Posted on Feb 4, 2014

Perhaps the most challenging aspect of interpreting ladder diagrams, for people more familiar with electronic schematic diagrams, is how electromechanical relays are represented. Compare these two equivalent diagrams: Also, explain the operation of this motor control circuit. What happens when someone actuates the `Run` switch What happens when t

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hey let go of the "Run" switch The simplest and least expensive style of electric motor control is the so-called across-the-line starter. Describe how this motor control circuit functions, and also define the word G tarter" in this context. Although G¤cross-the-line" motor control circuits are simple and inexpensive, they are not preferred for starting large motors. An alternative to across-the-line motor starting is reduced voltage starting. Identify some of the reasons across-the-line starting is undesirable for large electric motors. A special type of overcurrent protection device used commonly in motor control circuits is the overload heater. These devices are connected in series with the motor conductors, and heat up slightly under normal current conditions: Although the "heater" elements are connected in series with the motor lines as fuses would be, they are not fuses! In other words, it is not the purpose of an overload heater to burn open under an overcurrent fault condition, although it is possible for them to do so. The key to understanding the purpose of an overload heater is found by examining the single-phase (L1 / L2) control circuit, where a normally-closed switch contact by the same name (G–L") is connected in series with the motor relay coil. How, exactly, do overload heaters protect an electric motor against "burnout" from overcurrent conditions How does this purpose differ from that of fuses or circuit...

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