How to determine the first and last ends of the motor using only a multimeter
Generally, regardless of whether the three-phase power motor is old or new, the wiring is wrapped at the beginning and end, and the wire colors are consistent and do not need to be specifically distinguished. However, there are always exceptions. As an electrician, if you encounter a wire color that is not consistent and the beginning and end are confused, it is indeed a difficult task to connect the wires. Especially for electricians who have not encountered this situation before, it is easy to be at a loss and have no clue.
Today, let's briefly talk about how to use a multimeter to find the beginning and end of the device step by step, and then mark them. This is actually one of the essential skills for electricians.
The first step is to use the resistance range of a multimeter to divide the seven wires of the motor into three groups. One group is the ground wire, which is the easiest to determine. The other two groups, regardless of the beginning or end, only need to separate the conductive wires and place them in two groups. There must be no interconnected phases in the same group. Some motors have thermal protection wires, which are usually very thin and intuitive, and can be directly distinguished from the outside.
The second step is to mark these three groups properly, as the ground wire is marked separately and there is no need to worry about it. The main task is to distinguish between the first and last ends of the lines in these two groups. Firstly, mark the three wires in one group as 1'2'3 and the other group as 4'5'6. Use the minimum current range of the multimeter to touch the ends of these two groups of wires respectively. Pay attention to ensuring that the contact is in place to prevent measurement errors caused by improper contact. After ensuring that the contact is in place, rotate the motor by hand. If there are numbers displayed on the dial and current is sensed, it means that the ends of these two groups of wires are not at the same end. Then switch the 1'4 end to become two groups, 2'3'4 and 1'5'6. Repeat the above action procedure and repeat this method until the dial does not respond when rotating the motor. When no current is sensed, it means that the ends have been successfully divided into two groups. Repeat this up to three times to successfully distinguish.
This method of distinguishing between the beginning and the end is because it involves using a probe to touch two sets of wire ends and rotating the motor. It feels like one person's hands are not enough to operate it alone. Here, I will tell you a small method that can be easily operated, which is the method shown in the picture. Use a circuit breaker to fix both the probe and the wire end. This not only ensures proper contact, but also frees up both hands to easily rotate the motor, making it much easier to operate, especially without human assistance. This is very convenient.
