Grounding and probe

[ryghar]

Hello!

Reading about proper grounding of cnc electronics I saw that ground has to be isolated from power supplies negative. So, I have a copper plate with ground cables from 48v, 12v and 5v power supplies with ground cable from the wall.
Everything works fine but the machine itself, has no ground cable because if I attach the negative of my probe cable I will be connecting negative to ground... This morning touching the machine structure and the door handle (the door is metalic) I felt a light discharge. Should I connect the maching to ground? Can this affect in any way the electronics with that negative to ground? ( the discharge was lightly, I can live with that lol)
The router has no ground cable, maybe that was the reason for the discharge.

Thanks!!

[john swift]

double insulated equipment with no earth / ground connection can help avoid problems with ground loops when multiple pieces of equipment are interconnected
but can be present a shock hazard when they use switch mode power supplies
( the leakage current from one supply may be safe but several supplies can add up and be a shock hazard )

I would connect an earth connection to the cncrouter frame
more detail of your system is needed
what are you using as the spindle ?

you may get away with the static discharge but if it finds its way into the control electronics via the limit switches for example it can damage sensitive electronic devices

John

[m_c]

Any kind of metal frame should be connected to earth. It's a basic safety requirement for industrial machines.
John mentions double insulated equipment, but you would really struggle to create a CNC router that could meet double insulated requirements.


However, grounding and earthing can be a bit of a complex issue, but the basic issue is you want to avoid ground loops. That is where the same wire is connected to ground at both ends. An example might be a bit CY signal cable where both ends of the screen have been connected to ground, which can result in current flowing through the screen causing interference in the internal wiring instead of protecting the internal wiring from interference.


My usual wiring practise is to have a central star ground/earth point within the control box (I personally use earth DIN terminals that connect wiring to the DIN rail, but a single stud to the case will also work), which is connected to earth. I then connect all the PSU 0V to the same terminals, so all supplies are connected to earth. I then ensure any shields are connected at only one end (either directly to the case if terminating using glands at the case, or a drain wire to the nearest gnd point - there is no need to run all screen drain wires back to the star point).
Also, if you want to really minimise interference problems, spend a bit extra on a BOB that uses 12 or 24V control wiring.

[cropwell]

Some people think that single phase AC Neutral is synonymous with Ground (Earth). It is not! It is phase neutral for the live, which is one of the three phases used for domestic supply. Different houses in the same street can be supplied from different phases. That, however, is a digression. There is often a voltage difference between Neutral and a local earth. That voltage will depend on several factors. At my house it is 10v. Power supplies can be double insulated, but the output Ground should be connected to Earth, as should the whole machine. In some countries, the Earth terminal on the Mains socket can not be relied on to give protection from shock hazards and so a ground rod is desirable.

[Clive S]

Some people think that single phase AC Neutral is synonymous with Ground (Earth). It is not! It is phase neutral for the live, which is one of the three phases used for domestic supply. Different houses in the same street can be supplied from different phases. That, however, is a digression. There is often a voltage difference between Neutral and a local earth. That voltage will depend on several factors. At my house it is 10v. Power supplies can be double insulated, but the output Ground should be connected to Earth, as should the whole machine. In some countries, the Earth terminal on the Mains socket can not be relied on to give protection from shock hazards and so a ground rod is desirable.

Yes Rob but generally in the UK in towns not necessary in the country The neutral in generally connect to the earth at the consumer unit. Just saying

[cropwell]

Yes Rob but generally in the UK in towns not necessary in the country The neutral in generally connect to the earth at the consumer unit. Just saying

In my house (in the country), the neutral is definitely not connected to Earth as if I short N to E it will trip the RCCB, by causing a Live-Neutral current imbalance of > 30mA. The wiring was brought up to regs about 5 years ago with a new consumer unit.

The OP lives in Buenos Aires* and I do not know the regs in Argentina or the state of his workshop wiring.

*If his flag header info is correct.

Rob-T (just to avoid confusion)