Mesa 7i97t

 I'm having an intermittent issue with a Mesa 7I97T on a Raspberry Pi 5. Occasionally CR7 comes on and stays on until I reset the board.The 7I97T is powered by a Mean Well 5V PSU with no earth connection. The 5V negative is floating, and I measure about 100VAC between 5V- and cabinet earth.Does anyone know what specifically causes CR7 to latch on like this? Is there anything in HAL/HostMot2 I can log to find the cause?Also, should the 5V negative normally be bonded to cabinet earth, or left floating?
Thanks all!

I am configuring my CNC with a 7i97t, but I don't have that problem. I have a Mean Well 5V 10A power supply with a ground connection for the Mesa and the Raspberry Pi 5; the Mesa needs to be grounded near the RJ45 jack, where it is marked "frame ground."

Just for safety, and noise I would ground the 5V common.

The Init LED can illuminate for power related issues (check the 5V at the 7I97T)
With power related issues, the Init LED typically blinks.

The other cause of the Init LED being illuminated is because the watchdog
has bitten. This usually indicates either a latency issue with  the host, some
general communication fault or the watchdog timeout set too low in the hal file.

flyingbrick wrote:

... and I measure about 100VAC between 5V- and cabinet earth.Does anyone know what specifically causes CR7 to latch on like this?

The answer to your question is there in your question, 100VAC is way to much interference, so the grounding is non existent if that is happening inside a metal box.
Does the shop have proper grounding and a ground fault interrupter?
Is the machine grounded through the mains cable, properly on both sides?
Is the power supply grounded to machine/control box ground?

So, is it best to ground the 5V and 24V negatives?

In general I lack experience in this stuff, ground loops especially are confusing. I didn't want to ground the 5v negative and create some other issue. According to what I could find online, the floating 5v is fairly normal (switch mode power supply).

Yes the case etc is ground, just 5v is floating.

Thanks pcw, will ground.