# Mag Switch For HY VFD? **URL:** \ **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:** 4\ **Page:** 1
**Author:** ![jnordyke](https://sea2.discourse-cdn.com/flex022/user_avatar/forum.onefinitycnc.com/jnordyke/32/1881_2.png) [@jnordyke](https://forum.onefinitycnc.com/u/jnordyke)\ **Post date:** [October 3, 2024, 2:53pm UTC](https://forum.onefinitycnc.com/t/mag-switch-for-hy-vfd/28858/1 "2024-10-03T14:53:51Z")
After an oopsie while moving my CNC, I have to replace my HY 2.2kw VFD. As I review the manual for the new VFD, I see this in the section on wiring: “Note: Do not use the electromagnetic contactor as the on-off button of power supply for the inverter.” Why not? I have a powertech MP18 magnetic switch like those used on 3hp table saws between the mains and a receptacle into which the old inverter was plugged. Used it almost daily for 2 years. Was I in some kind of danger, or potentially damaging the inverter?? ---
**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")
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) ---
**Author:** ![jnordyke](https://sea2.discourse-cdn.com/flex022/user_avatar/forum.onefinitycnc.com/jnordyke/32/1881_2.png) [@jnordyke](https://forum.onefinitycnc.com/u/jnordyke)\ **Post date:** [October 3, 2024, 3:32pm UTC](https://forum.onefinitycnc.com/t/mag-switch-for-hy-vfd/28858/3 "2024-10-03T15:32:28Z")
Thanks. The manual could have been much clearer on this point. I am relieved that my practice of the last 2 years was not tempting the fates. ---
**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, 3:57pm UTC](https://forum.onefinitycnc.com/t/mag-switch-for-hy-vfd/28858/4 "2024-10-03T15:57:45Z")
Hey John, hey all, here the corresponding excerpts from good VFD manuals: ![Hitachi_WJ200_Manual__Electromagnetic_Contactor_on_VFD](https://us1.discourse-cdn.com/flex022/uploads/onefinitycnc/original/3X/8/c/8c4efca89847e329ca0e5029e4e842981e37c9ad.png) _– Source: [Hitachi WJ200 Instructions User Manual (PDF)](https://www.hitachi-iesa.com/sites/default/files/supportdocs/WJ200_Instruction_NT325X.pdf)_ ![Omron_MX2_Manual__Electromagnetic_Contactor_on_VFD](https://us1.discourse-cdn.com/flex022/uploads/onefinitycnc/original/3X/b/3/b3091c7714e54bd7b2846e7896f93de6a215de88.png) _– Source: [Omron MX2 Users Manual (PDF)](https://assets.omron.eu/downloads/manual/en/v5/i570_mx2_users_manual_en.pdf)_