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Three Phase 230V three wire systems

We have a emergency shutdown system on our rig that is wired in such a way the relays always have a minimum of 90v on L2 side of the coil so it is intermittently not opening on ESD activation. I believe this is incorrectly designed as we have a three wire three phase system, no neutral so in theory 110v each phase and 230v across any two phases.

Intermittently when activating the ESD buttons the activation relays will not open because of the constant voltage of anywhere between 90-110v on L2. I am trying to convince my engineering department that this is incorrect and we need to redesign but it is difficult as they don't understand the issue.

What i would like to propose to temporarily fix the issue is to put in a Isolation transformer and tie down the L2 side to earth of the secondary to give us a 0vL2 and 230v L1. This guarantees the relays will work when intended but i am not 100% sure this is allowed?

Can someone please assist me if at all possible.

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  • I think I  agree with broadgage it sounds like an odd system but is there any chance of a sketch of a simplified circuit  or at least the key bits of it ? 

    Clearly any emergency stop design that does not always stop is unfit for purpose (well yes !), but I'd like to understand better what is going on.
    One end of a coil being live does not mean it is 'on'  if the other end is open circuit, just that it is floating live,  but of course any path to ground even if unintended means that some current will flow. Yes transformers are allowed but you may have to think about how things fail to safe - for this reason most EM switches are N.C as a power cut , or a broken cable also look like the kill signal.

    Anyway, an interesting one.

    regards Mike

    (consultant engineer, but I'd need the buy in of my employer to comment professionally)

Reply
  • I think I  agree with broadgage it sounds like an odd system but is there any chance of a sketch of a simplified circuit  or at least the key bits of it ? 

    Clearly any emergency stop design that does not always stop is unfit for purpose (well yes !), but I'd like to understand better what is going on.
    One end of a coil being live does not mean it is 'on'  if the other end is open circuit, just that it is floating live,  but of course any path to ground even if unintended means that some current will flow. Yes transformers are allowed but you may have to think about how things fail to safe - for this reason most EM switches are N.C as a power cut , or a broken cable also look like the kill signal.

    Anyway, an interesting one.

    regards Mike

    (consultant engineer, but I'd need the buy in of my employer to comment professionally)

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