System grounding questions

[Zero Cool]

I am nearing completion of my custom stepper motor controller and i am wondering about proper grounding.

My Mill is a Shibura Roibot. a converted industrial X/Y arm with a modified Z axis. Internally the motors have separate ground wires connected to them then tied together and brought out on one wire. How should the ground for the mill as such be handled? Do I want the Mill ground tie to the motor controller chassis?? Do I need to take a ground wire from the chassis of the mill and the ground wire from the motors and tie them together at the motor controller?? the motors are bolted directly to the mill but maybe 2 wires is needed??

My Motor controller of course has the AC line grounded directly to the chassis of the motor controller box. the PC inputs are all optically coupled so no ground connection between PC and mill except through AC line ground.

 

My spindle motor is a modified Dremel tool running from a PWM controller so it is isolated from ground.

[Tweakie.CNC]

Ideally the Earth and Ground should be treated as two separate circuits.
For obvious reasons all exposed metal parts must be bonded to Earth and this circuit must be regularly tested under health and safety regulations in industry so it makes sense to regularly test the circuit in home shop installations as well.
The Ground (GND) is the signal common return and as there are many signals then the associated GND's should ideally be connected a at one common point at the controller end only. It is important to avoid GND loops and if you are using the PC parallel port then the LPT screen should only be connected at the PC end and the internal wires 18-20 connected via the breakout board to the common GND point. It may also be prudent to use screened / shielded cable for all external wiring runs just to avoid the possibility of future problems.
In the real world this is not always possible but Earth loops and Ground loops are often the source of unwanted electrical noise so avoid them if you can.

Tweakie.

[Zero Cool]

thanks!

[ostie01]

Here, we can refer to neutral and ground

In our 220v electrical box here in Canada, red is the live or hot wire, Black is hot or live too, white is the neutral and earth is the one with no insulation.

110V is one live(black) and the neutral(white) and the earth wire.

All white wires are connected together and black goes to the live side of the outlet( for 110v )

For 220, we use one red and one black (2 X 110v)

Jeff

[Tweakie.CNC]

Jeff,

In Canada, is your neutral (white) at the same voltage potential as the earth wire  ?

Tweakie.

[ostie01]

White is at same potential that the earth wire, only black and red are live wires.

Red and black are to live 110 out of phase so this makes 220v.


Jeff

[NosmoKing]

Here is a good link on bonding and grounding from Siemens.
http://www.automation.siemens.com/doconweb/pdf/840C_1101_E/emv_r.pdf?p=1
All metallic parts of the machine should be bonded to Earth Ground to avoid ground loops.
In Canada the grounded Neutral is a secondary centre tap 120-0-120, in most other parts of the world the supply is 240 to a grounded (neutral) star point of a 3 phase transformer.
N.