Earthing of a controller box of CNC machine in TN-C(TN-C-S) system of supply 230 V AC

[Hristo]

Hey guys,
My name is Hristo, I am from Plovdiv, Bulgaria.
I have tried to make my first hobby cnc machine, but my experience of electronics is very small.
I have a question about Grounding, Earthing. I have to note before, that our building is old, and there
are only 2 conductors, and we have not separate conductor for Earthing unfortunately. This system
is TN-C and TN-C-S. In this case, we have to use “neutral” for this kind of Earthing.
The main elements of electronic are: Arduino Uno; 3 steppers-NEMA 24- 3,1 N.m; 3 stepper-drivers-
SH-750- 5A, PSU-s - one 36V DC for steppers, and other - 12V DC for fans, (5V for Arduino from
computer‘s USB).
I will not use a VFD for motor-spindle. I have intention to use routing motor-spindle, and I will
connect it directly to 230 V- AC, and will be no connection to controller.
I will Grounding 2 PSU by “neutral” in “star” point (in TN-C-S system), but I am afraid to connect
in this “star” point stepper drivers (GND) and Arduino (GND). I think, that it will be too risky.
To install separate ground rod is not easy task.
What do you think about this situation ?
Best regards

[harmo]

Hi Hristo,

That's an interesting question. We run a TNS system here in Australia, and many other users here will be only familiar with the systems used in their countries. So I'm not sure how much help we'd have here. We definitely don't want you to get hurt or burn your building down because you tried to do something you weren't confident in.

I'm afraid I don't know enough to talk about a TNC-S grounding. I only have a very basic understanding on the setup. But if I recall correctly, it involves attaching the earth to the neutral wire.... that's not something your average CNC hobbyist is qualified to do.

I'd recommend that you talk to a local electrician for that, as they'd know the safe and legal (for your country) way to do that, as well as ensuring you have the best possible solution. Adding an earth line would be the safest option. The TNC-S setup has more risk because if there is a fault somewhere on your neutral line (you mentioned your building was old) then ANYTHING "earthed" to your neutral would become live, and pose a real hazard.

However, before you call the electrician, you said that you are new to electronics, so I just want to make sure you understand something.

Typically, the AC earthing is done on the AC side of your DC power supplies. If you use the TNC-S setup, the computer power supply, and the 36V and 12V power supplies will all have AC earth inputs that can handle the earthing should they need to. Do not connect DC "GND" terminals on the Arduino to AC Earth... they're not the same thing.

For wiring stepper drivers and arduino in a DC configuration, have a look at this:

https://www.youtube.com/watch?v=iY_4...oneBotWorkshop

If you go the 15:45, you'll see the standard DC wiring. Note the lack of earth connection.

It gets confusing when many stepper drivers can be powered by either AC or DC power. Make sure you follow the correct instructions for your setup.

Good luck!
Harmo

[Hristo]

Harmo,
Thank you very much for your advice.
Best regards:Hristo

[dazp1976]

The earthing in a lot of our domestic environments are made up of just a big long metal spike smacked through the floor deep into the dirt.