Re: I Quit

"Jim Wilkins"  wrote in message news:v6a5iu$3gpk6$1@dont-email.me...
Here are some of the terms and concepts of relay control logic. Hopefully I didn't confuse anything, I'm nearly as old enough to be President so writing this was a memory test.
Latching Relays have an internal magnet that retains the energized position until a pulse of opposite DC polarity overrides the magnet and returns the relay to de-energized. Thus they remember their On or Off state through a power loss and could select which of two compressors to use. Non-latching relays in pairs can also remember their state as long as they remain powered.
Relay  "Form"
https://forum.digikey.com/t/understanding-form-a-form-b-form-c-contact-configuration/811
The equivalent naming for switches is SPST, SPDT, 3PDT plus ON/OFF, ON/ON, ON/NONE/ON for single or double throw and center off. Your simplest manual control would be 3PDT center off, for instance a fwd/off/rev drum switch, rewired to feed power from the original motor contacts to either compressor.
3 wire control
https://eepower.com/technical-articles/understanding-three-wire-control/#
It prevents machines from starting automatically all at once after a power outage, if that would be dangerous or trip the breaker.
Controls commonly operate from a 24VAC "control transformer", check the coil voltage as well as contact rating when buying surplus.
Ladder logic.
https://control.com/textbook/relay-control-systems/relay-circuits/
CR = Control Relay, contact rating of 10A or less, vs a CONtactor with higher rating for motors.
Only the labels indicate the relation between coil and contacts, dotted lines would become too confusing in a large schematic. Being able to decipher and understand a complex drawing was job security.
Confusingly, solid state diodes were once called CR for Crystal Rectifier, to distinguish them from 2 element vacuum tubes.
All wires are labeled at both ends with Brady number markers, otherwise hopeless confusion is inevitable. Numbering instead of color coding saves on wire cost. The standard for General Motors equipment was 16 AWG or larger, too strong for ham-handed or disgruntled union workers to "accidentally" break.
The incoming power line is L1, L2, L3 with numerical prefixes added when they pass through a breaker, fuse etc, so 1L1, 2L1, 3L1.
The wire is stranded MTW, Machine Tool Wire, with pull-tested crimp lugs on the ends. Ring terminals are safer, forks more convenient. Stranded wire resists vibration better than solid. To run wires onto a hinged control box door, the bundle runs vertically along the hinge side to minimize flexing.
Relays can be lined up in a tight row on DIN rail with space between rows for the wire harness. The red button operates the relay manually for testing. A separate back panel spaced out from the back of the enclosure simplifies drilling and bolting. Greenlee sells a 1-7/32" punch for standard sized panel controls and indicators, should you stumble onto a surplus batch of them.
Current Transformer
https://en.wikipedia.org/wiki/Current_transformer
They detect the AC current in a wire through its insulation, without any physical connection to its voltage, the same as a clamp-on ammeter but without batteries to replace. I have them with LED indicators to set the thermostats on two electric baseboard heaters I use for automatic backup to wood heat.
https://www.digikey.com/en/products/detail/cr-magnetics-inc./CR2550-R/1045159?
This PZEM-061 is on my 240V air compressor to show the run current and total power consumption, or for any other 240V device I'm testing.
https://www.amazon.com/HiLetgo-Multimeter-PZEM-061-Voltmeter-Transformer/dp/B079JNY5VD/
The company where I designed relay controls closed and I moved on before PLC controllers came out.