Circuit Negma

C++, C, VB.NET, PCB, Electronics, Circuit Design

How to test three-phase devices

Posted by Circuit Negma on March 28, 2006


How to test three-phase devices

Three-phase pumps, compressors, and the like, must be connected in proper phase sequence to avoid damage. Typically such devices will draw less current when connected wrong, and can be easily checked with an amprobe (clip on ammeter) for current draw. For example, testing an air conditioner that has a scroll compressor, one will find that if it’s hooked up in the wrong phase sequence, it will draw too little current, and thus any two wires can be switched to change the phase sequence.

There are special small pocket sized motors that are used to check phase sequence by checking the direction of rotation of the motor. These are expensive. A cheaper alternative is to use three neon lights, and whip the head (or eyes) in a quick motion past them to see which way the phase sequence is going.

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