# Mag Switch For HY VFD?

**URL:** <https://forum.onefinitycnc.com/t/mag-switch-for-hy-vfd/28858>\
**Category:** Spindle/VFD (Aftermarket/Unsupported)\
**Created:** [October 3, 2024, 2:53pm UTC](https://forum.onefinitycnc.com/t/mag-switch-for-hy-vfd/28858 "2024-10-03T14:53:51Z")\
**Posts on this page:** 1\
**Showing post:** 2

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**Author:** ![349iq2345](https://avatars.discourse-cdn.com/v4/letter/3/bb73d2/32.png) [@349iq2345](https://forum.onefinitycnc.com/u/349iq2345)\
**Post date:** [October 3, 2024, 3:27pm UTC](https://forum.onefinitycnc.com/t/mag-switch-for-hy-vfd/28858/2 "2024-10-03T15:27:17Z")

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Hey John,

a magnetic contactor in the supply line of a VFD is recommended, because it prevents the VFD coming up in spindle RUN mode after a power outage. What they usually mean, is that DON’T EVER USE a switch or magnetic contactor in the supply line of a VFD to switch between spindle RUN and STOP. This can indeed damage the VFD and the spindle.

**The ONLY WAY to stop a running spindle, is the STOP command of the VFD** , either from keypad in keypad mode, from intelligent terminal if in terminal mode (like used with the MASSO G3 CNC Controller) OR by a Modbus command (like used with the [buildbotics.com](http://buildbotics.com) and Onefinity Original/PRO/X-50 Controller).

The usual [VFD control cabinet](https://forum.onefinitycnc.com/t/hey-is-this-your-vfd-enclosure/10130/3) is wired so that

1. a **switch or magnetic contactor** enables power to the VFD and the other components,

2. a big red mushroom-shaped **Emergency Stop button** is wired to a [ISO 13849](https://en.wikipedia.org/wiki/ISO_13849) [Safety relay](https://en.wikipedia.org/wiki/Safety_relay) like the [Omron G9SE](https://industrial.omron.co.uk/en/products/g9se) ([datasheet](https://assets.omron.eu/downloads/datasheet/en/v3/j198_g9se_safety_relay_unit_datasheet_en.pdf))

3. Finally it is mandatory that the setup when in Emergency Stop mode can only come back to spindle run mode after having pressed a **Reset button**. A possible [Wiring is shown here](https://forum.onefinitycnc.com/t/emergency-stop-issue/8441/4). Usually the safety relay is wired so that when Emergency Stop is pressed, not only the spindle is stopped, but also the g-code program running in the CNC controller is paused and the machine is led to a safe mode (and stays this way until you press the reset button).

> [@Proper Grounding; How have you grounded your frame?](https://forum.onefinitycnc.com/t/proper-grounding-how-have-you-grounded-your-frame/12331/22):
>
> [![Mechatron_Control_Cabinet__Door_and_Interior_with_door_back_50pct](https://us1.discourse-cdn.com/flex022/uploads/onefinitycnc/original/3X/2/a/2a7bbeeaeb63d8233345cb1b12a538de449e6832.png)  
> ](https://forum.onefinitycnc.com/t/hey-is-this-your-vfd-enclosure/10130/3)  
> _Image: VFD Control cabinet. 1. power switch, 2. Reset button 3. Emergency Button_
> 
> ![Mechatron_Control_Cabinet_AB022-HF-V1-ATC](https://us1.discourse-cdn.com/flex022/uploads/onefinitycnc/original/2X/5/5aa2a0be31d1796e5c75194e4add9ac475596a25.jpeg)

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