Thank you Rob and EddyCurrent. I will have a look at NVR's and I didn't realise that I would need to a switch to reconnect the limit circuit to enable me to jog off from the error position. Am I correct in saying that the HG07 BOB will recognise a 0v or 5v line with a max 5mA? The HG07 data sheet says very little about the inputs.

EddyCurrent, you mention that I have the proximity sensors wired correctly to a point! What do you mean by that?

Is there a benefit to giving MACH3 a separate input for limits and emergency button, can MACH3 act differently? I suppose from my point of view I had the limit switches as just that, a last line of defence after soft limits, the emergency switch is a "oh my god" I am being eaten by the machine Stop everything NOW with no software involved.
Simon