By GND I mean the terminal block labelled GND.. (My picture was horrendous so no labels could be seen, apologies.. here's another) That is isolated from the mains earth yes..

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Is that what you are saying too or are you saying not to use that GND?


I was going to use that GND as reference for both the speed control and the relay to turn the spindle off and on (run)..


Is there anything else that is useful to wire into these terminal blocks? Or just speed and run?


(Actually, just spotted it's a 12V OUT that's available.. will I need to put a dropping resistor in or is it ok with 12V?)