@norder Great! Thanks!

@dc42 There was no info like "Phase A short to ground" on Panel Due, usually there is.
We've never experienced such problems not related to hardware issues you describe, on 3.5RC firmware.
I know them well because they occur when reconnecting extruder motors to the toolboard and damaging wires / pins.
We roll back to 3.5 RC3 and see what happens.

I don't want to do this because the machines are all sheetmetal and if somebody accidentally connect mains + to mains - on the power supply, while assembling or servicing, it could end up unwell.
So we grounded every printhead, cried over stupidly damaged toolboards and PT1000s, and went on !

Thanks and sorry for replying after weeks

We run 14 (MB6HC) machines on 3.5RC3 firmware, for months, without problems, we do not ever turn them off.
I updated 2 of them to 3.6 RC3.
After hours of idle, I tried to print something and noticed that one of the motors (a co extruder connected to MB6HC driver) vibrates instead of extruding.
I restarted the machine and the problem went away.
The second one was merrily printing until in a random moment a Z motor started to vibrate (like phases being messed up) instead of moving the bed up and down. This was a serious thing, which could easily lead to a disaster.
Again after a restart, everything went back to normal.

Both machines were operating correctly on 3.5RC3 for a long time.

Please correct if I'm wrong, we do not have PSU PE and V- connected, so the toolboard will not be grounded this way.
The toolboard, extruder motor and hotend are mounted to a metal X carriage plate.

To ground the printhead correctly, this metal plate should be connected to global machine PE (machine frame) at common point right ?

The only problem could be PTFE tubing accumulating electrostatic charge, would it be enough to connect it to the carriage, or should it be wrapped with copper shielding ? There are meters of it ...

Thanks, it looks like a good idea to read the docs eventually

We have a long story of failed toolboards.
5 pieces of 1.2A version with different errors like wrong temperature readout, unable to connect or not extruding.
1.3 are much better, but today the second one went bust out of the blue with :
"Error: Expansion board 121 stopped sending status"

I'm not here to complain or rant,
although I hate them with passion due to microscopic connectors and cables in all directions :).
We definitely will be using them forever as they reduce cable mileage.

The question is are there any safety concerns while connecting them, maybe there is a surge from 3m PTFE tubing or something alike. I assume they operate in suboptimal conditions which cause problems.
I just don't know what can be possible errors with mounting/wiring ?

I'd like to revive this subject as can you share some experience?

We are building a large coreXY with 4 XY motors (nema 17 60mm)
I wonder if there are any reasons not to connect two motors to one driver?

The drivers are 4.5A so there is some overhead and the setup will be 48 V. We used nema 23 with one driver on Duet 2 ethernet but only on Z axis so they have much less to do and worked for years without problems, but this time they are on XY and there will be a lot of long fast travels.

@dc42 Thanks a lot David, I should definitely forget it

Is it possible to resolder a MOSFET and a few small warehouses on the board to be able to apply 48 V or should I forget it ?
We have a fair amount of older MB6HC on large machines and 48 V would greatly help with long fast travels.
I'm aware we can order new Duets or expansion boards.

@sebkritikel Thanks, I'm concerned only about the motor characteristics of servos / steppers.
With fast long travels steppers have very little torque and are troublesome.
But on the other hand step dir is not a perfect solution to drive servos also.

There is little info about these subjects so probably we will go all Duet to save time and trouble.