Suppose for example that the motor is connected in Star. A permanent connection is accomplished with 2 or 3 metallic bridges. This is usually done if the motor is small (smaller than 3.5 KWatts) or if the motor is driven by an inverter or some kind of electronic driver. A permanent connection is when the motor is connected in either Star or Delta, and this connection is not supposed to changed during the operation of the motor. The answer is simple: To easily bridge a permanent connection. You may now wonder, why the coils are connected in cross-pattern and not vertically. Instead, the pairs are in cross-pattern like this: It sounds logical to separate these 3 pairs in a vertical pattern, but that's not the way it goes. Since each coil has 2 endings, it is easy to understand that these six leads can be separated in three pairs, and each pair is connected to one coil. Here is a photo from a typical electrical connection box:Īs you can see, there are indeed six leads arranged in two rows. First of all, you need to understand how the coils are connected with the six motor leads that exist in the electrical connection box. Two or more coils short-circuited with each other (current leaking from one coil to another coil)Īll of the above problems can be detected with a simple Ohm-meter.Leaking coil to ground (current leaking from one coil to ground/neutral).Short-circuited coil (less than normal or zero coil resistance).There are basically 4 problems that the motor windings can suffer from: If someone works with AC 3-phase motors, then it is important to know how to connect these motors in Star and Delta connection, and how to detect an electrical problem. It is called squirrel-cage, because it's rotor looks like the exercising wheel found in squirrel or hamster cages.Ī typical 3-phase squirrel-cage motor has six connection leads in the electrical connection box for the three coils. The most common type though is the -so called- squirrel cage rotor. The rotor of a squirrel-cage motorThere are several different AC motor types, each one with different operating and mechanical characteristics.
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