WiremanWireman · Motor runs only while start is held: troubleshooting for electricians · 2023 NEC ·
Motor runs only while start is held
The holding contact isn’t sealing the start button in. Find out whether it’s the contact, the wiring or a jog setting.
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How it works
In standard 3-wire start/stop control, the start button is momentary. A normally open auxiliary contact on the contactor (often marked 13 and 14) is wired in parallel with the start button. When the contactor pulls in, that contact closes and keeps the coil fed after you let go. If the motor drops out on release, the seal-in path is open or wired in the wrong place.
Every question and answer in this guide. Tap “Step by step” to walk through it.
- Is there a run/jog selector or a jog button on this control?
- Yes, and it’s in JogIt’s in Jog, so this is normal
- Yes, it’s in RunDid this ever work, or is it new or rewired?
- New install or just rewiredThe holding contact is wired in the wrong place
- It used to workTest: Check the holding contactExpect: OL at rest, near 0 Ω with the armature pushed in, and every wire tight.
- Stays OL when pushed inFailed auxiliary contact
- Closes fine, but a wire was looseLoose wire in the seal-in circuit
- Contact and wires are goodTest: Watch the coil voltage at releaseExpect: Full coil voltage while held, and control voltage on both sides of the holding contact.
- Voltage on only one side of the aux contactThe holding contact is wired in the wrong place
- Coil voltage low or saggingWeak control voltage
- Something else opens at releaseAnother device opens when start is released
- No jog functionDid this ever work, or is it new or rewired?
- New install or just rewiredThe holding contact is wired in the wrong place
- It used to workTest: Check the holding contactExpect: OL at rest, near 0 Ω with the armature pushed in, and every wire tight.
- Stays OL when pushed inFailed auxiliary contact
- Closes fine, but a wire was looseLoose wire in the seal-in circuit
- Contact and wires are goodTest: Watch the coil voltage at releaseExpect: Full coil voltage while held, and control voltage on both sides of the holding contact.
- Voltage on only one side of the aux contactThe holding contact is wired in the wrong place
- Coil voltage low or saggingWeak control voltage
- Something else opens at releaseAnother device opens when start is released