Use of electric wire detector
(1) tips for judging ac and dc: the electrical circuit tester determines ac and dc, the ac is bright and the dc is dark, the ac neon tube is bright and the dc neon tube is bright.
Description: first of all, let the reader know that it is necessary to test on the confirmed charged body before using the low-voltage electroscope pen.The electroscope pen shall not be used until it is confirmed that it is normal.When judging alternating current and dc current, it is better to compare them between "two current", which is obvious.When measuring alternating current, both ends of the neon tube shine at the same time. When measuring direct current, only one end of the neon tube is extremely bright.
(2) determine the positive and negative terminals of dc: the pen determines the positive and negative terminals. Observe the neon tube carefully.
Description: the front end of neon tube refers to one end of the power tester pen point of the electroscope pen. The back end of neon tube refers to one end of the hand grip.When testing, attention should be paid to: the power voltage is 110V and above;If a person is insulated from the earth, one hand touches either pole of the power supply, and the other hand holds the measuring pen.If the back end of the neon tube is bright, the measured power supply is positive, according to the principle of dc one-way flow and electron flow from negative to positive.
(3) the key to determine whether the dc power is grounded or not, and the difference between positive and negative grounding is: dc coefficient of the substation, touch of the pen is not bright;If the light is close to the pen tip, there is a ground fault at the positive pole.If the light is close to the finger, the ground fault is at the negative pole.
Description: the dc coefficient of power plant and substation, is of insulation, people standing on the ground, with the test pen to touch the positive or negative, neon is should not shine, if light, is that dc system grounding phenomenon;If the light is at the end near the pen point, it is grounded.If the light is near the end of the finger, it is negatively grounded.
(4) the formula for judging homogeneity and heterogeneity: judge the same difference between two lines, hold a pen in both hands, insulate both feet and ground, touch one important line in each stroke, and look at a pen with the eyes.
Note: in this test, remember to insulate both feet and ground.Because most of our country is 380/220 v power supply, and neutral directly grounding transformer widely adopted, so do the test, the human body and the earth must be between insulation, avoid a circuit, so as to avoid mistakes;In the test, the two strokes are the same as the two strokes, so you can only see one.
(5) the formula for determining the phase line grounding fault of the 380/220v three-phase power supply line is as follows: star connection three-phase line, the electric pen touches two bright, the remaining one is weak in brightness, and the phase wire has been grounded;If it's almost dark, the metal grounding is out of order.
Description: power transformer secondary side is generally take into Y, in three-phase three-wire system of neutral point grounding system, the test pen touch the three phase line, two root, slightly brighter than usual, but on the other less brightness, said this brightness weak phase line grounding phenomenon, but also not too serious;If two of them are bright and the remaining one is barely visible, there is a metal grounding fault in the phase line.
Attention of electrical testing tools
(1) before using the electricity detector pen, first check whether there is safety resistance in the test pen, and then visually check whether the test pen is damaged, whether there is damp or water inflow. It can only be used after passing the test.
(principle: there is resistance test pencil, the luminous body - neon, the key lies in neon, after resistance step-down, to the end of the voltage to neon, form a high potential, your hand contact with the metal end of the pencil end, now you are the earth, have two pieces of thin metal wire in neon, get very close, but I don't even, natural is filling in the neon neon, have suitable potential difference can glow discharge is produced.Breakdown neon if the voltage is too big, can instantly when the neon insurance role, will not have much damage to you, low voltage will be dangerous, because traditional pencil, is neon pencil, in more than 100 v or so bright, the effect can not, don't water the other pencil, or else you will know the feeling of electric shock.)
(2) when using the test pen, you should not touch the metal probe at the front of the test pen with your hand, which will lead to electric shock.
(3) using a test pencil, must use hand to touch the metal part of the end of a test pencil, otherwise, because of the charged body, test pencil, the human body and the earth did not form a loop, neon bulb does not shine in the test pencil, wrong result, don't think charged body is charged, it is very dangerous.
(neon glow voltage is 70 v, the series resistor of 500 k, the test voltage 220 v, the biggest electric current flows through the human body: I = (220-70), present 500 = 0.3 mA and the human body by below 30 mA of current are considered safe.)
(4) before measuring whether the electrical equipment is charged, it is necessary to find a known power source to test whether the neon bubble of the electric pen can glow normally and glow normally before it can be used.
(5) when testing charged bodies in bright light, special attention should be paid to whether neon bubbles are actually emitting light (or not), and if necessary, another hand should be used to block out the light carefully.Don't make a mistake by judging neon light to be non-luminous and electricity to be non-electric.