A simple way to distinguish between zero and fire wires with a multimeter
Generally speaking, the identification of utility power in the zero line, fire, non-low-voltage test pen can not be used, with a multimeter can also distinguish between fire and zero line? The answer is yes, the method is as follows.
The multimeter range switch to AC voltage 250V or 500V gear. The black pen connected to the indoor water pipe workers wet ground, land, etc., the red pen and the power cord or power outlet hole contact, the multimeter indicates a higher voltage value for the firewire, the voltage value of the lower or zero for the zero line.
Put the multimeter gear on the AC voltage 250V gear, a meter stick connected to the wire, the other with the wall or ground contact, (if the wall or the ground is particularly dry can be made with water to make it wet point, so that the effect is more significant) multimeter pointer does not indicate that this line is zero line, the pointer deflection shows that this line is firewire. When we want to distinguish between fire and zero line and the hands of no test pen in the case, just need a multimeter to complete the test, there are three methods are described below:
The first method: if you do not have a test pen in hand only the multimeter, in the case of normal voltage, you can use the multimeter to distinguish between the fire wire and the zero line. With a multimeter pen connected to the fire line or zero line, another pen ground or walls, metal pipes, etc., if there is a voltage (generally greater than 20V), is the fire line; no voltage is the zero line.
The second method: First of all, we need to understand the principle of the test pen, electric pen by the metal rod, neon bubble, carbon resistance, and metal cap composition, neon bubble is a device that can light up, a glass ball filled with inert gas, carbon resistance voltage in 1M ohms or more, the metal cap is the human hand in contact with the parts, when the human and the metal cap in contact with the firewire, the pen, the human body, and the earth constitutes a circuit, in which the human and the earth between the existence of about 100PF. There is a capacitance of about 100PF between the earth, the circuit is so constituted.
We use a multimeter to measure, and regardless of digital or pointer multimeter, in the understanding of the general range of supply voltage, we take 220VAC voltage, for example, will be adjusted to 400VAC multimeter gear, the red pen connected to the fire line or zero line, the hand touching the black pen, the multimeter if there is a reading shows that it is the firewire; no readings show that it is the zero line.
This method will not cause any danger to the human body, the reason is that the digital multimeter internal resistance of 10M ohms, pointer table internal resistance of 20K ohms / V, if the measurement of voltage 220V, then the pointer table of the internal resistance of 20K × 220V = 4,400 ohms, absolutely safe, because the carbon resistor of the pen internal resistance is generally used 1M ohms.
