The scenario
Two pumps are selected by maintained switches but must never run simultaneously; each contactor's NC auxiliary contact opens the opposite coil circuit when energized.
What is in this drawing
Read the decisions behind it.
01
Use relay_spdt symbols for contactor coils with integrated NC contacts for interlock
02
Maintained selector switches avoid the need for seal-in auxiliary contacts
03
Tie control supply neutral to ground for a single reference net
Reuse for any two-load interlock where only one contactor may be energized at a time, such as dual pumps, fans, or compressors.
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