How to determine the beginning and end of the motor using only a multimeter
Generally, three-phase power motors, whether they are new or old, are wired separately from the beginning to the end, and the wire colors are in the same phase, so there is no need to distinguish them. However, there are always exceptions. As an electrician, if you encounter a machine with inconsistent wire colors , the beginning and end are also confusing, and it is indeed a troublesome task to connect the wires. Especially for electricians who have never encountered such a situation, it is easy to be overwhelmed and have no clue.
Today, let's briefly talk about how to use a multimeter to find out the beginning and end step by step in this situation, and then set the mark. This is actually one of the essential skills for an electrician.
The first step is to use the resistance setting of the multimeter to divide the seven wires of the motor into three groups. One group is the ground wire. This is the easiest to determine. The other two groups do not matter the beginning or the end. Just put the conductive ones into two groups separately. There must be no interconnected phases inside. Some motors have thermal protection wires. Generally, the wires are obviously very thin, which is very intuitive and can be directly distinguished from the outside.
The second step is to mark these three groups. Because the ground wire is marked separately, don't worry about it. The main task is to distinguish the head end or the tail end of the wire ends in these two groups. First, mark the three wires in one group as 1'2'3 and the other group as 4'5'6. Use the minimum current setting of the multimeter to touch the two wire ends respectively. Be sure to make sure the contact is in place to prevent the measurement from being caused by insufficient contact. To ensure the error, after the contact is in place, turn the motor by hand. If there are numbers displayed on the dial and current is induced, it means that the two sets of wire ends are not at the same end. (https://www.diangongwugwu.com/Exclusive original copyright ) Then change the 1'4 end to two groups of 2'3'4 and 1'5'6. Repeat the above action procedure, use this method and so on, until the dial does not respond when the motor is turned, and no induction is detected. When the current is flowing, it means that the head and tail ends have been successfully distinguished into two. If you repeat this at most three times, the distinction can be successful.
This method of distinguishing the head and tail requires touching the two sets of wire ends with a test pen and turning the motor. It feels like one person's hands are not enough to operate it. Here I will tell you a small method that can be easily operated, as shown in the picture. The method is to use a circuit breaker to fix the watch needle and wire end. This not only ensures the contact is in place, but also frees your hands. You can free your hands to easily turn the motor, which makes the operation much easier, especially if there is no one to assist. , which is very convenient.
In addition, this method is universal for both digital and pointer tables. As long as you master the method and follow it step by step, it is not difficult to determine the beginning and end. Find an analog multimeter (a digital meter can also be used, but the numbers jump out a lot, so you have to pay attention to the amount of change). First use the resistance setting to find out the three sets of windings. This is easy, just measure the continuity directly. There is definitely resistance. It is one group, and the infinite one is from another group.
Then use the AC milliamp level to identify the first and last ends of a winding. The essence is to confirm the same end. According to the motor design, connect the wires according to the figure below. If the head and tail connections are correct, there will be some residual magnetism when rotating. When rotating, it will emit a little electricity. At this time, the three phases are balanced, so the multimeter is equivalent to the neutral line, which should not be There is current flowing through it.
