Three Phase 230V three wire systems

Ok guys, thank you all for the input.

Without leaving myself open and revealing too much private info its a 3phase no neutral 230V supply to DB then single phase 230v feeding the DB for the ESD system. 130V to Earth each phase (no neutral). 6 E-Stops for full engine shut down system all series up so any one opens it opens the circuit and should in theory allow the relay to drop out and stop the engines, fail safe in theory. I would of liked to have seen a double E-Stop circuit so its a positive open when activated as both legs drop out and you dont get false shutdowns should one leg fail but it is not and only one leg so even a loose connection should in theory shut the engines down, again not a good design.

A couple of the cable runs are very long as AJ eluded to but we have disconnected all circuits, proved they not showing any earth faults (all above 500Mohms) and all have expected resistance when E-Stops are closed (in normal position) and all go open circuit when opened (around 1.5Kohms on a couple of the longer runs). They are all wired directly back to ESD panel and then series up inside the panel. When we activate any of the E-Stops intermittently 40% of the time the relays fail to open and sometimes try but chatter. This is not acceptable as we all know. Without completely redesigning the system i thought a quick fix to get the system back working until we go to engineering to redesign with safety relays etc etc would be to instal the isolation TFMR on the supply and by tying the L2 side to Earth would give us the 0V on L2 and 230V which will be 0V when E-Stops are activated. This would absolutely guarantee the system will work as it should and give us time to re-design the system to a SIL level 2 or 3 as it should have been in the first place.

It is a bit awkward as i am trying to get this fixed so not to compromise safety of our systems but as its a safety system we need engineering approval and thats the sticking point as they will not admit the design flaw. I have contacted Schneider who have agreed the relays may not operate efficiently with this type of supply so i think this is a good temporary option. The relays for information are just normal Schneider general purpose relays, they are not even safety relays which in my opinion is very sloppy design.

For information i have tested this before suggesting the fix and it worked as i though but i needed to remove it as it was not approved. My only concern was maybe the L2 to earth but as its isolated and no exposed metal parts at all in the circuit i risk assessed and deemed it acceptable to allow the system to work correctly again.

We could install bleeder resistors i suppose but again that would be a modification of the system and need approval so i was hoping to completely eliminate it with theTFMR.

I think we all agree it is a very strange one and one i have not come across before. It has been a good fault finding journey and a good learning curve also.

Ok guys, thank you all for the input.

Without leaving myself open and revealing too much private info its a 3phase no neutral 230V supply to DB then single phase 230v feeding the DB for the ESD system. 130V to Earth each phase (no neutral). 6 E-Stops for full engine shut down system all series up so any one opens it opens the circuit and should in theory allow the relay to drop out and stop the engines, fail safe in theory. I would of liked to have seen a double E-Stop circuit so its a positive open when activated as both legs drop out and you dont get false shutdowns should one leg fail but it is not and only one leg so even a loose connection should in theory shut the engines down, again not a good design.

A couple of the cable runs are very long as AJ eluded to but we have disconnected all circuits, proved they not showing any earth faults (all above 500Mohms) and all have expected resistance when E-Stops are closed (in normal position) and all go open circuit when opened (around 1.5Kohms on a couple of the longer runs). They are all wired directly back to ESD panel and then series up inside the panel. When we activate any of the E-Stops intermittently 40% of the time the relays fail to open and sometimes try but chatter. This is not acceptable as we all know. Without completely redesigning the system i thought a quick fix to get the system back working until we go to engineering to redesign with safety relays etc etc would be to instal the isolation TFMR on the supply and by tying the L2 side to Earth would give us the 0V on L2 and 230V which will be 0V when E-Stops are activated. This would absolutely guarantee the system will work as it should and give us time to re-design the system to a SIL level 2 or 3 as it should have been in the first place.

It is a bit awkward as i am trying to get this fixed so not to compromise safety of our systems but as its a safety system we need engineering approval and thats the sticking point as they will not admit the design flaw. I have contacted Schneider who have agreed the relays may not operate efficiently with this type of supply so i think this is a good temporary option. The relays for information are just normal Schneider general purpose relays, they are not even safety relays which in my opinion is very sloppy design.

For information i have tested this before suggesting the fix and it worked as i though but i needed to remove it as it was not approved. My only concern was maybe the L2 to earth but as its isolated and no exposed metal parts at all in the circuit i risk assessed and deemed it acceptable to allow the system to work correctly again.

We could install bleeder resistors i suppose but again that would be a modification of the system and need approval so i was hoping to completely eliminate it with theTFMR.

I think we all agree it is a very strange one and one i have not come across before. It has been a good fault finding journey and a good learning curve also.