Master Motor Control: A Simple Guide to 3-Phase Motor Control

[@ismaeliso]

Great video, covers the main aspects of this important circuit

[@Thequestionis-u3l]

Glad you liked it!

[@Thequestionis-u3l]

If you have any questions about motor control, feel free to drop them in the comments! I'll be happy to help and answer them.

[@kenbobcorn]

Question: why is the neutral for the control circuit the second phase of the 3-phase power? Are the 1amp fuses leading up to the transformer built in? Or specd? Is the second 1 Amp fuse on Rung 1 not redundant since the hot already has a 1 Amp fuse? Great video!

[@Thequestionis-u3l]

Thank you so much for your questions! Let me explain: There's a control transformer connected between two legs of the 480V power and the 120V system. This setup isolates the 480V from the 120V because the primary winding (480V) and the secondary winding (120V) of the transformer are electrically separated. To ensure safety, we ground the neutral on the secondary side. That way, if something inside the panel shorts out to the panel, the 1-amp fuse will blow, protecting the system. The 1-amp fuses on the 480V side are there to protect against a short in the control transformer's primary winding. Without those fuses, if the primary winding were to short out, it would trip the main breaker. The problem then is that we wouldn’t know if the issue is with the motor or the transformer, making troubleshooting much harder. Lastly, some control transformers come with fuse holders but no fuses. Let’s break down how to size the transformer. For example, if you have a 120 VA control transformer, dividing 120 VA by 120 V gives you 1 amp. Sometimes, though, your controls might have more starters and coils, so you’ll need a larger transformer. For instance, a 1000 VA transformer divided by 120 V equals about 8.3 amps. Essentially, you need to size your transformer based on the total amp draw of your controls. Great Questions!!!