Ready Steady Eddy

[EddyCurrent]

@cncJim more reading regarding the 4 safety categories, once the risk assessment identifies the required safety category only then can the correct hardware be selected.

http://www05.abb.com/global/scot/scot209.nsf/veritydisplay/b98cfaed98af7397c12573ad00471f6a/$File/2CDC110004C0205_03.pdf

It's correct when m_c says the components are selected to minimise faults such as contact welding, also if a failure does occur then a restart should not be possible. For example if a contactor was used to remove power form the VFD then it should have a normally closed auxilliary contact in series with the safety relay reset button to ensure the contactor is de-energised or not stuck closed by contact welding and I could do that with my K1 for the stepper driver power.
As I said in a earlier post the drawings I have put on here are for my machine and anyone else needs to carry out their own risk assessment for their machine. At the end of the day as JAZZCNC pointed out none of this is strictly required for a DIY machine for use at home because the legislation does not apply to domestic situations but my theory is that for the little extra involved we might as well go the extra mile and make it as good as it needs to be. Because the VFD I'm using has the STO feature means I have decided not to use a contactor to cut power once the safety relay times out, if it did not have this feature then I would have used a contactor.
So the correct procedure is to risk assess the machine to identify the required safety category then design the safety system to meet that category both by choice of appropriate components and how those components are connected together.
I would be very surprised if the type of breakout boards we are using would meet the requirements of a safety system but this is the only means of telling the computer that things have stopped (as far as I know) but if other things come into play first such as cutting power to moving parts or making moving parts safe then it might not matter what the computer is trying to do as it's commands are falling on deaf ears so to speak.
Plus I realise all this procrastination on my part is just putting off the mechanical build part of my project