Quote Originally Posted by cropwell View Post
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.!