Aiph5u
August 12, 2023, 3:43am
8
Hey Tom,
I would assume that PwnCNC’s cable is shielded and grounded, however it is important for the ground of the VFD to be connected to ground on the wall outlet/wall box. This is usually done inside the IEC 60320 power connector and inside your AC power plug . Internally, usually the ground symbol (⏚) is the grounding point of the VFD. This point has to have a connection to the power plug internally, and then to the PE wire and the shield of the spindle motor cable.
On the entire setup, it is important that basically, all the ground wires should converge in one point , and that’s in the control cabinet usually at the one screw of the metal housing part of your VFD, which is also marked accordingly (⏚).
Here I put together grounding information . Note that besides grounding the VFD, the spindle, and the Controller, it is also necessary to ground the frame and all moving parts of the frame . I have described the parts and tools needed to ground the frame here .
The spindle cable shield should always be connected at both ends. At the spindle end it should be connected to the connector housing internally, and the connector should not allow it to be connected any other way. Here you can see how the cable shielding is connected inside spindle connector (figure 3, see “PS2”).
Furthermore, I would not recommend anyone to connect a spindle cable without having read this document carefully:
Even electricians usually have not this knowledge since it deals with shielded power cables.
In many cases, the grounding of the VFD is connected to the metallic part of its housing, but you have no guarantee that this is the case. Usually the ground symbol (⏚) is the grounding point of the VFD.
A VFD is designed to be installed in a metallic grounded control cabinet, such as the one shown below. Such a cabinet has a steel mounting plate that you can remove and mount the VFD on, and the whole enclosure is grounded.
Usually it’s not only the VFD that finds its place here, but also many other things you probably want to use .
How the VFD is connected to ground is described here in Figure 2 . There you also find the answer what to do with the VFD end of the spindle cable shield: It should be clamped to the mounting plate with a cable clamp or grounded with a grounding cable gland .
Basically, all the ground wires should converge in one point, and that’s in the control cabinet usually at the one screw of the metal housing part of your VFD, which is also marked accordingly (⏚).
If the metal part of the housing of your VFD is not connected to its ground terminal internally, then you should run a ground wire from this ground terminal (⏚) of the VFD to the steel mounting plate by screwing in a ground connection lug there as close to the VFD as possible, and run all the ground wires together there. From the ground at the VFD on the mounting plate, the ground wire in the power input cable goes to your wall box or your room’s electrical panel, and it’s also from the ground at the VFD that the ground goes to the spindle (the yellow or yellow/green PE wire ) as seen below.
Note that even if PE wire and cable shield are both connected to ground, they serve two different purposes. PE is crucial for electrical safety, and shield cannot replace the PE wire.
If you bought a cheap Chinese spindle, you should also be sure that in the spindle the PE (fourth) pin of the spindle socket is actually connected internally to the spindle housing, as seen here . You can check this with a multimeter (set to ohms/resistance, the resistance between the PE wire and the housing of the spindle must be close to zero).
You would have to make completely new cables. I described some of the thoughts for this here .
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