The scenario
A star-delta starter control circuit needs to prevent simultaneous energization of the star and delta contactors while providing visual phase-status indication from all three incoming lines.
What is in this drawing
Read the decisions behind it.
01
Use NC auxiliary contacts from each contactor in series with the opposite coil for electrical interlocking
02
Add a seal-in contact across START to keep the main contactor energized after release
03
Include three phase indicator lamps connected phase-to-neutral for clear supply presence visual feedback
Reusable for industrial motor starters where two contactors must be mutually exclusive, with phase supervision lamps on a three-phase supply.
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