Electronics for New Machine + Chinese Spindle + VFD

[cropwell]

Clive answered eveything but I'll just check on this.?



If you are running wires to Star Earth point then the cases being connected shouldn't matter because your not using them for Earth. You should however tie them to the Star Earth for safety in case of short circuit.

The whole point about Star earthing is that it avoids earth loops. If you have shielded wires in a earth loop, you can get a current flowing in the shield due to different magnetic fields at places in the loop. This will act as half a transformer, with the signal wire being the other half. This could generate spurious signals and affect the machine in unpredictable ways. In audio applications, with high impedance inputs to pre-amplifiers, this is immediately obvious as hum.

It does no harm to earth cases, in fact from a safety point of view, it is essential. I would also protect the mains input to the box(es) with an RCD. 30ma up your arm for 10 milliseconds is a lot more pleasant than it going up in smoke !!

From the safety aspect - if your Estop is a NC switch then any break in the circuit signals as an Estop condition. A NO system, if it fails will not show a fault and not work when you need it.

[JAZZCNC]

The whole point about Star earthing is that it avoids earth loops. If you have shielded wires in a earth loop, you can get a current flowing in the shield due to different magnetic fields at places in the loop. This will act as half a transformer, with the signal wire being the other half. This could generate spurious signals and affect the machine in unpredictable ways. In audio applications, with high impedance inputs to pre-amplifiers, this is immediately obvious as hum.

It does no harm to earth cases, in fact from a safety point of view, it is essential. I would also protect the mains input to the box(es) with an RCD. 30ma up your arm for 10 milliseconds is a lot more pleasant than it going up in smoke !!

From the safety aspect - if your Estop is a NC switch then any break in the circuit signals as an Estop condition. A NO system, if it fails will not show a fault and not work when you need it.

Rob I'm not getting the point of that post.? . . . . Do think I'm saying some thing different to what you are.!