How to use only one multimeter to determine the beginning and end of the motor
Generally, regardless of whether the three-phase power motor is new or old, the wiring is wrapped at the beginning and the end, and the wire color is the same as the same phase, so there is no need to distinguish it, but there are always exceptions. , The beginning and the end are also chaotic, and it is indeed a troublesome thing to connect the wires, especially for electricians who have never encountered such a situation, 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 out the first and last ends step by step in such a 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 gear of the multimeter to divide the seven wires of the motor into three groups. One group is the ground wire, which is the easiest to determine. There must be no connected phases inside, some motors have thermal protection wires, these wires are generally very thin, very intuitive, and can be directly distinguished from the outside.
The second step is to mark these three groups, because the ground wires are marked separately, so don’t worry about it, the main task is how to distinguish the end of the wires in these two groups from the beginning or the end. First, 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 two groups of wire ends respectively. Be careful to make sure the contact is in place to prevent the measurement caused by improper contact. Error, after ensuring that the contact is in place, turn the motor by hand. If there are numbers displayed on the dial and current is sensed, it means that the two sets of wire ends are not at the same end. Then change the 1'4 end to 2'3'4 And 1'5'6 groups, after repeating the above action procedures, use this method and so on, until the dial does not respond when the motor is turned, and when no current is sensed, it means that the head and tail have been successfully divided into two, so repeat at most Three times, you can distinguish success.
This method of distinguishing the beginning and the end, because the test pen is used to touch the two sets of wire ends, and the motor needs to be rotated, it feels that one person does not have enough hands to operate it. Here I will tell you a small method, which can be operated very easily, which is shown in the picture. The method is to use a circuit breaker to fix the needle and the end of the wire, which not only ensures that the contact is in place, but also frees the hands, so that the motor can be easily rotated with the hands free, and the operation is much easier, especially when there is no assistance , which is very convenient.
In addition, this method, whether it is a digital table or a pointer table, is common. As long as you master the method and follow it step by step, it is not difficult to determine the first and last ends. Find a pointer multimeter (a digital meter is also available, but the number jumps a lot, so pay attention to the amount of change), first use the resistance file to find out the three sets of windings, this is easy, just measure the on-off directly, there must be resistance is one group, and the infinity is another group.
Then use the AC mA file to distinguish the first and last ends of a winding, which is essentially the confirmation of the end with the same name. According to the design of the motor, connect the wires according to the figure below. If the wiring is correct, there will be a little residual magnetism when rotating, and it will emit a little electricity when rotating. At this time, the three phases are balanced, so the multimeter is equivalent to the zero line. It should not be There is current passing through it.
Through this method, turn the head and tail of the winding several times, and finally you can determine the labels on the windings U1-V1, V1-V2, W1-W2, and then re-mark them.
