# Power detection technology / Power detection

## Detection Technology

### 3 points of experience in the use of megohmmeter

time：2021/1/6   source：华天电力  reading：777 time

1. Method of measuring leakage with megohmmeter

Use the on-off gear of the megohmmeter to measure the ground and the circuit part to be measured. If the meter shows a resistance value, it is judged not to be insulated.

But in fact, if you want to measure the leakage current, you should use a megohmmeter and shake the meter, because the voltage at both ends of the test pen is very low when measuring the megohmmeter, generally not more than 9v, and it cannot penetrate the gap and leakage, while the megohmmeter can reach more than 1000v , Insert the megohmmeter connector into the corresponding terminal for measuring alternating current, then use a pen to measure the neutral or ground wire, and the other pen to measure the place where you suspect leakage, and see the megohm indicator. If it is 0, say so here No leakage, no voltage! If it is 220 or other voltage indications exceeding 36V, all are leaking, indicating that this is not safe!

Measure the insulation resistance with a megger resistance file of 200M, first determine which line is leaking or which two lines are short-circuited.

Methods as below:

Measure the insulation resistance of the live wire and the neutral wire, measure the insulation resistance of the live wire to the ground wire, and measure the insulation resistance of the neutral wire to the ground wire. If a short circuit, the insulation resistance is basically zero.

Know which line is leaking, and use the segmented search method to gradually narrow the fault range.

Or use the elimination method to divide the circuit into a section-by-section power-on test.

2. How does the megohmmeter distinguish the zero line and the live line

Generally speaking, to identify the neutral wire and the live wire in the mains, you must use a low-voltage test pencil. Can a megohmmeter distinguish the live wire and the neutral wire?

The answer is yes, the method is as follows:

Set the range switch of the megohmmeter to 250V or 500V, the black meter pen is connected to the indoor plumber's wet ground, ground, etc., and the red meter pen is in contact with the power cord or power socket hole, and the voltage indicated by the megohmmeter is higher. For the live wire, the voltage value is low or zero is the neutral wire.

3. The method of measuring the zero line of fire with a digital megohmmeter

With a megohmmeter, you can easily measure the zero line and live wire of your home, as long as you use the AC voltage range of a digital megohmmeter, clamp-type megohmmeter, and pointer mechanical megohmmeter. AC voltage range (should all megohmmeters have this function, the range is from 200mV to 750V, generally select 200V range, some clamp meters do not have 200V range, you can choose a larger range.

The pointer megohmmeter should be smaller, you can choose 10 V 100V) and then insert the red and black test leads into the V/COM (usually measure the 220V voltage of household appliances) and wind the black test lead wire in the left hand for 2-3 turns ( (See the picture) Of course, the more the better, pay attention: at this time, the metal needle of the black test pen must not touch your hand to prevent electric shock and then you can test. Take the red test pen in your right hand to test the socket or the zero live wire separately, and you record 2 measurements As a result, there must be a large voltage and a small voltage between them. The large voltage measured is the live wire, and the small voltage value is of course the neutral wire. If the ground wire must have no smaller voltage or even no voltage (depending on you Is the ground wire of the home connected?) The difference between the measured voltage of the neutral wire and the live wire is clear at a glance.

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