the live wire and one of the other two wires. If the light is on, it means the neutral wire. If the light is not on. Description is the ground wire.
The light test method is effective when the ground wire is not connected to the ground. If the ground wire is connected to the ground, the light will be on regardless of which wire is connected.
4. When there is electricity, it should not be difficult to find the live wire, but it is difficult to distinguish the neutral wire from the ground wire. Theoretically, the voltage between the live wire and the neutral wire is about 220 volts, and the voltage between the ground wire At around 190 volts. If you connect an energy-saving lamp, the brightness should be visible, and the bright is naturally the zero line, which is for reference only.
The difference between live wire and neutral wire:
The live wire and the neutral wire are both live wires. If the two-phase power supply is connected to the consumer, then there will be current flowing through the wire
It is generally felt that the live wire is electrified, because if a person touches (including some indirect contact) the live wire, part of the electric current passes through the person's body, which is like a water pipe with a tap in the middle. The neutral wire is not charged because the other end of the power supply (the neutral wire) is connected to the ground. When we touch the neutral wire on the ground, no current will be formed because there is no position difference. So there is a feeling that the neutral line is not charged. The neutral wire and the live wire are originally from the power source, and the positive direction of the current is from one end, passing through the external equipment, and entering from the other end. A loop is formed. The difference between the neutral wire and the live wire is that one of the two terminals of the power supply is connected to the ground.
The difference between neutral and ground
1. Zero line and ground line are different concepts, not the same thing.
2. The ground potential of the ground wire is zero. The nearest point of the electrical appliance used is grounded.
3. The ground potential of the neutral line is not necessarily zero. The nearest grounding point of the neutral line is at the substation or the transformer that supplies power.
4. Sometimes the neutral line will electrify people. When is it? When your electric stove is not heating up, don’t think that it’s out of electricity and won’t electrify people. It’s wrong! There may be such a possibility, away from yours. The N wire is disconnected in a place far away from the electrical appliance. If you measure it with a voltmeter, you will find that the LN wire of the electrical appliance is the voltage of the mains!
5. The ground wire will not power people, unless it is a bad situation, the designer does not understand, or the product is messed up!
6. If you have a neutral wire and a ground wire in your circuit, you will find a high withstand voltage capacitor between them.
Why can't zero ground be short-circuited?
When the zero ground is short-circuited, in case the live wire and the neutral wire are connected reversely, the entire cabinet is equivalent to being connected to the live wire, and it will be live. Why can't the live wire and the neutral wire be reversed? In the internal design of electrical appliances, the circuit of the neutral wire and the ground wire will be different, for example, a fuse will be added to the live wire. Some of Cisco's equipment can't be started if it turns around.
Fire wire is the common name for phase wire.
Mains: refers to household single-phase alternating current, with an effective value of 220V.
Three-phase power electricity: refers to industrial electricity, the voltage between phases is 380V. But the voltage between phase and ground is 220V, which is the mains supply mode.
Ground wire: In order to protect personal safety, all household appliances with metal casings must be grounded. The obvious mark of the ground wire is yellow-green (half of the wire is yellow and the other is green). It is absolutely not allowed to use the ground wire and the neutral wire together, because if the fuse of the neutral wire is broken, the housing of the household appliance will be charged with 220V mains voltage, causing personal injury. The ground wire is also not allowed to be left unused. The ground wire must be well grounded, and the grounding resistance is usually less than 4 ohms. We use a multimeter to test:
1. In the case of power failure, the resistance of the ground wire and the neutral wire should be infinite. If the resistance is 0, it means that the ground wire and the neutral wire are connected in parallel.
2. When the electrical appliance is not connected to the mains, the resistance of the ground plug of the power cord and the casing should be zero, otherwise the contact will be poor.
Neutral line: It is usually grounded at the power supply transformer, and grounded at the entrance line of the residential unit. When the neutral line is intact, there is no voltage between the neutral line and the earth.
Live wire: any phase of the three-phase power, its voltage relative to the neutral wire and the ground wire is 220V, and the voltage between any two phases is 380V. Normally, the currents flowing through the live wire and the neutral wire at the same time are equal. The wire diameters of the live wire and the neutral wire are the same.
Color requirements: the live wire is red, green, and yellow, the neutral wire is light blue, and the ground wire is a yellow-green wire.
