Level 1 — Guided Motor Starter

Goal

Switch the PLC to RUN, then press Start. The rung seals in through M1’s front aux block 23–24 (M1_Aux on IN-3). Press Stop, press the E-Stop or trip the overload to drop the motor out. Then try it with Start held: hold the green Start button on its picture while you release Stop or the E-Stop, or reset the overload — the supplied program’s restart permission keeps the motor stopped until Start is released and pressed again.

Stop circuit

The E-Stop’s first contact block (11–12, N.C.) and the overload’s 95–96 (N.C.) are wired in series with the contactor coil: OUT-0 → 11–12 → 95–96 → A1. Either one drops the contactor whatever the PLC program is doing. The E-Stop’s second block (21–22) and the overload’s 97–98 only report to the PLC, so the program can withhold its command until the operator restarts deliberately.

What this lesson does and does not show: releasing the E-Stop does not start the motor by itself: the contactor’s seal is lost, and the Start_Permit rung withholds the command until Start has been released and pressed again — even if Start was held through the release, a Stop, an overload reset or a power return. This is ordinary PLC logic with a two-contact E-Stop, not a safety-rated circuit: a welded contactor or a failed output is not detected. Where the risk assessment calls for it, a monitored safety relay does this job (Level 6). The ordinary Stop drops the permission too, so a Start held through a Stop does not restart the motor either. So does M1 dropping out by itself after a confirmed run (its output lost DC-0(+) or RTN OUT-0, a wire came off): rung 0 remembers that M1 had pulled in, so when M1’s aux contact opens while the command is still on, rung 1 takes the permission away and the motor does not restart when the supply returns. This program has no timer: a start pressed while the output has no supply waits as long as Start is held (Level 2 adds a 150 ms pickup check that aborts it); a momentary press leaves nothing pending. The overload’s 97–98 is N.O., so if its status wire is broken the PLC cannot see a trip — 95–96 still stops the motor, but check that input when you commission the panel. A short on the 24 V supply drops the field inputs and the output, but not the controller: the rack has its own supply (the PA72 on 120 V). A wire from +24 V to a PE terminal is the same short, because 0 V is bonded to PE. If the output OUT-0 switches onto a short, the OB16E’s electronic fuse turns its group off and stays tripped until it is reset (Reset fuse, from Logix Designer online); this trainer refuses that reset while the program still commands the output on. If M1’s aux contact makes the short, this trainer holds the 24 V supply off until you rewire or switch the panel off and on. The controller’s start-up after a power loss is shortened to 4 s here. A short on the 120 V or 480 V side opens the protection in its path: on the motor’s branch that is F2–F4, and only the motor loses power; anywhere else it is the protection ahead of both supplies (F1, F5/F6 or the feeder’s own), so the controller loses power too. Which device opens first in a real panel depends on how the protection is coordinated. This trainer keeps it open until you lock out and restore power, which stands for finding the fault and replacing the fuse.