If releasing Start stops the circuit, inspect the holding branch. If Stop cannot interrupt it, find the path bypassing Stop. Fix one thing and retest instead of changing the entire circuit.
1. Describe exactly when the circuit fails
Instead of “the circuit does not work,” write “pressing Start energizes KM1; releasing Start de-energizes it.” Those extra words narrow the fault to the transfer from the Start path to the holding path.
KM1 is the name assigned to the contactor. Its coil picks up when powered, and its auxiliary contact should change state with it. Observing these parts separately helps distinguish a missing electrical path from a missing device link.
Before making changes, note three things: which action you took, whether the coil picked up, and whether the auxiliary contact closed. Send those details with the drawing when asking someone for help.
2. Use the symptom to choose where to look
Not every fault comes from the holding branch. If Start never energizes the coil, inspect the supply path first. If it picks up but will not hold, focus on the holding branch.
This table suggests where to start tracing. It does not imply each symptom has only one possible cause.
| What is the circuit doing? | Where should you look first? |
|---|---|
| Runs while Start is held, stops on release | The KM1 auxiliary contact branch in parallel with Start. |
| Pressing Start does not energize the coil | Supply, Stop, the path to the coil, and the supply return. |
| Pressing Stop does not release the coil | Any branch taking power from before Stop. |
| Coil energizes as soon as power is applied | Whether Start or the holding contact is already closed. |
| Coil picks up but the auxiliary contact does not change | The symbol type and KM1 tag in device properties. |
3. Stops on Start release: inspect the holding branch
While Start is held, current flows through Start to the coil. Releasing it opens that path. To keep the coil energized, current must pass through the closed KM1 auxiliary contact.
Check whether the auxiliary contact closes when the coil picks up. If it stays open, check its tag and contact type first. The coil and contact must link to the same device; the holding branch uses a normally open (NO) contact.
If the contact closes but the circuit still will not hold, inspect both branch endpoints. It must run from after Stop to before the coil, in parallel with Start. Zoom in on each terminal: an endpoint near a terminal may not actually be attached.
- Press Start and observe the KM1 coil and auxiliary contact.
- If the contact does not close, check the KM1 tag and select a NO contact.
- If it closes, check both wire endpoints of the holding branch.
- Correct the fault you found, then press and release Start again.
4. Stop does not work: find the bypass
Stop must sit before the split into the Start and KM1 branches. Opening Stop then removes power from both.
A common mistake is feeding the holding branch from before Stop. Current can still flow through KM1 to the coil even while Stop is pressed. Stop appears in the drawing but cannot interrupt that path.
Trace each path from the supply to the coil. Any path that does not pass through Stop needs inspection. If real equipment cannot stop, put it into a safe state before checking; do not alter live wiring.
5. Starts immediately on power-up: find the closed contact
Initially, Start is released and the KM1 auxiliary contact should be open. If the coil picks up anyway, an unintended closed path is powering it.
Check whether Start is held, the holding branch incorrectly uses a normally closed (NC) contact, or a wire directly feeds the coil. In EleRun, inspect button states and device properties; with real equipment, also check the physical contacts.
Do not add another contact merely to block the unwanted start. Find and correct the unintended supply path first.
6. After fixing it, test starting and stopping
Have you fixed the drop-out on Start release? Test Stop next. A holding branch fed from the wrong point may now hold but fail to stop.
Repeat the sequence: apply power without pressing anything → press and release Start → press and release Stop. Expected behavior: initially idle, holding after Start, then stopped and waiting for a new command after Stop.
Record the fix in one short sentence, such as “KM1 branch endpoint was not attached to its terminal; reconnecting it restored holding and stopping.” This gives you specific experience to reuse next time.
ELERUN LAB · TRY IT YOURSELF
Same symptom, two different faults
Start with a working holding circuit. Save a separate copy so you can return to the baseline, and change only one thing per run.
- First run: change the KM1 auxiliary contact's tag to KM2. Second run: restore KM1, then disconnect one end of the holding branch.
- Both may stop when Start is released. How does the auxiliary contact's state differ between the runs?
Compare your reasoning
With the wrong tag, the contact does not follow the KM1 coil; inspect symbol type and tag. With a broken wire, the KM1 contact can still close when the coil energizes, but the holding path is incomplete; inspect the terminal connection. The same symptom can have different causes.
Record what you actually observe in your drawing. Check may identify some faults, but Run and tracing the path distinguish them.
7. Frequently asked questions
What if the contact still does not close with the same KM1 tag?
Check the symbol type and its simulation capabilities. Matching tags link compatible devices; they do not turn an arbitrary symbol into a suitable auxiliary contact.
If Check reports no faults, is the circuit correct?
That alone is not enough. Operate the required sequence. Check detects faults within the tool’s scope; you still need to compare behavior with your requirements.
